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'High-Yield Neuroanatomy 1 I . . .........................................................................................................................................................................................................
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Jarnes D. Fix, Ph.D. Profe~sor Emeritus of Anatomy
Marshail University School of Medicine
Huntington, \V'est Virginia
~~ LIpPINCOTT WILLIAMS & ~ILKINS .. A Wolters Kluwer Company
Philadelphia • Baltimore • New York • london Buenos Aires • Hong Kong • Srdney • Tokyo
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2nd~ition
__ Copyright Cl2~",() by L.irrincott Willinms ~ Wilki!ls.
Copyright C> 1995 by Wjlliams &. Wilkins.
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Materials appearing in this book prepared br individuals as r<lrt ortheir official duties as U.S. GO\'emment employees are not cO\'ered by the at-o\'e-mentioned copyright.
Fix. ]3.lnes D. High-yield ''''" r0anatom}' I James D. Fix.-2nd ed.
p. ; cm. - (High-yield series) -.'.--"~:~:.
Includes index. ISBN 0-633-30721-5 L !'Jeuroanatomy--Outlines, syllabi. etc. 2. Neuroanatomy-Examinations. questions.
etc. I. Tide. II. Series. [D~lLM: 1. Nervous System-anatomy & histology-Examination Questions. 2. Nervous System-anatomy & histology--Oudines. 3. Nen'ous System
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The authors, editors, and publisher ha\'e exerted e\'er/' effort ro ensure that drug selecrion and dosage set forth in this text-are in accordance with current recommendations and practice at the time of pubiication. Howe\·er. in \'iew of ongoing research. changes in gO\'emmem regulations. and the constant flow of information relating to drug the rap}' and drug reactions. the reader is urged to check the package insert for each drug for an}' change in indications and dosage and for added warnings and rrecautions. This is l'<1rticularly imrortant when the recommended agen: is a new or infrequently employed drug.
~."--:.-
Some drugsandmcidical devices presented in this publication have Food and Drug Ad-~~ ministration (FDA) clearance for limited use in restrictcJ research setrings. It is the responsi- -bility of the health care provider to ascertain the FDA Wltus of each drug or device plar{ned for use in their clinical practice.
The second editiol~ of Hi?0-Yield Nellroa'n{1comy is still ne.uroanatamy at its irreducible minimum, con~ raining most, if not all, of the 'national board themes, The sole purpose of the book is to get you through the nen'ous system topics cO\'ered on the United Scates Medical Licensing Examination (USMLE) Step 1. Substantial <1ddi~ions ha\'e been made to accommodate' student requests and suggestions.
NEW TO THIS EDITION • Mini~atlas of nuclear magnetic imaging scans • Carotid and \'enecral digital subtraction angiography • Nuclear magnetic angiography • Additional figures of cranial nerye function componems • Chapter on aphasia. apraxia. and dysprosody • Index
TO THE STUDENT To make the most of this book, stud), the illustrations, computed tomography scans, and magnetic resonanc~ images carefully, and read the legends. Many board-type questions come from this source. In fact, the answers to at least 20 common USMLE questions are found within this preface. Finally, remember these tips as you scan the chapters:
Chapter 1: The mini-atlas pro\'ides you with the essemial examination structures labeled on computed tomography scans and magnetic resonance images.
Chapter 2: Cerebrospinal fluid pathways are well demonstrated in Figure 2-1. Cer~brospinal fluid is produC'ed by the choroid plexus and absorbed by the arachnoid villi t.hat jut into the venous sinuses.
Chapter 3: The essential arteries and the functional areas that they irrigate are shown. Study the carotid and vertebral angiograms and the epidural and subdural hematomas in computed comography scans and magnetic resonance images. ,/
Chapter 4: The neural crest and its derivatives, the dual origin of the pituitary gland, and the difference between spina bifida and the Amold-Chiari malformation are presented. Study the figures that ill.ustrate the Arnold-Chiari and Dandy-Walker malformations.
Chapter 5: What is the difference between Lewy and Hirano bodies'? Nen'e cells contain Nissl sub-, stance in their perikarya and dendrites, but not in their axons. Remember that Nissl substance (rough endoplasmic reticulum) plays a role in protein synthesis. Study Figure 5~2 on the localization and prevalence of common brain and spinal cord tumors. Remember that, in adults, glioblascoma multiforme is the most common brain tumor, followed by astrocytoma and meningioma. In children, astrocytoma is the most common brain tumor, followed by medulloblascoma and ependymoma. In the spinal cord, ependymoma is the most common tU\;10r.
Chaptt!r 6: The adult spinal cord tcrminiHcs (conus terminalis) m the lower border of the first lumbar \'crtebra. The newborn's spinal cord extends to thc third lumbar vcrtebra. In aduIes, the cauda equina extends from \'crtcbr<ll IC\'cls L-2 to Co. .
Clw/w)' 7: The tracts of the spinal cord arc rcduced to four: corticospinn\ (pyramidal), dorsal coh:~~~~. !,;lin ;md tcmpcr;uurc, and Horner's. Know thcm cold.
Ix
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x Preface .................................................................................................................................................................................................................. -
ChatHa 8: Study (he eight c1:1s:;i~ nmillllall'oard Idkms of (Ilt! spinal cord, Four hc,wy hiners an~: Rrl.lwn-Sequard syndrome. BI:! ;wit,\Inino:;is <,sllbnclItt! combint!~ dcgcncmtion). syringomyelia, and al1lyotwphic btewl sClerosis (LI.)lI Gehrig':; di::c:1sc).
Chapc!!!' 9: Study the trans\'crse st!ctions l)f (he brnin stt!tn, and k)cali:e the cranial nerve nuclei. Scudy . the \'~ntral surface llf (he ~min stem, nnd id~ntify the exiting and eprering crani:11 nen'·cs. On thc
dorsal s\,rfac'c \')f the brain stem, identify the only exiting cranial nerve, the trochlear ner\'e.
Chaprer JO: Cr.mial ner\'e.(CN) V-I is the nfferent limb oftht! corneal reflex, CN V-I, CN V-2', eN III, CN IV, CN VI, and the postganglionic sympathetic fibers are all found in the cavernous sinus.
Chapter 11: Figure 11-1 shows the auditory pathway. \Vhm .1re the cau:;es of conduction and sen$l)rineuml deafness? Describe the \Veber and Rinne tuning fl.)rk t~srs, Remember that the auditory ne,r\'e and the organ of corti nnd derived fron~ the otic placode.
'Chaprer 12: This chapter descri~es the r~\"O typ~s of \'e$[ibubr n'ystClgmus: rostrotational and caloric' (CO\VS acronYl'n). Vestibl.Jlo-ocular reflexes in the 'unconscious pntiem are also discussed (see Figure 12-3),
Chapter 13: This chapter on the cranial nen'es "is pi\'oral. It spawns m.ore neuroanatomy examination questions than any other chapter. Carefully study all of the figures and legends. The seventh cranial nerve desen'es special consideration (see Figures 13·3 and 13--f). Understand the difference between an upper motor neuron and a lower .motor n~uron (Bell's palsy).
Chapter 14: The three ~nost important lesions of the brain stem are occlusion of the anterior spinal arceI')' (Figure 14-1), occlusion of the posrerior inferior cerebellar artery (Figure 14-1), and medial longitudinal fasciculus syndrome (Figure 14-2). \Veber's syndrome is the most common rnidbrain lesion (Figure 14,3).
Chapter 15: Figure 15-1 shows the most important cerebellar circuit. The inhibitory -y-aminoburyric acid (GABA)-ergic Purkinje cells gh'e rise [0 the cerebellodentatochalamic cract. What are mossy and climbing fibers? . •
Chapter 16: Figure 16·1 shows e\'eI')'thing you need to know about what goes in and what comes out of the thalamus. Know the anatomy of the internal capsule; it will be on the examination. \"X1hat is the blood supply of the internal capsule {stroke}? "-
Chapca 17: Know the lesions of the \"isual system. How'are quadrantanopias created? There are t\\'o major lesions of the optic chiasma, Know them! \Vhat i$ Meyer's loop? .
Chapcer 18: The imporra;1t anatomy of the auror,lOmic nervous system is clearly seen in Figures 18-1 and IS·2. .
Chaprer 19: Figures 19·1 i1nd 19-2 show that the para\'entricularand supraoptic nuclei synthesi:e and release antidiuretic hormone and oxytocin. The supraehiasmatie nucleus receives direct input from the redna and plays a role in the regulation of circadian rhythms.
Chapter 20: Bilateral lesions of the amygdala result in Kluver-Buey syndrome. Recall the triad hyperphagia, hypersexuality, nnd psychic blindness. Memory loss is associated with bilateral lesions of the hippocampus. \Vernicke's encephalopathy results (rom a deficiency of thiamine (vitamin B). Lesions are found in the mamillMy bodies, th:-\1C1InlIS, and midbrnin tegmentum (Figure 20-3). Know the Pa· pez circuit, a common board question.
Chapur 21: Figure 21 -) shows the circuitry of the basal ganglia ;1I1d their associatcd neurotransmit· ters, Parkinson's disease is C'lssociated with a depopubrion of neurons in the substantia nigra. Hunt· ingcon's disease results in a 105s of ncn'c cells in the caud:1[e nuclell'> nncl put;ll11en. Hcmiballism rc' suits frl)Jn infarction of the contTC'I\;ltl'T.)1 suhthnlC"lInic nucleus.
Clw{Jtc'r 22: In this chnprer, the l';uh\\'OIYs of the m;)jor neuflltr;lll\illittC'lS ;1[(: :;]10\\'11 in sC'r>;I::lrt~ br:)in ! 11 : 1 p S C; l '-I ~ :': 111 ; 1 t cis the 1\):' j 0 r c :\ cit ;l ((\ r)' tr; m S III itt t: r (l the l)f : Ii: : . ( ;. '\ ; \. \, : : ; i""' ;:'. i (': :;' h ; : .' (j.' 1 .• , ; 1 '
·~it~~r. PurHnje celh-; of the ·cl;.·rrbelium are GABA*ergic. In Alzheimer's disease, there .is a loss of nc~tylchl'lin~rcic neurons in dl~ basal nucleus of Meynerr. In Pnrkinson's disease, there is a loss of dllpmninergic nelJrons in the sllb~tnntia nigra.··· ..
Ch(lpr~r 23: This chapter' describ~$ rhe cl.."Irricnllocalbuion of functional ar~as of rl~e br;in. How d\."Ies rhe d')l1\inant hem.isphere differ fn."Im the nondominant hemisphere? Figure 23-4 shows the effects of
"'arh"us major henlispheric lesions', \Xlh;u: symptoms result from a lesion of the right inferior parietal . lobe! \'Vllat is Gerstmann's syndrome? ,,-... .. . .
Chaprer 24: This chapter describes apraxia. aphasia, and dysprosodr, .Be,able to,differentiate J?roca's aph~l$ia fromWemicke's aphasia, '\Vhar is conduction aphasia? This is board-relevant.material. I "'ish rou good luck,
I wish [Q th;mk my ll1:edical studen.ts. ~olleaglles, and members of the staff of Lippin~ott \Villiams & . \Vilkins for their ,-alual:-le comments. suggestions. and help. Thanks also go [Q Elizabeth Niegin·ski for her editorial direction.
.1. .. Cross.~Sectional Anatomy of the Br~in .. ' ..•..••.•.•..•..•...• ~ I. In~roJu.:tion 1
2
3
II. ~ Hd$~\gict:al scctkln
III. Coronal section thrl'ugh che o~~i:ic chiasm 3 IV. Coron"l section thf\,'\ugh the mamillary bodies 4 V. A.xial image through che chalamus and internal cClpsule 5
VI. A.xial iinage through ~he Il~!~braln, 1l1<1rnillary bodies, and optic mict 6 . ;--:-.. - ~
Meninges, \Tentricles, and Cerebrospinal Fluid ........ : I. ~ fenihges 8
II. Ventricular system 10 '". Cerec.r\."Ispinal tluid It IV. Herniation 11
. . . . . . .
Blood Supply .............. .- ........................ . (. The srinal cord and lower brain stem 1 = <J
II. The internal carotid system 16 III. The \'en:ebrobasilar system 17 IV. The blood supply of the internal <;:apsule 18 V. Veins of the brain 18 VI. Venous dural sinuses 18
VII. Angiography 18 VIII. The middle meningeal artery 19
4 Development of the Nervous System I. The neural tube 24
III. The anterior neuropore 26 IV. The pOsterior neuropore 26 V. Microglia 26
VI. Myelination 27 VII •. Positional changes of the spinal cord 27
VIII. The optic nerve and chiasma 27 IX. The hypophysis 27 X. Congenital malformations of the CNS 27
Neurohistology ......... . I. Neurons 30
II. N i~sl substance 31 III. Axonal transport 31 IV. Wallerian degeneration 3 r . V. ChromacolYSis 31
VI. Regeneration of nerve cells. 31 VII. Glial cells 31
VIII. The blood·hr<lin harrier 32 IX. The hlood·CSF harrier 32
. . . . . . . . . . . . . . . . . . . . .
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. . . . . . . . . .
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..........
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vi Contents I ........................................................................................................................................................................................................
X. Pigment:: ;tnJ' !I\dll:'k'n~ .32 I XI. The! cla:':'itl~~ltil\n '-It' n~rYI.' iil'l.'r:: 32 XII. Tum('r$ ,'i"th~ C~S :\I\~J rNS .'3'
III. Ll'c~ciol\ ,'f chI.' m.aj~~r m~'cllr ~md seml'ry l1uciei of che spinal c,-,rd IV. The C<lUJ;l c:quina ) I
V. 111e my,'c.ltic retlex 3 j
7 Tracts of the Spinal Cord' .......... . I. Incrodu .... ·ckm 35
. . . . . . . . . II. Dl'r$(ll c ...... lumn-mediallemnisclls pachway 38
III. Lateral :orinoch:llamic tract 40 IV. Laceral c .. 'n:ic('$rinal cracc 40 V. Hn., .... "\th~lb.m05rinal tract .. H
37
8 Lesions of the Spinal Cord ............ . I. Disease:, .. ,t the motor neurons and corticospinal craccs 4j
. . . . . . . . . II. Sensory pthway lesions 47'
'". Combinc:d mOWr and sensory lesions 47 IV. Peripher.'!.l ner\"ous system (PNS) lesions 48 V. lnt:ervene'tra.l disk herniation 4S
. . . . . . .
9 Brain Stem ............... ' .......•..................... I. O\'erview 49
11. Cros5-section through the medulla 49 III. Cross-section through the pons 51 IV. Cross-section through th:: romal midbraill 52 V. Corticol:-ulbr fibers 52
1.0 Trigeminal System I. O\'ervicw 53
II. 11le trigeminal ganglion 53 III. Trigeminothalamic pathways 53 IV. Trigeminal ret1exes 55 V. The cavernous sinus 57
II. The visual pathway 91 III. The pupillary light ret1ex pa,thway 93 IV. The pupillary dilation pathway 93 V. 'The near reflex and accommodation pathway 94
VI. Cortical and subcortical centers for ocular motility 94 VII. Clinical correlation 96
:18 Autonomic Nervous System ............................... 98 I. Introduction 98
II. Cranial nervcs with parasympathetic components 98 III. Communicatin.£,: rami 98 IV. Neurotransmitters 98 V. Clinical correlatioll 101
:19 Hypothalamus .......•................................. 103 I. lntrouuction 103
II. The ~ix-layered n~'-"'C0rt~x 121 /II. FuncriL'nal area:' 1: i . IV. Focal descrucri\"ce hcmi~rheric le~ions and srmrcoms 127 V. Cere hal dominance 1::: 7
VI. Split-l:-rainsyndron1C 128 VII. Other le~ions of the cOTj:'US callosum 128
VIII. Brain and spinal cor.i rumors 128
24 Apraxia, Aphasia, and Dysprosody .......•.................. 129 I. Apra:da 129
I. INTRODUCTION. The illustrations in this chapter are accompanied by corresponding magnetic resonance imaging (MRl)" scans. Together tl}ey' repr~sem a mini~atlas of brain slices in the three orthogonal planes (i:e., midsagittal, coronal, and axial). An insert on each'figure shows the le\'el of the slice. The most commonly tested structures are labeled.
II. MIDSAGITTAL SECTION (Figures i-:1., :1.-2,·and :1.-3). The location of the :muctures shown in the figures should be known'.
Interventricular foramen
Septum pellucidum
Anterior commissure
Lamina tenninalis ,;:---.::::....----...-J
Corpus callosum
Thalamus Motor strip
ntraJ sulcus Sensory strip
Third ventricle --.:b-----"'\/f::1.
Superior and inferior colliculi (tect~m) .
Calcarine sulcus
Fourth ventricle
Cerebellum (vennis)
Medulla oblongata
Figure :1-:1.. ~ti,k\gittal scction (I( the hwin anJ hrain stem shOWing the structures sllrrounding the third allJ (nurth vcntricles. The hr;lin :.tell) incluJes the miJbrain (M), pons 0), and meJulb oblongata.
Figure .1.-2. ~\1idsagittal magnetic resonance imaging secrion through the brain and brain stem showins: IT iml:'orram structures surroundinll the third and fourth ventricles. This is a Tl-weif!hced ima£e. The IZra\' m:'nt is gray (hypoimense), whereas the white matter is white (hyperimense). - - _.
• " Cross-Sectional Anatomy of the Brain ........... ~ ........ '" ........... ~ ........................................•....... ;. ......... -.. , ............................................. ; .................... : ....... -.................. . I~J. CORONAL SECT,ON THROUGH THE OPTIC CHIASM (Figures :1.-4 and 1.
The k"lcution of [he s~ruc~ures sl~o\\"n in the figures should be known.
Caudate nucleJs
In:emal Corpus callosum
Lateral ventricle
Septum pellucidum
Pu:ame.,
Insula
Figure :1.-4. Coronal secck'n of the brain at the b'el of the anterior commissure, optic chiasm, and amn dala. Note that the internal carsule lies between the caudate nucleus and the lentifonn nucleus (globus pallidl an.:3 putamen).
Figure :1.·5. CCJronal Inilgn('tic rcsonancc im;lt:inj.! :<cction throllgh thc mnygJa!a, (.1ptic chiasma, infundihulum, find intcrn;]l capsulc. Till' Ci\\"crnous !iil)ll~ ("ncirdcs the sella !orcien and contains thc following structures: cranial nerves (eN) fll, IV. V/. V-I, ;lnJ V-2; posIl,;anJ.,:lionic syml':lIhcric fibers; nnd thc internal cnrotiJ anery. This is a TI-wcightcd image.
.1 ; . ". " . mc' », '.r.
I 4 Chapter 1 1
" .... , ............................................. .., ............... ~ .............................................................................................. , .................................. . IV. CORONAL SECTION T~ROU.GH THE MAMflLARY BODIES (Figures" 1.6 am
1· 7). The Illcntion of the str~lc(Url:S shown in the h¥ures should be ~no\\'n.
lateral ventricle
Internal capsule
Third ventricle
Subthalamic nucleus
Substantia nigra
Mamillary bodies
Fornix
Caudate nucleus
~-I;:;:;"'-~~'ffo.;~'-- Thalamus
IT~~.:.u._ Insula
Putamen
Optic tract
Hippocampus
Figure 1-6. Coronal section of the brain at the b'el of the thalamus. mamillary bodies. and hippocampal formation. Note thac the internal capwle lies between the thalamus and the lentiform nucleus.
v. AXIAL ,IMAGE THROUGH THE THALAMUS AND INTERNAL CAPSULE (Flgures :1.-8 and 1-9). The Jocation of the srruccures shown 'in the figures should be known: " . .
Corpus callosum ,
Septum pellucidum -t.~fI:1Oii::IL
Fornix
Third ventricle
Corpus callosum (splenium)
Superior colliculus
,lateral ventricle
I Q!UCl'atanucleus
Intemal capsule ,..~~~( . (anterior limb)
Pineal gland
Internal capsule (poslerior limb)
Thalamus
Caud~le nucleus (Iail)
Figure :1-8. Axial section of the brain at the b·d of the internal capsule and basal ganglia. Note that the internal capsule has an anterior limb, a genu, and a posterior limb~ Note also that the corpus callosum is sectioned through the genu and splenium.
•
Lateral ventricle
Septum pelludicum and fornix
-·-"~'-T--
Putamen -.........,::'::i'-~
Globus pallidus _--+=:~
Insula --+.;;'"
External capsule -.-.,..,
Velum inlerpositum
Superior sagittal sinus ___ ~. ':":'-:-__ ---.
--."',.~-~"'-.-
.........
Corpus callosum (genu)
Caudate nucleus
Internal capsule (anterior limb)
""""--Internal capsule (genu)
~"""""-Internal capsule (posterior limb)
---..,--'--.. Thalamus and third ventricle
Trigone
Corpus callosum (splenium)
Visual radiations
;....--:-:!~~':-Vjsual cortex
Figure :1~9. Axial mag-netic resonance imaging scctiollllt the b'd of the internal capsule nnd bas;' ganglia. Note thac the caud,lte nucleus hulges imo the frontal horn of the lateral ventricle. In Hunringwn's disease, there i~ :-: :-:::::':;;"c loss of -y-arninohutytic acid (GABA)'crgic ncurons in the caudate nuclclIs that results in h).clro. ccrhalus cx vacuo. A ICliion Clf the S;Clllllli the internal cap:;ulc resu!rs in a contralaccrnl wcnk lower face with sparing of the upper face. This h a TI-wdghll'd image.
VI. AXIAL IMAGE THROUGH THE MIDBRAIN, MAMlLLARY BODIES; AND OPTIC TflACT (Figures 1-1Q, 1-11, 1-12, ~nd 1-13):Thc!ocncion of the :;truCtur~~ shtl\\"l'\ in the tigur~s :;hl..)uIJ be known.
~~~~~- Substantia nigra
r""'_,~ Red nucleus
lateral ventricle
Cerebellum
Hippocampus
Trochlear nucleus
Nucleus 01 inferior cOlliculus
Figure :1.-:1.0. .-\xial section of the l.-rain at the le\'e! of the midbrain. mamillary bodies, and amygdala. ~o(e that the substantia nigra separates the crus cerebri from the tegmentum of the midbrain.
Figure. 1.-1.2. Axial magnetic resonance imaging section at me level of the optic chiasm, mamillary bodies, and midbrain. This patient has neurofibromatis type 1 and an optic nerve glioma. Note the size of the right: cptic nerve. 11le infundibulum is poscflxed. This is a Tl-weighted image.
FIgure 1.-1.3. Axial magncric rc!;onancc imaging H'ctioll at the le\'eI of the uncal incisure, oculomotor nerve, anJ inferior colliculus. Is thcre pathology within ,he ()rhit?
I. ~ENINGES are three ~onnecti\'e tis~ue mem.brnnes 'that surround. the spinal cord Clnd brain.
A. They consist L'If the pia mater, arachnoid, and dura mater.
1.. The pia mater is a delicate, highly vascular layer of connective tissue. It closely covers the surface of the !:-rain and spinal. cord.
2. The arachnoid is a delicate, nonvascular connecth'e tissue membrane, It is located between the dura mater and the pia mater.
3. The dura mater is the outer layer of meninges. It consists of dense connective tissue.
B. Meningial spaces
1.. The subarachnoid space (Figure 2-1) lies between the pia mater and the arachnoid. It terminates at the level of the second 'sacral \·ercebra. It: contains the cerebrospinal t1uid (CSF).
2. Subdural space a. In the cranium, the subdural space is traversed by "bridging". veins. b. In the spinal cord, it is a clinically insignificant potential space.
3. Epidural space a. The cranial epidural sp;lce is a potential space. It contains the meningeal ar-
teries and veins. ... b. The spinal epid':lral space contains fatty areolar (issue, lymphatics, and \'enous
plexuses. The epidural space may be injected with a local anesthetic to produce a paravertebral ("saddl~") nerve block.
C. Meningial tumors
:1. Meningiomas are benign, well-circumscribed, slow-growing tumors. They accoum (or 15% o( primary intracranial tumors and are more common in women (han in men (3:2). ,Ninety rer(e~1[ of meningiom~s are supratentorial.
2. Subdural and epidural hematomas a. Subdural hematoma is calls<;d by bceration of [he superior cerebral (bridging)
veins. b. Epidural hematoma. is CCluscJ by Inccration of the middle meningeal artery.
D. Trauma
E. Meningitis is infbmm;Hion o( the pi;Hlr;lChnoiJ :1;"(';1 of the bLlil1. til:' spin;-t1 cord, or
Figure 2-1.. The subarachnoid spaces and cisterns of the brain and spinal cord. Cerebrospinal tluid is prodilCed in the choroid plexuses of the ventricles. It exits the fourth ventricle. cir-culates in the suba~achnoid space, and enrers the ~uperior sagittal sinus through the arachnoid granulations. Note that the conus medullaris terminates at L-l_ The lumbar cistern ends at S-2. (Reprinted with pemlission from Noback CR, Scrominger NL. Demarest R: The Human NenxJl(s System. 4rh ed. Baltimore, Williams & Wilkins. 1991, p. 68.)
:1. Bacterial meningitrs is characte~ized clinically by fever, headache, nuchal rigidity, and Kcrnig's sign. (With the patient supine, the examiner flexes the pntienc's hip, but cannot extend the knee without causing pain. It is a sign of meningeal irriwcion.) [Rcmemher: ~ernig == knee.] More th;m 70% of cases occur in children younger thlln 5 years of age. The disease may cause cranial nerve palsies Ilnd hydrocephalus.
'!: ~-;,'i:·~'. -;~.;: ... " ...... '.,. . '')-
=,~' ... ~~ ... : :," ~., ·t I
10 Chapter 2 .' ...................................... ~~ .... ~:.:.~~:~ .. ~;~.~~:~ ............................... _...................................................................... ................. I (1) In 'newborns, bacterial meningiris is most frequendy ea'used by Group E
str~rtoc\.lCCHSll'l.">lOCoctItS agalactiae) ClnJ Escherichia coli." I (2) In older infants and young children, it is most frequenrly causeJ b~
H(l~mophilllS injlltt!llzat!. . (3) In young adults, it is most frequently caused .by Neisst!r;a mell;ngitidis. I (4) In older adults, it is most frequently 'Clused by Streptoc.occliS pnewlloniae.
b. CSF findings . (1) Numerous polymorphonuclear leukocytes (2) Decreased glucose le\'els (3) Increased protein le\'e!s
, 2. Viral meningitis is also known as aseptic meningiris. Ie is characreri:ed clinically
by fe\'er, headache, nuchal rigidity, and Kemig's'Sign. .. a. Common causes. ~lal'\y \'iruses are ~ssociated with viral m~ningitis,-includ
ing mumps, echo\'irus, Coxsackie virus, Epstein-Bart virus, and herpes simplex tyre 2.
A. 111e choroid plexus is a specialized structure that projects into the lateral, third, and fourth yenrricles of the brain. It consists of infoldings of blood \'essels of the pia mater that are cO\'ered by modified ciliated ependymal cells. It secretes the CSF. Tight junctions of the choroid plexus cells form the blood-CSF barrier.
B. Ventricles contain CSF and choroid plexus. . .'
:to The twO lateral \'entricles communicate with the third ventricle through the intefyenrricular foramina of Monro.
2.' The third ventricle is located between the medial walls of the"cliencephalon. It communicates with the fourth \'enrriele through the cerebral aqueduct.
3. The cerebral aqueduct connects the third and fourth ven'trides. It has no choroid plexus. Blockage of the cerebral aqueduct results in hydrocephalus.
4. The fourth ventricle communicates with the subarachnoid space through three ourlet foramina.
C. Hydrocephalus is d,ilation of the cerebral ventricles caused by blockage of the CSF }'i1thways. It is characterized by excessh'c accumulatiol) of CSF in the cerebral ventricles or subarachnoid srace.
1. Noncommunicating hydrocephalus results from obstruction within the ventricles {e.g., congeni[;)1 (lqued~Jct:l1 stenosis).
2. Communicating hydroceph~lus resulrs from blocbgc within (he subarCichnoid sp:lce (e.g., adhcsions after mcningitis). .
3. Normal~pressurc hydrocephalus occurs when thc CSF is not absorbed by thc arachnoiJ villi. It may occur sccondmyto posttf:lullwtic Illcning/?;1! hemorrhage. Clinically. it is ch:nDctcrizeJ by thc (riC'ld of progrcssivc dCll1cnri:1, ataxic gait, :1I1d IIrin;lry incontinence. (Rememher: wacky, wobbly, :md wct.)
,oresistal\c~ 'to CSF outflow at the ;lmchnoid '·iIli.-Ie occurs in obese young women and is ch .. \mcteri:eJ by p.lpillcdemn withollt mass. elevated CSF pressure, and de'
o rerio'rnting \·i~k)n. Th~ ,·encricles may be slit,!ike.
1If. CEREBROSPINAL FLUID is oil colorless acellular fluid. It tlows through the ventricles nndinto the sulxu-.lChnc..)id space.
A. Function
i. CSF- supporfs the central nervous system (CNS) and 'protects it against' con' . cussi,·e injury.
2. It transports hormones and hormone,releas(ng facrors.
3. It remo\-es ~netabolic waste produEts 'through absorption.
B. Formation and absorption. CSF is formed by the choroid plexus. Absorption is pri, marily through the arachnoid villi into the superior sagittal sinus_
C. Th~ c~mposition of CSF i,s clionica11)ftelevant (Ta):>le 2-: 1 ).
1. :rhe nomlal number of mononuclear cells is less than 5h-d.
2. Red blood cells in the CSF indicate subar?chnoid hemorrhage (e.g., caused by trauma L"r a ruptured 1:-err)' aneurysm).
3. CSF glucose h~\·els are normaHy 50 to 075 mg/dl (66% of the blood glucose level). Glucose le\-els are nonnal in patients with viral meningitis and decreased in pa,o tients with bacterial meningitis.
4. Total protein levels are normally between 15 and~45 mg/dl in the lumbar cistern. Protein le\'els are increased in patients with bacterial meningitis and normal or slightly ~ncreased in patients with yiral meningitis.
5. Normal CSF pressure in the lateral recumbe~t position ranges from 80 to 180 mm H 20. Brain tumors and meningitis elevate CSF pressure.
Table 2·i Cerebrospinal Fluid Profiles in Subarachnoid Hemorrhage, Bact~rial Meningitis, and Viral Encephalitis
Figure 2-2. Coronal section of a cumor in the surrarencorial COl11partmenc. (1) Anterior ceret-ral artery; (2 wbfalcial hemiation; (3) shifting of "etmicleSi (4) pO~teri2r ~erehal arter)' (c~ll1Fression results irr..C.ontralacer .. , hemiclUopia): (5) uncal (cranscencorial) herniation; (6fRernohan's notch, with damaged corticospinal and Cor ticobulbar fibers; (7) tentorium cerebelli; (8) prramiditl cells that give rise to rhe COrticospinal traCt; (9) tonsil. lar (transforaminal) herniation, which damages viral medullary cencers. (Adapred with pennission from LeedR\V. Shumann RM: J\'eilropatholog)" New York, Harper & Ro\\". 1982, p.16.)
Figure 2-3. Axial section through th~ midbrain nn.lthc hcmi(l(ing parahippocnmpal grrus. TI1C left oculomotor nCITC is b<:ing !ltr<:tchcd (dilated 1'1I1'il). The left 1")~lcrior cerebral nTtery is COlllprcs~cd, resulting in a contrClhltcral hemianopia. The right crus cerebri is dam;lbC'\ (Kcrnoh"l)'s notch) b)' thc (rec edge of the tentorial inchurc, rcsulting in a contr<llarcral hell\il';lTc:ii~. KCnll'han's 1)0tch re:\\Ilts in il ("Isc localizing sign. TIle caudal "';;·'I,:·/u.:rnent ot" the hrain !>tern C;lll~es rllJ'lItrc of the I\Ir,l1n('.1i;1I) "Ttcrics of the h;lsibr ;lTlcry. H
crnorrh:1{.:c into
the rniJhrain and f(J~tral pontine Icgm~'l\lull\ i~ usuall)" (Ha! (Durct hCl1)orrh:l/;cS). The I'll~tCI ior (ercbr;,! arterics f ic .~\lpe rior 10 the: oculomotor nCf\TS. (I) r;\f:lhi)'l'PC;11l1i\1! ):ynl': (2) en:, l'c'l ',+:i; (J) I'll;,! (' I;' 'I C Ilrc! ,r;" i1f, c ry. (';\'HHic
n<:rv(:;(5)oPticc'I:\,m:l;"qdl1Ilh\(llr:'.(\\\,(I)i:' ',i .:'" (·\ii',::·,.,! !. , [· .. l
. Figure 2-6. Computed tomography axial section showing an epidural hematoma and a skull fracture. (A) Epidural hematoma; (B) skull fracture; (C) calcified pineal gland; (D~ calcined glomus in the trigone region of
. the I "ern I ,·emric/e. The epidural hemaroma is a ~,~~:i~ :~~\.e~:,~:,~:n~(o:,:;~~:~~V"C" (i
II. THE INTERNAl,. CAROTID SYSTEM (see Figure 3,1) consists of the internal carot a rtery and its branches ..
.', ".:"
.. : .,.~' ... ~:-~.','
A. The ophthalmic artery emers rhe. orbit with the optic nerve (eN II). The centl artery of the r~tjna is'a 1::-[",1I1ch of the orhthnlmic mtery. Occlusion results in blindne:
B. The pos~erior com.municating ~rtery irrigmt's. th~.I:'Ypoth~s and \"~~~rClJ th:ll mus. An aneurysm of this mrery is t11e second most common aneurysm of the drc of\Villis. It commonly results in third,nerve palsy.
~ante_d9X choroidal ar.tery_arises from the internal carotid ~rrery. Ie is not pan: \ the circle of \Villis. lr rerfuses the lateral geniculate body, globus pallid liS, and post,
rior limb of the incemal capsule.
D. The ant.erior cerebral artery (Figure ,3-2) supplies rhe medial surface of the hem 5p.h~r~fr01J1 the frontal pole to the pariero-occipital sulcus.
. . -
i. The anterior cerehral artery irrigates [he paracentral lobule, 'which contains d· leg .. foot area of the motor and sensory cortices.
2. The anterior communicating artery connects the twO anterior cerebral arterie t It is 'th~ most c.Qrnm.or.ujte_o(~n~urysm of t11e circle of \Villis, \yhich may cau: bitemporal lower quadraJ:ltanopia. ,
~ "'-_. ---- .- .-~ .' " ....
3. The medial striate arteries (s~e Figure 3,1) are the penetrating arteries'of rhe ar. terior cerebral artery. They supply the anterior portion of the putamen and cau date nucleus and the anceroinferior parr of the internal capsule.
E. The middle cerebral artery (see Figure 3,2) ,
i. This artery supplies rhe 'lateral com·exity of the hemisphere, including: a. Broca's and \Vemicke's speech areas b. The face and ann areas of the moror aqd sensory cortices c. The frontal eye field
B
I Anterior cerebral artery _____ -'I Mid~le cerebral artery F·:·:·::;·,·~:)::~ Posterior cerebral artery ••••• !. A
Figure 3·2. C"rticaJ territories (Jf the three cerebral ;merics, (A) Lmcral aspect oi the hemisphere. Most (l: [hc latcral Ct)Il,· .. ·:-;ity is supplieJ by the l1liJll/e ccrehml ancry. (lJ) Medial amI inferior <l~pe([s of the hemisphere TIH: ;1n(crit'f (cr .. +r,d :tnery ~lIrrlies the medial 5I1r(;1(e of rhe h(,/lli.~phere frolll the l:\lnin:1 tcrrnin;dis en the cuneus. The I',':r.:rio( (c_rchr,d ;H!UY ~lll'plics the ,vistl,d c(lrr.('~ ,',:ld rl;c I'f':.rrrior illfcri(l( ~lIrrl"" "I d'.",rc'!I!;)') r;)ll()hc , (\1(\11rc·J f(ni{l 1 (lfH!tlf)'.;~ ;'::!''''~'ijt('d j:) :-'1(il)~qr;1 f ,\:1\, :l ~'/',,:I[:(''',;' d·,: ,\1(}; ff' '
2. The lateral :;triate arteries (Figure 3-3) are rhe penetrating branches of rhe middle cerebr."l "reery: Ther me the areeries of stroke, and they supply the· internal.
·Il. The vertebral artery is a br.lOch of the suFclavi;lIl llrtery. Ie gives rise to [he anterior spinal artery (see 1) nnd the posterior inferior cerebellar artery .(PICA), which supplies the dorsohueralquadnlOt of the medulla. This quadrant includes the nucleus ::unbiguus (eN IX, X. ~md Xl) and the inferior surface of the cerebell.um.
B. ·The basilar artery is fonned by the n .... o vertebral mteries. It gives rise to the following arteries.
:1.. . The paramedian branch.es of the pontine arteries supply [he base of the pons, which includes the corticospinal fibers and the exiting root fibers o(the abducent nerve· (eN Vo. .
2. The laoyrinthirie artery <1rises·fr~m· the basilar artery ·in 15% of people. It arises from the anterior inferior cerebellar artery in 85% of people.
3. The anterior inferior cerebellar artery (AICA) supplies the caudal lateral pon·tine tegmentum, including CN VII, d;e spinal trigeminal tract of eN V. and the inferior surface of the cerebellum.
4. The supe'rior cerebellar artery supplies the dorsolateral tegmentum of the rosa-al
Medial side
Anterior cerebral artery -1111 Caudate nucleus ",
Lateral ventricle "
Posterior cerebral artery -
Subthalamic nucleus - - - - - - --
Substantia nigra - - - ~ ~
Basis pedunculi - - ~ ~
D Anterior choroidal artery - -'
....:......;~--',
D , Penetrating branches
,/ of middle cerebral artery (lateral striate arteries) ':
_,- Internal capsule
" Putamen
_,-Globus pallidus
1////1 _-Miqdle
cerebral artery
__ ~ Caudate nucleus
___ - - - Lateral ventricle
~ fiiij - - - Posterior
cerebral artery
- - - - - - - - - Optic tract
'- - - - - - - - - - Amygdala
J:1gure 3-3. COHlnal section through {he cerehral helllisphere at the le"e1 of the internal c:1psule and thalamw. ~h()\\'ing the maj(lr vascular rcrriwrics.
18 Chapter'3 ........................................................ -........................................ , ................................................................................................ . rans (j.e., rllsrrnl to the motor nuclells of CN V), the sureric.)r cerebdbr ~JlIn the superior ~urfric~ of [he cerel--ellulll nnd cerebellar nuclei. m1d [he cc.'lChlear nuc
5. The posterior cerebral a~tery (sec Figures 3-1 t 3-2. and 3-3) is connected to .carotid artery through the posrerior communicacing artery. It provides the r jor blood supply to the midbrain. It also supplies the thalmnus. bteral nnJ r dial geniculate bodies, and occipital lobe (which includes the \'isual cortex r, die inferior surface of [he temporal lobe, including the hipl-"ocampal fonnntio Occlusion of this artery results in':1 contralateral' hemianopia withmacu sparing.
IV. THE BLOOD SUPPLY OFTHE INTERNAL CAPSULE comes primarily f~om the I eral striate arteries ofthe middle cerelmll artery and the anterior choroidal artery.
V. VEINS OF THE BRAIN':
A. The superior cerebral ("bridging") veins drain into the superior sagittal sinus. Lc: eratiOil results in a subdural hematoma.
B. The great cerebral \'ein of Galen drains the deep cerebral veins into the straight sim
VI.YENOUS DURAL SINUSES_.
A. The superior sagittal sinus receh'es the bridging veins, and through the arachne \·illi, the cerebrospinal fluid (CSF).
B. The cavernous sinus contains CN III, IV, V-I and V-2, VI, and the postganglionic syr pqthetic fibers. It also contains the siphon of the internal carotid artery (Figure 3-4).
VII. ANGIOGRAPHY
A. Carotid angiography. Figures 3-SA and B sho~v the internal carotid 2rrery, anreric cerebral artery, and middle cerebral artery.
Superior sagit1al Si.1US
Cavernous parI 01 ICA
Petrosal part 01 ICA
Basilar artery
Sigmoid sinus
.......
~Ig;~ Superior cerebral veins
Superior sagil1al sinus
Branches of MCA
peA' ---
Slraight sinus
Confluence of the sinuses
Transverse sinus
iiiiiiiiiiiiiiiiiiiiiii- Veri ebr a I a r I e ry
Figure 3-4. ~Llgnctic n·~on;lI\Ccani:iogr.\II\.lalcr;l1 projccti(II). shnl\'in!~ the 111;lj<,lr \,CI)('ll'i Si!l\lV:S :lnd ;':lC: i (: S, ~) () l c: the hr i d i; i I1g \'C i II' l'l H c:r i 111: (he ~(ll'cr in r ~:\i; if(;) I \ i Ii II s. ! C .\ i, ,,',' t 1 , .,' {,,,,, l i' i '.l'."" ",. ,\! ~ . '\ : ,:.
C. Veins an~ dural sinuses. ~igur\! 3-6 S)~ll\\"S rhe int~rnal c~rebr:11 \'ein .. superior cerebral \"c~ins, great cerebml \'ein, sur~rior ophrhalmic vein, and major dural sinuses.
D. Digital subtraction angiogrnphY"See Figures 3-7,3·8.3·9, and 3-10.
. VIII. THE MIDDLE MENINGEAL ARTERY, a bmnch of the maxillary artery, e~ters {he cmnium throl,lgh [he foramen spinQSu!ll. It supplies most of th~ dura, including its cakarial porrion. Laceration resuics in epidural hemorrhage (henl<ltoma) {Figures 3-11 and 3-iZ].
Figure 3·6. Ca.rotid angiogram, \'enous'phase, showing the cerebral veins and \'enous sinuses.
Callosomarginal artery of ACA
Pericaliosal artery -j~I~li~% of ACA
Frontopolar branch -- ,
OfACA ___ ~~~~;:~ Ophthalmic artery
Cavernous ICA -----=--"'j.-r.
Petrous ICA
'.
.. .,;
.; .. -'
5:,,~'. ~=-~-~:-7-----,:;::;-~_ MCA M1 segment
~:------:------:=--- PCoM ~
Cervical ICA -----::-~~~~~~~
I I I I I I I I I t I I I
Figure 3-7. C::lwrid angiogram, I'Heral projecrion, Idcntify rhe cortical branches of the [Interior cerchr I artery (ACA) and middle ccrebral artery (?-.fCA), Folio\\' the Course of thc internal carotid <lrtcry (leA). R. Il1cmher chat aneurhms of the posterior communknring M(Cry may resulr in third,ner\,e p:lls},. TI1C par:lcelltr. ld'ulc is irrig:ltcd hy the ca\losoln:1rginal artery, Conical branches of [he ~'tCA arc tksignntcd with dots. reo!' I = p()~teri()r communicating anery, '
A"\ segment of ACA --::~i~t;~0:ts~ = ...... ,..,.,"""
Cortical branches of MCA
Lateral striate branches ofMCA
M1 segment of MCA
Cavernous part of ICA --~~~~~~::.~~£~a~~~~~~~;~..:... Supraclinoid part of ICA
Petrous part of ICA
'. . ;-:;'''I-:il)~-~--:.
,," .T .• -. '. .-.'.-. . ...
1'!!'''''---"""7-- Cervical part of ICA
Figure 3-8. Carotid angiogram, anteroposterior projection. Identify the anterior cerebral artery (ACA). mid~ dIe cerebral artery (i\fCA), and internal carotid artery (lCA). The horizontal branches of the MCA perfuse the basal ganglia and internal capsule. ACo:\i = anterior'communicating art~ry·.
Posterior choroidal arten..es
...••. --:."';7 .... -c--.-:, .. - .
PCA. P1 segment+''';''':;~~:-''''''!z
~.~BI Thalamoperforating
arteries~~~~
PCoM-===
Superior cerebellar artery~.;;;:..;:~
Basilar artery~~~~
Vertebral artery 7-:-:;;~~~~~
,t{~I~~~2:~--- Parieto·ocd'tpital b,anches of PCA
=:.~~:- Calcarine branches of PC A
=:::::;--- Hemispheric branches of SCA
~~.,.----- PICA
(:~~L====::::=---- Vertebral artery
Figure 3-9. Vertebral angiogram, lateral projection. Two S[rliClUrcs arc founJ between the posterior cerebral .: artery (PCA) and the !)up<:rior cerebellar artery: the tentorium and the thiiJ cranial nerve. PCoM = po!)terior
Figure 3,1.0. Vertebral angiogram, anteroposterior projection; Which artery surrlies the visual cortex? 11 I calcarine artery, a !::-ranch of the FO~terior cerebral arrery (peA). Occlusion of the PC";' (calcarine artery) resul in a con-cralateral homonymous hemianopia, with macular sparing. PICA = Fosterior inferior cerebellar aLter
t Diploe
t .. ,
I I I
1 FIgure 3-:1.1, An epidlJral hematoma rcsults (mill bcer;l[ion ofthc l1lidd!.: I1lcnil1~~·.d artery. Arterial blccl; 1 in" into the cpiJur"I.\p;ICC forms" hicol)\'cx clot. The ch:,\ic "I\lci,l inlc\,,;1\" i~ sccn in 50% o( C;lses. Skull (r;l( ru;c:~ arc u~II;llly ((lund. Epidllr;tl hC:ll1:lI()fn:l~ ri1rcly cr(\,;s .,l)lur;d lillt''; i1\('i,li"ICJ with pUIlli\\jcl[) ;'(:"11 (""hi;. I AG, Tong KA: HW\{!I)(,{jl-: 1(/ ,"! '!nllf,:r!;,·f,. . ;;f"'" (,;:,: "~",'I c;~ l.",. '!" ". i ;):
Figure 3-j.2. .-\ subdural hem,l[oma (SOH) results from lacerated br-idging yeins. SDHs are frequently accomranie..:i by traumatic :5ubarachnl)iJ hemorrhages and cortical contusions. Sudden deceleration of the head causes tearing of the superior cerebral veins. The SOH ~xtends o\·er the crest of the convexity into the interhemisrheric fissure. r-Ut does not cross the dural attachment of the falx cerebri. The clot can be crescent-shaped. biconyex. or multi loculated. SOHsare more common than epidural hematomas. SDHs always cause brain damage. (Reprinted with permission from Osbum AG. Tong KA: Handbook of Ne1!roraciiology: Brain and Skull. St. Louis. ~f05by. 1996. p. 192.)
I. TH E' N EU RAL TUBE (Fi,iure 4· i) gi ~'es rise ro the cen tra I ne,,'ou s -s l'stem (eNS) [i., I brain and spinal cord}.
A. The brain stem and 5Final cord ha\'e;
:1.. An alar plate that gi\'es rise to the sensory neurons
2. A basal plate that gi\"es rise co the motor neurons (Figure 4.2)
B. The neural tuce gives rise to th:ree primary vesicles, which develop into five sel ondary vesicles (Figure +3).
C. Alpha.fetoprotein (AFP) is found in the amniotic r1uid and maternal serum. Ie is a indicator of neural tut-e defects (e.g., spina binda, anencephaly). AFP levels are n duced in mothers of fetuses with Down syndrome.
Surface ectoderm ,":
/
Dorsal root ganglion
Alar plale (sensory)
Sulcus limilans
Basal plate (motor)
I I I , 1 I I I I I I FJgure 4-:1.. [X:\·e!nprntnt (J( the ncural whe and cre.'r. The abr pl.irc- !;i,'cs: ill' (.' .\cr,,()! llllurol1.< .. Th . : ,)';
Development of the NelVous System 25 ...................... : ................................ ~ ..................... ~ ........................... : .... :; ....... -.. -.... : ..................................................... ; .................. : ...... .
. Roof plate (ep.endymallayer)
Pial blood vessels -----.
fourth.ventricle ---.,
SSA nuclei ----+J.GSA column ---4~
SVA column ---"""\
GVAcolumn--
!3VE column ----
SVE column ------
GSE column - __ _
Floor plate -----
~----Tela choroidea
Semicircular . ducts
Ampullae
-1---- Cochlea
1"'--___ . Skin
g-- Taste bud cell of tongue
Somatic striated muscle ---~lllr (tongue)
-1--- Visceral epifhelium ~.J--l,-.l.:JC!.1
Branchial striated muscle -------~~lll (larynx)
'----- Smooth muscle
Figure 4-2. The brain stem showing the cell columns derh·ed from the alar and basal plates_ The seven cranial nen-e modalities are shown_ GSA. ::: general somatic afferent; GSE = general somatic efferent; GVA = general dsceral afferent; GVE = general \-isceral efferent; SSA ::: special somatic afferent; SVA = special visceral afferent; SVE = special visceral eff~rent. (Adapted with pennission from Patten BM: Hwnpn Embryo log)' , 3rd eJ. New Yo~k, McGraw-Hill, 1969, r- 298.} . ':
II. THE NEURAL CREST (see Figu;~ 4-1) gi\'es rise to:
A. The peripheral nervous system (PNS) [Le., peripheral nerves and sensory and autonomic ganglia}
B. The following cells: .. '
i. Pseudounipolar ganglion cells of the spinal and cranial nerve ganglia
2. Schwann cells (which elaborate the myelin sheath) /
3. Multipolar ganglion cells of autonomi~ ganglia
4. Leptomeninges (th~ pia-arach.noid) envelop the brain and spinal cord
5. Chromaffin cells of the suprarenal medulla (which elaborate epinephrine)
6. Pigment cells (mclanocytcs)
7. Odontoblasts (which elaborate predentin)
B. AOfticopulmonary septum of the heart
sss
Highlight
.1Ia
Dar ·n • ..
26 Chapter 4 I -.... ~~.;~:.;;J::~ ........... ' ................... -: ... -.............................. ;J;::::~-:;:~-......... ~~:.;;.~:;;;~;;~~:.:;;:............... I
vesicles vesicles . Walls Cavities
Telencephalon Cerebral hemispheres
Lateral ventricles
--r;- F~rebrain L Diencephalon __ -+-1-(prosencep.hcilon) ~-- Thalamys Third
:1.0. Skeletal and connective tissue components of rhe pharyngeal arches - .
Ifl. THE ANTERIOR NEUROPORE. The closure of the anterior neuropore gives rise to rllamina renninalis. Failure to close results in anencephaly (i.e., failure of the brain to & \·e!op). ,.
IV. THE POSTERIOR NEUROPORE. Failure to close results i~ spina bifida (Figure +4
VI. MYELINATION ~gins in the fourth month of gestation. Myelination of the corticospinnl tnlcrs is norcornpleted until the end of the second rostnaml yeM, when the tracts become function.,l. Myelination in the cerebral a~sociation cortex continues into the rhirJ decnde.
A. ~lyelination of the eNS is nccon,p1i~hed by,oligodendrocyt~s, which ;-Ire not found in the retina. '
B. ~{yelination of the PNSis accomplished by Schwann cells.
VII. POSITIONAL OHANGES OF THE SPINAL CORD
A. In the ~ewborn, the conus medullaris ends at the third lumbar vertebra (L,3).
B. In the adult, the conus medullaris ends at L,l.
VIII. THE OPTIC NERVE AND CHIASMA are derh'ed fron) the diencephalon. The optic nerye fibers OCCUP): the choroid fi~sure:F.a.ilure of this fiss.ure ~o .close results in coloboma iridis. ,
IX. THE HYPOPHYSIS (pituitary gland) is derh'ed from t\\'o embryologic substrata (Figures +5 and 4,6). . ,
A. Adenohypophysis is d~rh'ed from an ectodennal diverticulum of the primitive mouth ca\'it)" (stomodeum), which is 'also called Rathke's pouch. Remnants of Rathke's rouch may gh-e rise co a congenital c)'stic rumor, a craniopharyngioma.
B. Neurohypophysis de\'elops from a \'entral evagination of the hypothalamus (neu, roectoderm of the neural tube).
X. CONGENITAL MALFORMATIONS OF THE CNS.
A. Anencephaly (meroanencephaly) results from failure of the anterior neuropore to close. As a result, the brain does not de\·elop. The frequency of this condition is 1:1000.
, . Third ventricle
Pars tuberalis of adenohypophysis --t---'--....
Adenohypophysis (anterior lobe) --~~,.-\-J
Infundibulum of hypothalamus
Diaphragma sellae
Pars intermedia of anterior lobe
-+--f-''F.+-- Neurohypophysis . (posterior lobe)
Dura
Sphenoid bone
Craniopharyngeal canal Remnant at Ralhke's pouch
Figure 4-5. Midsagittal section thwlIgh the hypophy~is :IIlJ sella turcica. The :lJcnohypophysis, including the p<Jrs tuhcralis and pars intermedia, is ,ll:ri\'ed (rom Rathke's pouch (oroecwderm). The neurohypophysis arises frelln the infundihulurn ()f the hyp'llha!amus (m'ur"l'clOJcnn).
Figure 4-6. ~Hdsagittal section through the brain stem and diencephalon. A craniopharyngioma (arroU'! lies suprasellar in the midline. It compresses the optic chiasm and hypothalamus. This tumor is me most corr I mon supratentorial tumor that occurs in childhood and the most common cause of hypopituitarism in childrer This is a Tl,weighted magnetic re..-onance imaging scan.
Figure 4-7. Arnold·Chiari mal({lrlll:lti()Il. Midsagittal s~ctio~,. (A) Normal cerebellllm. fourth \'cntricle. an, brain stem. (B) Ahnormal ccrchcllullI. (ollnh \'cntricle. _lnt! hrain stem 5ho\\'ing the COllllllon congcnital anom ali(:~: (I) be;lking o( the rcclill plate. (2) aqlleJlIccal ~(cn(lsis. (3) kinkin!,: and tr:1m(omlllinal herniation o( th rncdldh into the \"(.:rtchral cana\. ;J1l,1 (4) hcrni:ltiol1 ;lId Ilmnlling of (he ccrchclhr \'eflnis into rhe ,'crtcbr;l cZln;d. An ;lccnrnpanyiTlf! f11("llillgolllyclncI'!" ii, (",1'!:1\,:;, (f(q)ril~i('l! \\1[;, : ,-,,";"')'.", ({(;In Fiy if""
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Development of the Nervous System 29 ...................................... ~ .................. : .. : .................................. __ ....... : ......... - ........ ~ ......................................................................... .
Corpus callosum Polymicrogyria
Superior s'agittal sinus
Straight sinus
,.~"'\-'t---- Confluence of Lateral ventricle -H;f.~-----:":--I--I--':""- sinuses
Massa intermedia \~t-=~::::::~;!-{-
Third ventricle ----"~~~----?- +----------,fH- Cerebellar vermis
Pons --''<''-':='''+-i- , ,
--->-+--i'-l-7~- Posterior fossa cyst
Medulla -->t'r'.-
Figure 4-8. Dandy-\Valker. malfdrmation. ~{idsagitcal section. An enormous dilation of the fourth ventricle results from failure of the foramina of Luschka and Magendie co open. This condition is associated with occipital meningocele. elevation of the confluence of the sinuses {torcular Hero"phili}, agenesis of the cerebellar \'ermis. and splenium of the corpus callosum. (Rerrinted with permission from Dudek RW. Fix JD: BRS Embryology. Baltimore. \Villiams & \Vilkins. 199i. r. 9i.) .
B. Spina bifida results from failure of the posterior neuropore to form. The-:defect usually occurs in the sacrolumbar region. The frequency of spina bifida occulca is 10%.
C. Cranium bifidum resuirs from a defect in the occipital bone through which meninges, cerebellar tissure, and the fourth \·~ntricle may herniate.
/
D. Arnold~Chiari malformation (type 2) has a frequency of 1:1000 (Figure 4-7).
E. Dandy~ \Valker malformation has a frequency of 1 :25000. It may result from riboflavin inhibitors, posterior fossa trauma, or viral infection (Figure 4-8).
F. Hydrocephalus is most comnl9.nly caused by stenosis of [he cerebral aqueduct during de\'elopment. Excessive ce'reh~osrinal fluid accumulates in the ventricles and subarachnoid space. This condition may result from maternal infection (cytomegalovirus and toxoplasmosis). The frequency is 1: 1000. .
G. Fetal alcohol syndrome is the most common cause'of menml retardation. It includes microcephaly and congenital heart Jisease; holoprosencephaly is the most severe manifestation.
H. Holoprosencephaly resuJts frolll failur~ of miJline cleavage of [he embyonic forebrain. The telenceplalon contain's a singllim ventricular c",·ity; is seen is trisomy 13 (Patau syndrome); the corpus callo$lIlll may be nbsclH; holoproscnccphaly is rhe most severe manifestation of the fetal nlcohol syndrome.
I. H ydranencephaly results from biiarcral hcmispheric infnrction secondary to occlusion of the carotid Clrtcries. The hClllbl'lH.'rcs arc replaceJ by hugely dilated vcntricles.
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Neurohistology I I 1 I I. NEURONs 'are classified by the~11ul"'!1l:-er of processes (Figure 5#1).
A. Pseudounipolar neurons are located in the spinal dorsal roOt ganglia and sensory g I glia of cranial neIves (eN) V, VII, IX, and X.
Olfactory
Dendrite zone
Axon origin ____ _
Axon
T Telaxon
1.
Sensory (receptor) neurons Motor neuron
Auditory Cutaneous
Synaptic endings (boulons terminaux) Nerve endings in muscle (myoneural junction)
Figure 5-:1. Types of ncn'c cells. Ol(ac(ory ncurons flrC hirobr and lllllll\'dinarcd: Auditory neurons arc hil I;)r nnJ myelinated. Dorsal root ganglion cells (cllt,mcous) are r~clldotll)ipolnr ,lnd myelin.ncd. Motor ncur< ;He 1l111ltipo/;lr :lnd rnr(.'lin;l[cd. ATTOW5 indicntc input through tile aX0HS o( p{her I1ClIrnllS. Nervc cclls ;"Ire eh ;IClcri:cd hy the prC\('I)CC o( Nis~1 ~uhst;mcc ;I1\J HIlIg" cndopl;\<mic r(,{jculu\I, (H",jifil"d with l'l'fmi"sic:ll (. (';\rlP'fiier )I.·if1. (~t;[i')):) illl!1on NCllrol/rlOlo'71Y H:ilrim()[c, \'1/111;.1111' {". \Vii',·: I .,'., 'i" \
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Neurohistology 31 ...... --: ..................................... ~ ....................... , ............................................................................................................................................ . . '. .." . 'B~ Bipolar n~uron~ nrc found in ,he co~hb\r anj \'c:\tihuJar gangli~ I.lf eN VIII, 'in the
I.)lfac[l.)ry nerve (CN I), ;lIlJin the rerina.
C. Multipolar neuron:; me rhe lmgc$t l'l.."\i'lIbdt)~\ I.\f nerve cells in rhe nervous sY:'tem. This ·grl.'lIP incluJes motor neurolls, ncuronsl.\f the autonomic'nervous sY:'tem, intcmeUn)llS, pyramidal cells of the cerebrcll cortex, an~ Purkinjc's ce,lIs of the cerebellar correx.
D. There me approxim;l~e1y 1011'n'cufoll$ in th~ r.rain and approxim:ltely IOl~' neurons in rhe l:teocor~ex.
II. NISSL SUBSTANCE is characteristic of neurons. It consists of rosettes'of polrsomes apd < .. "Iugh endoplasmic reticulum; therefore, it has a role in protein symhesis. Ni~.sl subsmnce :~ found in the nerve cell body (perikaryon) ~nd dendrites, not in the axon hillock or axon.
III. AXONAL TRANSPORT mediates the intracellular distribution of secretory proteins. or:;.lOelles, and cytos,keletnl elements. It is inhibited by colchicine, which depolymerizes mi- . .:r\.'lcut-ules.
," _ .... _ J • , •
A!~' Fast'an'terograde axonal transport is re'sponsible for trarisporti~g all newly synthesi:ed .' m~i11brarlOus organelles (vesitles) and precursors of neurotransmitters. This process
occurs at the rate of 200 to 400 mm/day. It is l!1ediated by neurotubules and kinesi.!'t. \Fast transport is neurotubule-dependem.} '. .::.=.:",.-« ~""-'- '''" .... , ... 0,,,.
,-) ----.-~"--~----" '" '-,' '-, .
<~,.~·SlO\~._~!l,~~~~g~?~J.~!l~.P..9SCis responsible for ,rransporting fibrillar cyroskeletal and ~. rroroplasmic elements. This proce6s occurs at the rate of 1 to 5 mm/day.
C.F~st retrograde transporfreturns used materials from the axon tenninal to the cell body for"'de-g"faaatiOi1'anci'recycling at a rate of 100 to 200 mm/day. It transports nerve growth factor, neurotropic viruses, and toxins, such as herpes simplex, rabies, poliovirus, and tetanus toxin. It is mediated by neurotubules and dynein.
IV. WALLER IAN DEGENERATION is a~grade~d~~.e.t:adon characterized by the dis;Fpearance ofaxons and myelin sheaths and the secondary proliferation of Sch\\'ann cells. It occurs in the central nervous system (CNS) and the peripheral nervous system (PNS).
',.. V. CHROMATOLYSIS is the result of retrograde deg~neration in the neurons of the CNS
3,Ild PNS. There is a loss of Nissl substance 'after axoromy.
VI. REGENERATION OF NERVE CELLS .. /
A. eNS. Effective regeneration does not occur in the eNS. For example, there is no regeneration of the optic nen'e, which is a tract of the diencephalon. There are no basement membranes or endoneural investments surrounding the axons of the CNS.
B. PNS. Regeneration dq~s .. oc~udn the PNS. The proximal tip 'of a severed axon grows into the ei1doneuraltube, \Vh-ich consists of Schwann cell basement membrane and endoneurium. The axon sprout grows at the rate of 3 nun/day.
VII. GLIAL CEllS nre the nonnellfnl cells of the neh'ous system.
A. Macroglia consist of astroc)'tes and oligodendrocytes . . :t. Astroc)'tes perform the following functions:
a. Thcy project foot p'roccsses that envelop the basement membrane of capillaries, neurons, and synapses.
b. Thl'y form the external and internal g~ial-limiting membranes of the eNS. c. They playa role in the metabolism of certain ncurotransmitters [e.g., -y
I 32 Chapter 5 .................................................................................................................................................................................................................
I d. Ther butrc:r the pomssium cOllcemr:ltion of the e~qr:lcelllll:u space. e. Th~y fl\pllJ;IJnLs91Q in Jmfinged.areas of the bmtl~ (Le .• nsrrogliosis). f .. Ther comnril-~:lJ.fi~~~ll~~!1'~~c_i.~.!.~J.~E~t~~~1.~~J, which is a marker (\.'r ~ I
tr~'cyte$.
g. They cOllC<lin glutamine synthetase. another biochen1ical m~uker t~'r ~1Stn.-'Cn{ h. ~t;"\r l-e identified with monoclonal antibodie~ (e.g.! AZB j ). "
2. Oligodendroc'·tes are the myelin-((lrming cells of the eNS. One oligodendmcy can myelinme as m:my ClS 30 a;,:o11$.· . . . '-"---_.,.-_ .. "
B. Microglia nrise twm moi1Ocyres and function as the scavenger cells (rhagocyres) ( 1 the eNS.
c. Ependymal cells are ciliated cells that line the central canal and "enrricles of rh brain. They also line the luminal surface of the' c-horoid plexus. These cells produc . cerebrospinal fluid (CSF). .. . .
D. 'Janycytes are ~~0.9.i~~depen.~rill~1 c~H:i that contact cnpillaries and ne~rons. TI1ey med ate cellular traruron bet\\;een ~he \'enrricles and the neuropil. They rroject to hyrotha: amic nuclei that regulate the release of gonadotropic honnone from the adenohypophY$i:
E. Schwann c~lls are.deriyed (ro11.~.~he neural crest. They are tJ1e myelin-forming celis. c the PNS.~ncell£g~ul;\:~JiI}~r~ (mJYR1~.e inre61gde. Schwann cells itwe5 all myelinated and unmyelinated axons of the PNS and 'ire separated from-each othe by the nodes of Ranvier.
VIII. THE BLOOD-BRAIN BARRIER consists of the tight junctions of nonfenestrated en dorhelial cells; some authorities include the astrocytic foot processes. Infarction of brair tissue destroys the tight junctions of endothelial cells and results in vasogenic edema which is an infiltrate of plasma into the extracellular space.
IX. THE BLOOD-CSF BARRIER consists of the tight junctions between the cuboidal ep· ithelial cells of rhe choroid plexus. The barrier is permeable to some.circulating repride: (e~~:~.~~~~_I~I1) aI1~ plasma proteins (e.g.; prealburi11fi). " --:
X. PIGMENTS AND INCLUSIONS
} ; . . ,; .'-
... ..,.. ..
A. Lipofuscin granules are pigmented cytoplasmic inclusion's that commonly accumu· late wiih aging. 1lley are considered residuaIJ~c:>dies that are derh-ed from lysosomes .
..... -.--,--~.- . . ... .
B. Melanin (neuromelanin) is blackish intracytoplasmic pigment found in the subsran· tia nigra and locus coeruleus. It disappears from nigral neurons in patients who h3\'( Parkinson's disease.
C. Lew)' bodies are neuronal inclusions that are chaf(lcteristic of Parkinson's disease.
D. Negri bodies are intracytoplasmic inclusions rhm me pathognomonic of rabies. ll1ey arc found in the pyramidal cells of the hippocampus Clnd the Purkinje cells of the cerebellum.
E. Hirano bodies (lrc inrr;lIieurol1al, eosinophilic, roJlike inclusions that arc found in the hippocampus of patients with Alzh~iXt.:'t~r.'s discnse.
F. Neurofibrillary tangles consist of intracytoplasmic degenerated neurofilaments. They mc seen in pnrients with Alzheimer"s disease.
G/;~Cowdrr type A inclusion bodics arc'intral1ucidr ancillsions th;l( arc found in neurons and glin in h£.TCS Sil"l~ie~x··cilCcph;-·d i (is.
XII. TUMORS OF THE CNS AND PNS are shown in Figure 5~2.
A. One~third of brain tumors are metasratic, and two~thirds are primary, In metastatic rumors, the primary site of malignancy is the lung-in 35% of cases, the breast in 17%, in the gastrointestinal cract in 6%, melanoma in 6%, and the kidney in 5%.
B. Brain rumors are classified as glial (50%) or nonglial (50%).
C. According to national board questi.ons, the five most common brain rumors are:
i('{;Iioblasto~a "muldfc)rme-;-rh{nll)st common and most fatal type "-... ----..... -.- .... ~.~~-.- .. ----'" ........ " .-,-
2.,. Meningioma,- a benign noninv<lsi\'e tumor of the falx and the convexity of the hemisphere .~,'. - - .--~-.. ~.~........... -
3. Schwannoma, a benign periph~r;ll rumor derived (rom Schwann cells
~:- Ep~~d ;:~~ma. which is (ound in rhe ventricles and accounts (or 60% of spina I cord "'g1T6mas--' . .
'-' ....... -- ---.
5._~ Med~floblastoma: which is the ~«:LOnd mc;>sl: common posterior fossa tumor seen in'chi-Idren and may metastasi:e through the CSF craces
XIII. CUTANEOUS RECEPTORS (Figure 5~3) are divided into cwo large groups: free nerve endings and encapsulated endings.
A. Free nerve endings are nociccprors (,,_lin) and thermorecepcors (cold and hent).
B. Encapsulated endings are touch H.'Ct.'prors (Meissner's corpuscles) and pressure nnd vi~ bration rec<:ptors (Pacininn corplIscks).
I
I 34 Chapter 5 ............................................................................................. ~::~~~~;~:~~................................................................................... I A . derived from arachnoid cap cells and represent the second most
Germlnomas • germ cell tumors that are commonty
seen in the pineal region (>50°.,) • overlie the tectum of the midbrain • cause obstructive hydrocephalus due to
aqueductal stenosis .' • the common cause of Parinaud's syndrome
Brain abscesses --'---.... • may result from sihusitis,
mastoiditis, hematogenous spread
• location: frontal and temporal lobes. cerebellum
• organisms: stre~tococci, • staphlococci. and
pneumococci • result in cerebrat edema'
and herniation •
Colloid cysts of third ventricle • comprise 2% of intracranial gliomas • are of ependyr:-:al origin • found at Ihe in:erventricular foraminia • ventricular obs!ruction results in increased
intracranial pressure, and may cause positional headaches, ~drop attacks; or sudden dea!h
8 Choroid plexus papillomas '. historically benign • represent 2% of the gliomas
common primary intracranial brain tumor atler astrocytomas (15% • are not invasive; they indent the brain; may produce hyperostosis • pathology: concentric whorls and calcified.~sammoma bodies • location: parasagitlal'and convexity --_.:. ~ ..... -. . • gender: females> men •. associated witli neuro~ibroma~0.sis-2 (NF·2)
Astrocytomas • 'represent 20°\' of the glioma9 • historically benign • diffusely infiltrate the hemispheric white matte • most common glioma found in the posterior
fossa of children
ro-+--- Glioblastoma multiforme
Oligodendrogliomas • represent 5~;' of all
the gliomas • grow slowly and !'Ire
relatively benign •
.• represents 55% of gliomas • malignant; rapidly fatal
astrocytic tumor • commonly found in' the frontal and
temporal lobes and basal ganglia • frequently crosses the midline via the
corpus callosum (butterfly glioma) • most common primary brain tumor • histology: pseudopalisades,
perivascular pseudorosertes
• most common in the frontal lobe .• calcification in 50% of cases ~ cells look like "fried eggs· (perinuclear ha!os)
Craniopharyngiomas • represent 3% of primary brain tumors • derived from epithelial remnants of Rathke's pouch
• one of the most common brain tumors in patients < 2 years of age • location: suprasellar and inferior to the optic chiasma • occur in decreasing frequency: fourth, lateral, and third ventricle • cause .bitemporal hemianopia and hypopituitarism
• calcification is common
J Cerebellar astrocytomas' Pituitary adenomas (PA) • most common tumors of the pituitary glane
• CSF overproduction m:y cause hydrocephalus ~
/[ . -:-6enign tumors of c~il~hood with ~ood prognosis ; .~~Sl S2-~gCLPJlti!.~trl(~_1mE~:~.n'!IjU!J:l9r . _---<:---_
• contain piJocy.ic astrocy1es anC! Rosenthal fIbers ~ • prolactinoma is the most common (PA) • derived from the stomodeum
(Rathke's pouch) .• • represent 8% of primary brain tumors
.;...--. represent a primitive neuroectodermal tumor (PNEn
• second most common posterior fossa tumor in children
• responsible for the posterior vermis syndrome • can metastasize via the CSF tracts • highly radiosensitive
Hemangioblastomas • characterized by abundant capillary blood vessels
and foamy cells; most otten found in the cerebellum • when found in the cerebellum and retina,
may represent a part of the von Hippel·Linc!a.usyndrome • 2% of primary intracranial tumors;' 10% of posterior fossa
tumors
• may cause hypopituitarism, visual field defects (bitemporal hemianopia and cranial nerve palsies CNN III, IV, VI, V·1 and V·2, and postganglionic sympathetic fibers to the dilator muscle ot the iris)
Schwannomas (acoustic neuromas) • consist of Schwann cells and arise from the
veslibular divis:on of CN VIII • compromise approx. 6% of intracranial neoplasms • pathology: Antoni A and B tissue and Verocay bodies • bilateral acoustic neuromas are diagnostic of NF·2
'----
Brain stem glioma • usually a benign pilocylic astrocytoma
Figure 5-3. Three important cutaneous receptors. free ner\'e endings·mediate pain and temperature sensation.0eissner corpuscles of the dermal papillae mediate cactile t\\"o-p~ini: discrimination. Pacinian corpuscles of the:dermis mediate touch, pressure, and vibration sensation.
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6 'Spinal Cord·
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I I I I I
I. GRAY AND WHITE COMMUNICATING RAMI (Figure 6.1) I A. Gray communicating rami contain unmyelinated postganglionic sympathetic til"'er
They are found at all le\'e1s of the spinal cord.
fibers
B. \Vhite communicating rami contain myeliI)ated preganglionic sympathetic tiber. The\' are found from T~ 1 to L~3 (the extent of the lateral hom and the inrermediolat eral ~ell column). .
II. TERMINATION OF THE CONUS MEDULLAR.S (see Figure 2-1) OCcurs in the ne\\ born at the le"el of the bod\' of the third lumbar "errebra (L~3). In the adule, it Occurs ,; the le\'e I of the lower borde; of the first lumbar vertebra (L-l).
Paravertebral ganglion (sympathetic trunk)
Prevertebral ganglion
•
Alpha motor neuron of ventral horn (GSE)
Figure 6-:1. The (our (unctional C(1lOr()ncnt.~ of the thoracic .\pin;ll ner\'(,: gCl1er:d \'jsccr;l! :lffcrcl1t (GVA gcncr<ll s()m~Hic ;dfcr<:nr (C;:;;\). J~cf)cr;d 50rnatic efferent (GSE). :md ~;l"Ill'r;tl \'i.<cer;il d(l'IC"H « iVF). l'n'pri
! . '(] I TI I ' .. . , . ClTli',c, CliL1Il('()IJ.';, ,:Iflr \'I\'~"(,ii (l·.l'", flfC'> fire:~, )01\'11. ,,"" ;:;:i.',(' :':".:: I) "~1\'(I'.lil: I "I:;" II;, ;., " .. " iiI', '\
III. LOCATION OF THE MAJOR MOTOR AND SENSORY NUCLEI OF THE SPINAL CORD
·A. The ciliospinal centt!r of Budge, (rom C-8 to 1',2, mediates the s)'mpathetic innex-va· til.:'ll1 of che eye.
B. The,intermediolateral cell column, from C-8 to L-3, mediates the entiresympatheric innernlrion l)( rhe bl.'ldy.
C. The nucleus dor~aHs of Clark, from C-8 [0 L;3; gives rise r:o the dorsal spinocerebel, br tmer. ..' .
D. The parasympathetic nucleus, {rorp $-2 to S-1.f
E. The spinal accessory nucleus, from C-l r:o C·6
F. The phrenic nucleus, 'from C,3 to C,6
.IV. THE CAUDA EQUINA. Motor and sensory roots (L,2 r:o Co) that are found in the subarachnoid space below the conus medullaris form the'cauda equina. They exit the \-errebral canal through the lumbar intervertebral and sacral foramina.
V. THE MYOTATIC REFLEX (see Figure 6·1) is a monosyr:taptic ~nd. ipsilateral muscle stretch reflex (MSR). Like all retlexes. the myotatic reflex has an afferenrand an efferent limb. Interruption of either limb results in .areflexia. -
A. The afferent limb includes a muscle spindle (receptor) and a dorsal root ganglion neu·
B.
C.
ron and its Ia fiber.
The efferent limb includes a veil.'tral hom motor neuron thut innervates striared muscle (effector).
The four most commonty tested MSRs are listed in Table 6-1. ",-:
p,.r. __ ".'~:; '3 nsr.
1 I
7 I I I
Tract$ of the Spinal Cord
I I
. I. INTRODUCTION. Figure 7-1 sho',:s the·as·cending and descending tracts of the srina cord. TI,;S chap ter CO\·,,, I,'ur of the maj<'rtmw. I
II. DORSAL COLUMN-MEDIAL LEMNISCUS PATHWAY (Figure 7-2; see also Figurt 8-1) I A. Function. The dorsal column-mediallemniscus'pathway mediates tactile discrirnina.
tion, yie-ration sensation. fonn recognition, and joint and muscle sensation (consciou: I proprioception).
B. Receptors include Pacini's and Meissner's tactile corpuscles, joint: receptors, muscle spindles, and Goigi tendon organs. I
C. First#order neurons are located in the dorsal root ganglia at all levels. They project axons to the spinal cord through the medial roqt entry zone. First-order neurons gin rise to:
:1. The gracile fasciculus from the lower extremity
Ascending tracts
Gracile fasciculus "
Cuneate fasciculus
Dorsal spinocerebellar tract
Lateral spinothalamic tract
Ventral spinothalamic tract
Descending tracts
Lateral corticospinal tract
Hypothalamospinal tract
Rubrospinal tract
VestibulospInal tract
FIgure 7·.1. The rn;1jor ;i:'C"" dinc: ;Int! descendil)l; 1': It hll"; ,\ .. , p{ rh<: .~pin;d c(lrd. The :1:;('·n<i::1,l! .'<:n)('I~' :r;iU' ; \ i:"~ :' J i 0 \ \ '1') '" 1\"\ I t'\ ,'; l c (c I ;\t 1 c.l : h ,. \ ;, 'C (" \ \ [ 1: n ~: \ t :', i \. : r .; ~. '(. (" :';-',' : ~ ~ \;., ! 1 , : \ i ~ I \: I
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. ".~ . , ..• ..;:; ... . .
Trc;tcts of the Spinal Cord 39 . . . ........................................................................................................ _ ...... _ ....................................................................... , .................... -
Thalamus ~-----f1:::L,/.A~th..L
Internal capsule ----1~~:-lr-++_ff*
Lentiform nucleus ---~"(,
Trigeminal nerve ----___ _
Nucleus gracilis
N ucl eus cun ea tu s -------,,4----:'
Internal arcuate fibers (neuron II) ------~--.-/
Cuneate fasciculus
Dorsal root ganglion cell
Postcentral gyrus
,..-------- Leg area
::::....---- Trunk area
""":;::"'"+-- Arm area
Head area
Face area
Ventral posterolateral nucleus of thalamus (neuron III)
Figure 7-2. The dorsal column-mediallcmniscus pathway.llllpubcs conductcd by this pathway mediate discriminawry tactilc sense (e .. g., touch, vibration, pressure) and kinesthetic sense (c.g., posiril)ll, movemcnt). Thc d()rsal column system mediates conscious proprioccption. (Adapted with permission (rom Cmpcllter MB, SlItin J: Human Neuro(ln(ltomy. Baltimorc, Williams & Wilkins, 1983, p. Z66.)
.... ... 3. The c(,llhuemls for spinnl reflexes (e.g., mrornric reflex) I 4. The l'lx(,'lns that ascend in the dorsnl columns nnd terininme in the gracil~ .md
cuneate nuclei of the cnudnl medulla , D. Second-order. neurons' nre locnred in the gm~ile nnd c~l)ecire' nuclei of the cauLbl
medu.lIa'. They gh'e rise to nxons and inremal arcuate fibers that Jecussme and f('lrm ;l
comr~~ct fi~er ~lIndle (i.e., medinllemnisclls), The medial lemniscus ascends chnJugh 1 the cl,ntrnlatemll:-rain stem nnd terminates in the \'cntral posterolarer<11 (VPL) nu-cleus of the thabm.us. .
E. Third-order neurons are locmed in the VPL nucleus of the thalamus. They rmject I through the po5t~rior limb of the internal cnpsule to the rosrcentral gyrus; which. is the rri~aT)' som:u('isenroT)' cort~~ (Brodmann's.~.r~as 3, 1, a.i1d 2).
F. Transection of the dorsal column-inediallemniscus tract
:l. Abo\'e the sensory decussation, transection resulrs in contralateral loss of the dorsal column modalities.
2. In the spinal cord, transection resulrs in !pilateral loss of the dorsal column modalities.
I I
III. LATERAL SPINOTHALAMIC TRACT (Figure 7-3; see also Figure 8-1) I A. Function. The lateral spinothalamic tract mediates pain and temrerature sensation.
B. Receptors are free nen'e endings. The lateral spinothalamic tract recei\'es input from fast- and slow-conducting pain fibers (i.e., A-S and C, respecti\'ely).
C. First-order neurons are found in the dorsal roocganglia at all le\:e!s. They project axons to the spinal cord through the dorsolateral tract of Lissauer {lateral root entry :one} to second-order neurons.
D. Second-order neurons are found in the dorsal horn, They gi\'e rise. to axo115 that decussate in the \'entral white commissure and ascend in the com:ralareral lateral funiculus. Their axons terminate in rhe VPS nucleus of the thplamus.
E. Third-order neurons are found in the VPL nucleus of the thalamus. They project through the posterior limb of the internal capsule to the primary somatosensory cortex (Brodmann's areas 3, I, and 2).
F. Transection of the lateral spinothalamic tra'et results in contralaceralloss of pain and tcmperature belo\\' [he lesion.
IV. LATERAL CORTICOSPINAL TRACT (Figure 7-4; see- also Figure 8-1)
A. Function. The latcml corricospinnl tract meJiatcs voluntary skilled motor 8cti\'it)', primarily of the uprcr limhs. It is not fully myelinarcJ until the end of (he second year (Babinski's sign). . /
B. fiber caliber. Arrroxilll:lccly 90% of the fibers lie between I and 41-1-111, ;Jnd 4% lie .... bo\·e ZO~m (from the giant cells Q( Bctz).
C. Origin and termination
1.. Origin. The brcml corticospinal tract arises (rom layer V of (he ccrcbr;JI cortex (rom three conic;!1 areas in equal aliql1o(s: a. The premotor cortex (nwdm:mn's ;,\r'~;1 (,)
Laleral corticospinal tract (crossed axons of neuron I)
Motor end plates ~eee -r ee
Medulla
Medulla
'-0'-----.1--_____ Pyramidal decussation
of"I:s2::::o-------_ Venlral corticospinal tracl (uncrossed axons of neuron I)
./ Spinal cord
L-':"-'~ _______ Venlral white commissure
Figure 7-4. The Lueral anJ \'L'lllralwrticmpinal (l'yrallliJ;d) tracts. These 1l1;ljnr de~cendillfc: motor p;!th·.\·ay\ mediate \'.,liti.'I1.11 ll1(llor acti\'it\,. TIleccllso(oril;in:lrc located ill rhe prell1(l(or, the !llut():. :n,d the serl-
Figure 7-5. 1l1e oculosympathetic pathway. Hypothalqmic fibers project to the ipsilateral ciliospinal center of the intennediolateral cell column at T-!. The cilfospinal center projects preganglionic sympathetic fibers to
the ~uperior ceIYical ganglion. The ~uperior cer;ical ganglion projects perivascular postganglionic sympathetic fibers through the tympanic c8,\'ity, ca\'emous ~inus, and superior orbital fissure to the dilator muscle of the iris. Interruption of this pathway at any le\"el results in Homer's syndrome. eN = cranial nerve.
• ;.-
c. The primary sensory cortex (Brodmann's areas 3, 1, and 2) . d. Arm, face, and foot areas. The arm and face areas of the motor homuncu
lus arise from the lateral com'exity. The foot area arises from the paracentral lobule.
./ 2. Termination. The lateral corticospinal tract terminates contralaterally, through
intemeurons, on \'en~ral horn motor neurons.
D.' 'Course of the lateral corticospinal tract
1.. Telencephalon. The laterarcorricospinal tract run{in the posterior limb of the internal capsule in the telencephalon.
2. Midbrain. The lateral corticospinal trace runs in the middle three-fifths of the crus cerebri in the midbrain. /
3. Pons. The lateral conicospinal tract runs in the base ef the pons. , 4. Medulla. The lateral corticospinal cract runs in the medullary pyramids. Between
85% and 90% of the cOrticospin:-.1 fibers decussate in (he pyramidal decussation as (he lateral corticospinal tract. The remllining 10% to 15% of the fibers continue as the anrerior corticospinat (rllcr. .
5. Spinal cord. The bteral conico~l'inal trilct runs in the Jorsill quadranr of the latCrill funiculus.
-- ---
44 . Chapter 7 I ...................... ~.: ... ;:~~=~.;;:::~.;~;: .. ;:;~:~::;;.;::;~;.~~.;-;;::;.-........ -.................................................................. I :1. Above the motor decus~iltion, transccti~m results in cOnt;abtc~(l1 spastic parC!'is
and ~al'inskj'~ ~igl\ (upgoing toe).
I 2. In the spinal cord, cmn!>cction _n:~lIlts in .ipsilnceral ~pl\stic p~res_is and Babinski's :oign. -
V. HYPOTHALAMOSPJNAL TRACT (Figure 7-5) I A. Anatomic location. The hYJ)othahullospinal tract projects without int.;!rruption (rom I
the hypothalamus to the ciliospinaI center of the intermediolateral cell column nc T-1 to T- 2. It i~ found in the sJ)inal cord m T-l or abo\'e in_ the dorsolateral quadmnt of the bten-d funiculus. It is also found in the lateral tegmentum_of the. medulla, pons, and midbmin.
B. Clinical features. ImerruJ)-tion of chis tract at any"le\'el results hi Homer's syndrome (Le .. miosis. ptosis. hemianhidrosis, and apparent enophthalmos). The signs are always iJ:'silareral.
I I I I I I I I I I I I I I
I I I I I I
- - --------- ---~ .. -
'·.;/.:~>.i;:i_'
. ~
8 Lesion~ of th'e Spinal Cord
I. .DISEASES OF THE MOTOR NEURONs AND CORTICOSPINAL TRACTS (Fie>-lIr~$ ~-l an~i ~-.:) -' . - -~
A. l..;rrer nl,-"'tor n.euron (UMN) lesions are caused by trllnsecrion of the corticospinal lr.1..::r \.'r \"~c-~tnlction of the cordcnl cells of origin. They result in spastic paresis with fvr:\lni ... bl ~i~l1$ (Babinski's sign). .
B. Lower nwtor neuron (LMN) lesions are caused by damage to the motor neurons. They re.:'lIlr in flaccid paralysis, areflexia,- atrophy, fascicularions, and fibrillmions. Poliomyelitis or \\lerdnig-Hoffman disease (see Figure 8-2A) results from damage to [he 111\.. ... ror neurons.
Gracile fasciculus
jlPsilaterallOSS of taco tile discrimination and '
position and vibration sensation from leg
I Ipsilateral loss of tactile discrimination and
Cuneate fasciculus
position and vibration sensation from arm
Lateral corticospinal tract ;..
Lateral spinothalamic tract
Ventral white commissure
./
Ipsilateral spastic paresis with pyramidal signs
Contralateral/oss of pain and temperature sensation one segment below lesion
/psilateral flaccid paralysis in aNected myotomes
Bilateral loss of pain and temperature sensation within dermatomes of involved segments
Figure 8-:1. Transverse section of rhe ct:r\"icnl spinal cOld. The clinically imporl:llH ascending and descend. ing rathways arc shown on the left. Clinical Jdicits that H';o;l!lt from the intcrrupti(\n of these p;nhways are shown on -thc ri.c:ht. Destructive lesions of the dorsal horns rc~uh ill anc:slhe~ia nIH) mc:l1cxia. Destructioll of the veneral whitc commissure interrupts the ccntrnl trallsllli~si(Jn of !,ain nnd tcmpt:f;1[trrc impuhcs bilatcrally through the later:.! !'Irinothainll1ic tracts.
45
. ~ '; .:.. .
>., .. <
'~:~:' 'A:·i·;> a 'mr uW?ec"lWZM=_Gill' I ..
~.
46 Chapter S
.................................................................................................................................................................................................. I I I I I I I I I I I I I I
C. Combined UMN and LMN diseasc. An cX;Hllplc or a combined UMN nnd LMN dis. e;)sc is nmyotrophic bteraf sclerosis (ALS, or Lou Gehrig':> disC;1SC) (see Figure 8. 21)1. ALS is caused by Jamage to (he COr(iCl)Spinal ([;1((5, with pyr;Hnichl signs, and hy d;I1l':1~c to the LMNs, with Uvil'-J \ynl)'[\)I1)S. P;1i;,~n[:-; wit!\ /\1;'; h;I\'~' ';1) .\('Il'~';\
II. SENSORY PATHWAY LESIONS. An cxmnple of a condirion caused by these lesions is dorsal column disease (tabes dorsalis) {see Figure-B-2CJ.This disease is seen in patients with neurosyphilis, Ie is ch;uncreri:edby n loss of £nctile discriminmion and position and \"(brnrion sen~uh.'n. lrritnth'e im'oh'ement of the dorsal rootS results in pain and paresthesia:,. Patients hn\'e a Rom~rg sign. (Subject srnnds wirh his feet together. When he closes l~is eyes, he loses his bnlanc~. This is a sign of dorsnl column ataxia.)
. .
III. COMBINED MOTOR AND SENSORY LESIONS . .." A. Spinal cord hemisection (Brown-Sequard syndrome) [see Figure 8-2E] is caused by
damage t~) the following structures:
~. The dorsal columns [gracile (leg) and cuneate (arm) fasciculi]. Damage results in ipsilareralloss of ractile discrimination and position and vibration sensation,
2. Tl]e lateral corticospinal tract. Damage results in ipsilateral spastiC paresis with Fytamidal signs below the ·lesion.. .'
3. The lateral spinothalamic tract. Damage results in contralateral loss of pain and temperature sensation one segment below the lesion,
4. The hypothalamospinal tract at T-l and above. Damage results in ipsilateral , Homer's syndrome {i.e., miosis, ptosis, hemi~mhidrosis, and aFparent enoph
thalmos}.
5. Tl1e ventral (anterior) horn. Damage results in ipsilateral flaccid paralysis of in-neryated muscles. .
B. Ventral spinal artery occlusion (see Figure 8-2F) causes infarction of the anterior twothirds of the spinal cord, but spares the dorsal columns and horns. I t results in damage to the following structures:
1.. The lateral corticospinal tracts. Damage results in bilateral spastic paresis with pyramidal signs belo\\' the lesion.
2. The lateral spinothalamic tracts. Damage results in bilateral loss of pain.ansi tem-perature sensation below the lesion. <
3. The hypothalamospinal tract at T-2 and above. Damage results in bilateral Homer's syndrome.
4. The ventral (anterior) horn!:' Damage results in bilateral flacCid paralysis of the innervated muscles.
5. The corticospinal tracts to the sacral parasympathetic centers at S-2 to S-4. Damage .r.esults in bilateral damage and loss of voluntary bladder and bowel control..
C. Subacute combined degeneration {vitamin B12 neurop~thy} [see Figure 8-20] is caused by pernicious {megaloblastic} anemin. It results from damage to the following structures: ./ :t. The dorsal columns (gracile and cuneat~ fasciculi). Damage results in bilateral
loss of tactile discrimination and position and vibration sensation.
2. The lateral cortico~pinal tracts.' Damnge results in bibteral spastic paresis with pyramidnl signs',
3. The spinocerebellar tracts, Dnmage results in bilateral arm and leg dystaxia.
D. Syringomyelia (sec Figure 8-2H) is a central cavitation of the cervical cord of unknown etiology, 1 t results in damage to the following structures:
:1.. The vc!n'tr"l white ccmtmissure. Damage to Jecussating lateral spinothalamk a~ I ... :wis" cml::~$ l'ilarcral 10$s o( {':lin and remperarure sensntion.
2. The "c!ntral horns. UvtN lesions r~$lIlt in flaccid paralysis of the intrin::ic tllll::dt I of rhe h;md::. '
E. Fric!drdch's <lhlXia has th~ same spina"} cord'pnthology and symp"toms ps SUb;lcut~ CO\1"
bined degelleratk1n. . "." , ..
F. Multiple sdc"rosis (see Figure 8-28). Pbques primarily involve the white mmter (If th I
tV.
cerdcal segments of the spinal cord. The lesions nre random and asymmetric"
PERIPHERAL NERVOUS SYSTEM (PNS) LESIONS. An example of a PNS lcsio. is Guillain-Barre syndrome (acute idiopathic polyneuritis. or postinfectious polyneuritis: It rrimarily affects '(he motor fibers "of the "enrral roots and peripheral ner\·es. Clnd it pre duces LMN symptoms (Le., muscle. weakne~s. ascending flaccid paralysis. and areflexia" Guillain-Barre" syndwille has the following features: "
A. It is characteri:ed by demyelination and edema.
B. U~'pcr cen'ical root (C4) il1\"oh'emenr and respiratory paralysis are common"
C. "Caudal cranial i'cn'e ltwoh-emenr with facial" diplegia is present in 50% of cases" " . "
D. Elevated protein le"els may caus~ papilledema.
E. F.
To a lesser degree, sensory fibers' ~re affected. resulting in paresthesias"
The protein le\"el in the cerebrospinal fluid is elevated. but without pleocytosis (albu minocytologic dissociation).
V. INTERVERTEBRAL DISK HERNIATION is seen at the L-4 to L-S or L-5 to S-l inter space in 90% of cases. It appears at the C-5 to C-6 or"~-6 ro C,7 inrerspace in 10% of case~
A. Inten"errebral disk herniation consists of profapse, or herniation, of the nucleus pul posus through the defective anulus fibrosus and into the vertebral canal.
B. The nucleus pulposus impinges on the spinal roots, re'sulting in sp1hal root symptom (i.e., paresrhesias. pain. sensory loss, hyporeflexia, and muscle weakness).
VI. CAUDA EQUINA SYNDROME (SPINAL ROOTS L3 TO CO) results usually fron a nerve roor rumor, an ependymoma, a dermoid tumor, or from a lipoma of the rennin;:; cord. Is characreri:ed by:
A. Severe radicular unilateral pain
B. Sen.sory distribution in unilateral saddle,shapcd area
C. Unilateral muscle atrophy and absent quadriceps (U) <lnd :mkle jerks (S1)
D. Incontinence and sexual functions are not marked
E. Onset gradual and unila~eral /
VII. CONUS MEDULLARIS SYNDROME (CORD SEGMENTS 53-CO) usually result (rom an intramedullary tumor, e.g .. ependymoma. Is characrerized by:
A. Pain usually hilateral and not severe
B. Sensory distrihution in bilatcwl !'addlc-sh:lpcd arca
C. Muscle changes not marked; qU;1driccps and ankle rcflt':'\c$ l1urmal
D. Incontinence ;I!"\d SL':\u:d (unctions SC\Trly iml,;-!ii'n~
I., OVERVIEW. The br,~in stem include~'the medulla, pons, and midbrain. Ir e~tcnd5 from the. pyramidal dec.us:mtion.to the posterior-cotnll1is5ure. The brain stem receh'es its blo<?d supply from the \'crtehobasilar system. Ir contains cranial nerves (CN) III to XII (except the spinal parr I."lf CN Xl). Figures 9#1 and 9-2 sho\\' its surface anatomy.
II. CRO~S-SECTIONTHROUGH THE MEDULLA '(Eig~re 9-3)
A. Medial·structuJ;es
1.. The hypoglossal nucleus of eN XII
2. The medial lemniscus, which contains crossed fibers from the gracile and cuneate nuclei
Rgure 9-:1. The d(lrs,,1 ~ur(ace (l the hrain Mem, The three cerehellar peduncles ha\'e heen remo\'ed to cxr("l!-l: the rh(llllhoiJ fll.\~iI, The trochlear nl:(\'C is the UIlI}· IlCr\'C to exit thc hrain :;rcm from the dors;!1 surfacc. TIll: facial C(,lIiclIllls ~lInn()llnts the gelill (II (ile ;Olclai nt'f\'C anJ the nhllucclH nllcll:lI~. eN = craninl ncrve,
I I I I I I I I I I I I I I I FIgure 9·3. Trnn.w<:rsc .~ccti()n of the medulla at the rnidllli\'<lrv le\'el. The vagal nerve [cranial nerve (eN)
XL hypoglo!'>sal ner\'c (eN XIl), anJ \'c~tibular ner\'e (eN VIII) arc prominent in this section. Thc nuclells am- I higuus g;\'cs ri.\c to special \'bccral <:«(<:r<:nr tillers to eN IX. X, and XI.
I
I I I I I I I I I I I
", .. ;. .; ~""'.
~""~"-!f":~
. ,~,;~~1i?-' :'.
Brain Stem, 51 '. , .......................................................................................................................................................................................................................................... B. Lateral structures
1.. The nucleus amhiguus (eN IX, x, a~'J XI) , ,
2. The vestibular nuclei (eN VIII) . ,
3. The inferior cerebellar peduncle, which contains the dorsal spinocerebellar. cu~ 'neocerebellar. and ,l1li\'ocerebellar trnc(s
4. The lateral spinothalamic tract {spinal lemniscus) .'. ..
5. The spinal trigeminal nucleus and tract of eN v
III. CROSS-SECTION THROUGH THE PONS (Figure 9-4), The pons has a d(lrsal tegmentum and a ventral base.
A. Medial structures
1.. Mediall0l.1gi[udinal fasciculus,
2. ,Abducent nude us of CN V[ (underlies facial collic~lus)
3. Genu (internal) of CN VII (underlies facial nerve) [facial colliculus]
4. Abducent fibers of CN VI
,5. Mediallemni5cus
6. Corticospinal tract (in the bas~ of the pons)
B. Lateral structures
1.. Facial nucleus (CN VII)
. 2. Facial (intraa,=ial) nerye fibers
3. Spinal trigeminal nucleus and tract (CN Y)- ,
4. Lateral spinothalamic tract (spinal lemniscus}
5. Vestibular nuclei of CN VIII
6. Cochlear nuclei of CN VIII
Abducent nucleus (eN VI)
Vestibular nerve (eN VIII)
Facial nucleus (of eN VII)
./
Fourth ventricle
Trapezoid body
".
Middle cerebellar peduncle
Figure 9-4. Transvcrse ~c:ctj()n of the pons;J( the Icvcl of the "hdllcent Illlcll'lIS of cranial nerve (eN) VI and the f<Jcin\ nllc\cu.~ of eN VII. MLF = rnedia\\ongitudiIlOlI fa~ciculus,
Figure 9-5. Trans\'erse section of the midbrain at the level of the superior colliculus. oculomotor nucleus cranial nerve (eN) III, and red nucleus. MLF = medial longitudinal fasciculus.
IV. CROSS-SECTION THROUGH THE ROSTRAL MIDBRAIN (Figure 9,5). The mil brain has a dorsal tectum, an intermediate tegmentum, and a base. The aqueduct lies b tween the tectum and the tegmentum.
A. Dorsal structures include the superior colliculi. B. Tegmentum
:1. Oculomotor nucleus (eN III) • 2. ~ fediallongitudinal fasciculus
3. Red nucleus
4. Substantia nigra ,:
5. Dentatochalamic tract (crossed)
6. ;\·fedial lemniscus .'
7. Lateral spinothal~mic tract (in the spinal lemniscus)
C. Crus cerebo (basis pedunculi cerebri. or cerebral peduncle). The corticospinal trae lies in the middle three-fifths of the crus cerebri.
,. .. V. CORTICOBUlBAR FIBERS (see also Figure 13-4) project bilaterally to al( motor crC.
nial nerve nuclei except the facial nucleus. The division of the facial nerve nucleus th8 innervates the upper (ace (the orbicularis oculi muscle and above) receives bilateral COr ticobulbar input. The division pf the facial nerve nucleus that innervares the lower be receives only contralateral corticobulbar input.
I I I I I I I I t I I I I I I I I I I
I I I I I I I I I I I I I I I I I
'.' -. ... - .
. :- -." ;.. ~ ... . . -:.- .
1.0
. ., -..... .
. Trige'minal System
,,'
.. , ~ . ,; ~ .. ,:,)~.~~~:;~: .: .....
.'
J. OVERVIEW. The trigeminal sysrem'pro\'ides se~sory innervation to the face, oral cavity, and supratentorial dura throu'gh general somatic afferent (GSA) fibers. It alsb innervates tpe muscles of mastication through special visceral efferent (SVE) fibers.
II. THE TRIGEMINAL GANGLION (semilunar or gasserian) contains pseudounipolar gan, glion cells. It has three dh'isions:
A. The ophthalmic nen'e [cranial nerve (eN) V-I] lies in the wall of the C3\'emous si, nus. It enters the orbit through the'superior orbital fissure and innervates the forehead, dorsum of the nose, upper eyelid, oiuit (cornea and conjunctiva), and cranial dura. The ophthalmic nerve mediates the afferent limb of the corneal reflex.
B. The maxillary nerve (eN V-2) lies in the wall of the cavernous sinus and innervates the upper lip and cheek, lower eyelid, 'anterior portion of the temple, oral mucosa of the upper mouth, nose, pharynx, gums, teeth a~d palate of the upper jaw, and cranial dura. It exits the skull through the foramen roturidum.
C. The mandibular nerve (eN V-3) exits the skull through the foramen ovale. Its sensory (GSA) component innervates the lower lip and ,chin, posterior portion of the temple, external.audicbry meatus, and t):mpanic membrane, extern,il ear, teeth of the lower jaw, oral mucosa of the cheeks and floor of the mouth, anterior two,thirds of the tongue, temporomandibular joint, and cranial dura.
D. The motor (SVE) component of CN V accompanies the mandibular nerve (CN Y,3) through the foramen oval~. Ie innervates the muscles of mastication, mylohyoid, anterior belly of the digastric, and tensores tympani and veli palatini. It innervates the muscles that move the jaw, the lateral and medial pterygoids (Figure 10,1).
III: TRIGEMINOTHALAMIC PATHWAYS (Figure 10.2),.'
A. The ventral trigeminothalamic tract mediates pain and temperature sensation from the face and oral cavity.
:1.. First-order neurons are located in the t~ig'eminal (gasserian) ganglion. They give rise to axons that descend in the spinal trigeminal tract and synapse with second, order neurons in the spinal trig~minal nucleus.
2. Second-order neurons are located in the spinal trigeminal nuclells. They gi\'e rise to decussating axons that terminate in the contralateral \'enrral posteromedial (VPM) nucleus of [he thalamus. . .
3. Third-order neurons are 10CIl{cd in the VPM nuclells of the thal;n.nus. They pro'
Figure 1.0-1.. Function .and innervation of [he la.teral pterygoid muscles (lPMs). The lPM receives its in- i nervation from the motor nucleus of the trigeminal nef\'(~ found in the rostral pons. Bilateral innervation of the lPMs results in protrusion of the tip of the mandible in the midline. The LPMs also open rhe jaw. Denervarion of one lPM results in deviation of the manaible to the ipsilateral or weak side. The trigeminal motor nucleus I receives bilateral corticobulbar input. eN = crani<ll nerve; lMN == lower motor neuron; UMN = upper motor neurOn.
jecr through the posterior limb of the internal capsule to the face area of the somatosensory correx. (Broqmann's areas 3 •. 1. and 2).
B. The dorsal trigeminothalamic tract mediates tactile discrimination and pressure sensation from the f~ce and oral cavity. ~r receives input from Meissner's and Pacini's corpuscles.
:1.. First-order neurons lire loented in the trigeminal (g~sserbn) ganglion. They synapse in [he principal sensory nuclells of eN v.
2. Second-order neurons are locHce! in the princip:11 sensory tlt;c1c:::-; or eN v They proj,·u rn the ipsihtCL11 \li't\! :;l:(·lcII'; o( rill. [h:1I;:! '
*The cell bodies are found in the mesencephalic nucleus of eN V. CN = cranial nerve.
I Efferent Limb I
Facial nerve (eN VII) Mandibular nerve (eN V-3)" Facial nerve (eN VII) 'I Vagal nerve (CN X) ,
~ . . . I - 2. The jaw jerk refle.x is a monosynaptic myotatic reflex (Figure 10·3) .
. 3. The tearing (lacrimal) reflex.' "
4. The oculocardiac reflex occurs when pressure on the globe results in bradycardia. I B. Clinical correlation. Trigeminal neuralgia {tic douloureux} is characterized by recur~
rent paroxysms of sharp. stabHng pain in one or more branches of the trigeminal nerve I on o~~. side of the face. It usually occurs in peo"pl.e o,lder than 50, years of age, and it is more common in women than in men. Carbamazepine is the drug of choice for idio~ pathic trigeminal neuralgia. . I
Mesencephalic nucleus with primary neuron
V-3
~~/====::::--~t-~::~' Muscle spindle from masseter muscle
I t
I I
Motor nucleus eN v with secondary neuron
Masseter muscle
'------ Molar division eN v
Principal sel'}sory nucleus of eN v
Spinal trigeminal nucleus
./
Figure :1.0-3. Thc jaw jerk (massc(er) reflex.TIlc a((('rem limb is V-3, and the c(ferent limb is the mOWr root (h;lt ;lCCOl1lpan il's V- 3. Fi rst-ordcr sensory neurons :lrc locHed in the I11csencephal ic noc ICllS, The ja w jcrk reflcx, like 0111 mllscle ~t(t'(ch r<:flcx<:.,, is a mOllmY!1J[1tic rnyo(:l(tic reflex. lIH'crrcfle:xi:1 indiclccs ;1:1 Ill'per 1ll()tCJr nell
Figure :1.0-4. The coritents of the cavernous sinus. ll1e wall of the caverrl'OUs sinus contains the ophthalmic cranial ner,e (eN) V~l and maxillary (CN V~2) divisions of the trigeminal nerve (CN V) and the trochlear (eN IV) and oculomotor (eN III) neryes. The siphon of the internal carotid artery and the abducent nerve (eN VI), al(lng with postganglionic symrachetic fibers, lies within the ca\"eroous sinus.
V. THE CAVERNOUS SINUS (Figure 1O-4) contains the follo\ving structures:
A. Internal carotid artery (siphon)
B. eN III, IV, V,l, V,2, and VI
c. Postganglionic sympathetic fibers en route to the orbit
I ~ OVERVI EW. The auditory system "is. at"} exteroceptive special somatic afferent syste~ tha can detect sound frequencies from 20 Hz to 20,000 Hz. It is derived from the otic vesicle which is a derh'ative of the otic placode, a thickening of the surface ectoderm.
II. THE AUDITORY PATHWAY (Figure 11#1) consists of the following structures.
A. The hair cells of the organ of Corti are innerVated. by the peripheral processes of bipo" lar cells of the spiral ganglion. They are stimulated by vibrations of the basilar membrane
1. Inner hair cells are the chief sensory elements; they synapse with dendrites Oi
myelinated neurons whose a"ICons comprise 90% of the cochlear nerye.
2. Outer hair cells synapse with dendrites of unmyelinated neurons whose a.-xom " comprise 10% of the cochlear nen'e. The OHCs reduce the threshold of the IHCs.
B. The bipolar cells of the spiral (cochlear) ganglion project peripherally to the hair cells of the organ of Corti. They project centrally as ~ c9Chlear nerve to the cochlear nuclei.
C. The cochlear nerve [cranial nerve (CN) VllI] extends from the spiral ganglion [Q
the cerebellopontine angle, where it enters the brain stem.
D. The" cochlear nuclei receive input from the cochlear nerve. They pi-oject contralater~ ally to the superior olivary nucleus and lateral lemniscus.
E. The superior olivary nucleus, which plays a role in sound localization, receives input from the cochlear nuclei. Ie projects co the laeerallemniscus.
F. The trapezoid body is located fn ehe pons. Ie contains decussating fibers from the ven# tral cochlear nuclei.
G. The lateral lemniscus ~eceives input from the contralateral cochlear nucl~i and supe~ rior olivary nuclei.
H. The nucleus of inferior colliculus receives input from the lateral lemniscus. Ie pro~ jects through the brachium of the inferior colliculus CO the medial geniculate pody. "
I. The medial geniculate body receives input from the nucleus of inferior colliculus. Ie projects through the internal capsule as the ~udicory radiation to the primary auditory cortex, the rransvcrse tcmporal gyri of Hcsch!.
J. The transverse temporal gyri of lieschl contain the primary auditory cortex (Brod~ mann's areas 41 and 42). The gyri:'lre locmed in the depths of the lateral sulcus.
III. HEARING DEFECTS
A. Conduction deafness is cnused by interruption of the PZlSS;t(:,C of sound w~vcs chrou!;h t}le external or rniddlc c~r. It In~'y be c8uscd hy of~~tr~H.~:~\.r~ (~~.; .. t \\!;l··~ '. ,d·.·i~,\J~.:!-(! ,).~) "r otitis r1lr:dia. "
Auditory radiations ;n subfenticu/ar part of internal capsule
'------ Medial geniculate body
r---i-------- Commissure of inferior colliculus
Nucleus of inferior cotliculus
crD-------Laterallemniscus
}--.----- Nucleus and commissure of lateral lemniscus
Spiral gangli;~ Cochlear nerve (CN VIII)
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,,'.
Figure 1.1.-1.. Peripheral and central connections of the auditory system. This system arises from the hair cells of the organ of Corti and terminates in the transverse temporal gyri of Heschl of the superior temporal gyrus. It is characterized by the bilaterality of projections and the tonoropic localization of pitch at all levels. For example, high pitch (20,000 Hz) is locillized at the base of the cochlea and in the P9sterol!ledial part of the trans\·erse temporal gyri. eN = cranial nerve. .
B. Nerve deafness (sensorineural, or perceptive,. ·deafness) is caused by disease of the cochlea, cochl~<lr nerve (acoustic neuroma), or central audiwry connections. It is usually caused by presbycusis that results from degenerative disease of the organ of Coni in the first few milJimecers of the basal coil of the cochlea (high-frequency loss of 4000-8000 H:).
IV. AUDITORY TESTS. A. Tuning fork tests (T.1ble II~I)
Nerve deafness (left ear) Nerve deafness (right,ear) Normal ears
Table 11-1. Tuning Fork Test Results
Web~rTest _
Lateralizes to left ear
Later.atizes to right ear
Lateralizes to right ear Lateralizes to left ear No laterlization
Rinne Test
, BC > AC on left AC :>' BC on right BC > AC on right AC > Be on left AC > BC, both ears AC > BC, both ears AC > BC, both ears
" Condl,lction deafness = middle ear deafness (e.g .• otosclerosis. otitis media); (lerve deafness = sensorineural deafness (e.g .• presbycusis; AC = air conduction: Be = bone conduction.
1.. \Veber's test is performed by placing a dbrating tuning fork on the \'ertex of the skull. Normally, a patient hears equally on both sides. a. A padent who has unilateral conduction deafness hears the vibration more
loudly in the affected ear., . . . b. A patient who has unilateral partial nerve deafness hears the vibration more
loudly in the normal ear. "
2. The Rinne test compares air and bone conduction. Ie is Ferformed by placing a vi, brating tuning fork on the mastoid process until the vibration is no longer heard; then the fork is held in fronc of the ear~ Normally, a paciene hears the vibration in the air after bone conduction is gone. a. A patient who has unilateral conduction deafness does not hear the 'libra'
tion in the air after bone conduction is gone. b. A patient who has unilateral partial nerve deafness hears the vibration in che
air after bone conduction is gone.
B. Brain stem auditory evoked potentials (BAEPs) ',"
:1. Testing method. Clicks are presented [0 one'ear, then (0 the o;:her. Scalp elec, trodes and a compurer generate a series of seven waves. The waves are associated with specific areas of the auqitory pathway.
2. Diagnostic value;. This method is valuable for diagnosing brain stem lesions (mul, tiple sclerosis) and posterior fossa tumors (acoustic neuromas). It is also useful for assessing hearing in infants. Approximately 50% of patients with multiple sclerosis have abnormal BA.EPs.
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1.2 Vestibular System
I. OVERVIEW. Like th~ audit~ry systeql. the \'estibuhlr system is derh'ea fro;n'the otic vesi, cleo The otic vesicle is a deri\'mi\'e of the·otic placode, which is a thickening of the sur, face ect~derm. This system maintains posture and equilibrium and coordinates'head and eye movements.
II. THE LABYRINTH
A. Kinetic labyrinth
i. Three semicircular ducts lie \\'ithin the three semicircular canals (Le., superior, lateral, and posterior).
2. These ducts respond to angular acceleration and deceleration of the head. a. They com.ain hair cells in the crista ampullaris. The hair cells respond to en,
dolymph flow.
Vestibular nuclei .......
Inferior cerebellar peduncle -.-
MLF,
Inferior olivary nucleus- .-
'\ '\
Medial lemniscus /
/ Nodulus /
'\
'\ Pyramid
Semicircular ducts t 1\'
Flocculus / .
- - -Juxtarestiform body
\ /
I \ I \ I \
'v
1 \ I \ I
\ / .,'
~ - Ves~ular nerve and ganglion in internal auditory meatus
,Ampulla .. / / and crista
. /. Utricle . " ,,/ and macula
\
Endolymphatic I duct
Cochlear duct
Saccule and macula
Figure 1.2-1.. Peripheral connecrions llf the \'cstihJlar system. The hair cells of rhe cristae ampullares and the lIl:lculae of the utricle and saccule l'Tl'ject, through the vestihular nerve, to the \'esribul;u nuclei of the medulla and pons and the flocculonodubr lobe of the cl'rcbcllum (vcstibuloccrchcllulIl). l\tLF = mcdiallongiti.iJinal fasciculus.
b. End()l~:mph flow roward the ampulla (nmpulll'lpcral) or utricle (utricu!t,peral) ,is n ~rr(lnger ~timulus tll.\n is endolymph flow in the opposite direction.
B. Static labyrinth
i. Thl! utri~le nnd saccule re~rond to the positiono( the I~end with respect: to linear acce1ernti.on an.d rhe pull of gravity.' .
2. Thl!utr:icle nnd. sncclile contain hair cells whose cilia are embedded i~ .the otoiithic membrane. When hair cells are bent toword the longest cilium (kinocilium), the frequency of sen~ory discharge increases.
III. THE VESTIBULAR PATHWAYS (Figures 12-1 and 12,2) consist of the follow'ing s(ruc, (ures,
I I 1 I I
A. Ha"ir c~l1s of the semicirCular ducts, sa~ule, a~d utricle are i';nerva,ed by periph. "I eml rrocesse$ of bipolar cells of t.he \'estibular ganglion.
Vestibular area of cerebral cortex ___ ~~~
v sntral posterior inferior nucleus ----"l!s;:=::7.~'t_-~
Vestibulothalamic tracts
Midbrain --______ ~_
Abducent nucleus cf CN VI of pons
Vestibular nuclei
MlF--r-q.>/
---j'--~:t-:-r~Tt-- Thalamus
-{---+---- Oculomotor nucleus of CN II I --,--t----Trochlear nucleus Qf CN IV
----t"---;--;;n- Nodulus of cerebellum
-:--------- Vestibular ganglion
r-.-- Cochlea
Clh;--- lateral vestibulospinal (Deiters') tract
Figu re 12-2. The major cClHr:l1 connections o( the vestibular system. Vestibular nuclei project, through the ascending rncdinllongitudinal (;l.~ciclJli (MLF), to the ocular motor nuclei anJ sllb~cf\'e vcstibllJu-ocubr rc!1cxcs. Ve:< ( j hu /;1 r (Hie Ie j ;dso rroj cc t. through the dcscc ndi ng I\ff.F ;1 nd !:teer;1! \'CS( i hl tin.,!, ill;,) U;IC[S, to [h c v (' n [nl h () rI1
~. The vestibular ganglion is locnccJ in the fundus of r1~e internal i1uJitory meacus.
':1.. Bipolar neUf(Il\$ prl\jeC[ through their periphernl processes to the hnir cells.
2: Bipolar neurolH prl1ject their cemr,,} processes <1S [he vestibular ner\"(~ [cr.lnial nerve (eN) Vlll) .t'-, {he \'estibubr nu.c!ei and to the flocculonodubr k'be of the cerebellum. . . '
C. Vestibular nuclei
.:1.. These nudei receh'e input from: . a. The semicircular ducts, saccule, and utricle b. The flocculonodubr lobe of [he cerebellum ..
2. The nuclei project fibers to: a. The t1occulonodular lobe o'f [he cerebellum· b., eN III, IV. and VI through [he mediallongirudinalfasciculLls (MLF) c. The spinal cord through the lateral \'estibulospinal truCt d. The \"entr.,l rO$teroinferior and 'posterolateral ,nuclei of the thalamu$, both of'
which project t(' the postcentral gyrus
IV. VESTIBULO·OCULAR REFLEXES are mediated by the \'estibular nuclei, ~1LF. ocular moror nuclei, and eN III, I\: and VI.
A. Vestibular (horizontal) nystagmus
:1.. The fast phase of nystagmus is in the direction of rotation.
2. The slow phase of nystagmus is in the opposite direction.
8. Postrotatory (horizontal) nystagmus
:1. The fast phase of nystagmus is in the opposi~e direction of rotation.
2. The slow phase of nystagmus is in the direction of rotation.
3. The patient rast,points and falls in the direction of pre\-ious rotation.
C. Caloric nystagmus (stimulation of horizontal ducts) in normal sul;>Jects
:1. Cold water irrigation 'of the external audito.,: meacus results in nystagmus to the opposite side.
2. \Varm water irrigation of the external auditory meacus results in nystagmus to the same side. ./
Figure 12·3. Cold caloric resron~cs in thc lJI1Wn~ci\lllS I';lticnt. \'Vhcn the hmin stcm is intact, the cyes dc\"i:ltc [(lw:lrd thc irrigated side; with hilateral triln~c('ri\1I1 \If rhl' IIlcdbllnngiC\l\linal f:1sciculi (MLF), thc eye de, vi,He;'; to thc ahJucteJ siJc. Dc!>truction ()f thc cauJall>rain :;t(,111 rcsulcs in no d~'\'ia[ion of the eyes, DOllb/.c-headcd (ITTfJW$ indicatc nystagmus; ,~iTlJ!lc-hcaded arTfJWS indica!\.' dc\"brillll of (hc eyes [\1 (Inc side.
. ., .... ';' ':"':~C . , '1 ... -. ..,. .. 'd
l 64. Chapter 12
................................................................................................................. : ............................................. , ..................................... . 3. Reme,mber the mnemonic.CO\YS: Ccrld Opposite, \Ynnn Same ..
D. Test re::ults in unconscious subjects (Figure 12-3)
I
:1. N\.) nystngtnus is seen. J 2. \Vhenthe brain stem is in~nc[, there is deviation of the eyes to the side of the C(,){,
irrigation.
I
3. \Vith bilaterallv1LF transection, there is deviation of the abducting eye to the sid, of the cold irrigation. . .
4. \Vith lower brain stem damage to the vestibular nuclei, there is no deviation of thl eye5.
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:13 'Cranial NerveS
. .
_'--T.HE",O...L.EAC.xORY~ERVE, the first cranial nerve (eN 1) [figure 13~1J. mediates 01 't~'\ction (smell). It is the only sensory s}'stem that has no precortical relay in the thalamus The olfactory nerye is a special visceral afferent (SVA) nerve. It consists of unmyelinacec axons of bipolar neurons that are located in 'the nasal mucosa, the olfactory epithelium. 1 ( enters the skull through the cribriform plate of the ethmoid bone (see appendix).
A. Olfactory pathway
1. Olfactory receptor cells are.first.order neurons that project to the mitral cells of the olfactory bulb.
2. Mitral cells are the principal cells of the olfactory bulb. They are excitatory and glutaminergic. They project through the olfactory tract and lateral olfactory stria to the primary olfactory cortex and amygdala.
Olfactory trigone Anterior periorated
substance ----::~
Olfactory bulb (eN I) Optic chasm Olfactory tract
Infundibulum Tuber cinereum
Mamillary body Interpeduncular fossa .......,'"--'~...,..... ~'-:.r--Optic tract
Crus cerebri (cerebral peduncle)'
Pons - ........ -+Ir~~="::: Middle cerebellar
peduncle --~
... CN V (motor root) CN.v (sensory root) CNVr' CNVII . CN VII (intermediate)
Figure :13·:1. The ha~c of [he hrnin wirh aewehed cranial /lcn'cs (eN). (Reprillfl,.1 with permission (rom Tru<::< Re, Kellncr CE: f)cUli/cd Atlas of the Hcaclllnd Neck. New York, Oxford Ulli\'t'r~i{)' Prl'ss, 1958, p. 34.)
B. Lesions of the olfactory pathway result from rrnllln.a (e~g., skull fracture), and, ofter 1 from 'olfactory gro,-we meningiolllCls. These lesions cause ipsilateral anosmia (loc~lli: ing .".due). Lesions th:lt invoke the p:lmhippocampal uncus may cau~e olfactory l~aJ ludnarions'[uncimue fits (sei:ures) wirh deja \·u}. . " 1
c. Foster Kennedy s'y:nl:irome (FKS) consists of ipsilClteral anosmia, ipsilateral optic atro phy, and contralateral papilledema. It is usually cClused by nn anterior fossa meningiomc::
1
J.!!. THE.0.6.uLOMQI.P.ftJj.J§,R~gJ9.NJIJ) is a gen~ral somatic efferent (GSE), general \·is· ceral efferent (GVE) nerye. ,
A. General characteristics. The oculomotor nerve moves the eye, constricts the pupil, accommodates, and con"erges. It exits the brain stem from the interpeduncular fossa of the midbrain, Fasses through the ca\'emous '.Sinus, and enters the orbir through the superior orbital fissure. . -
:1.. The GSE componenrarises from the oculomotor nucleus of the rostral midbrain. I It innervates four extraocular muscles and the levator palpebrae muscle. (Re, member the mnemonic SIN: superior muscles are intorters of ehe globe.) a. The medial rectus muscle adduces the eye. With its opposite partner; it con, ,
\'erges the eyes. b. The superior rectus muscle elevates, intorcs, and adduces the eye. c. The inferior rectus muscle depresses, extorts, and adducts the eye. d. The inferior oblique muscle elevates, e'xtorrs~ and abducts the eye . e. The levator palpebrae muscle elevates the upper eyelid.
2. The GVE component consists of preganglionic parasympathetic. fibers. a. The Edinger~\Vestphal nucleus projects preganglionic parasympathetic fibers
to the ciliary ganglion of the orbit through CN III. . b. The ciliary ganglion projects postganglionic parasympathetic fibers to the
sphincter muscle of the iris (miosis) and the ciliary muscle (accommodation).
B. Clinical correlation
:1. Oculomotor paraly~is (palsy) is seen with rranstentorial herniation (e.g., tumor, subdural or epidural hematoma);·
, I t 1
a. Denervation of the levator palpebrae m,:!scie ,~ause~ ptosis (Le., drooping of the upper eyelid). '
b. Denervation of the extraocular muscles causes the affected eye to look "down and out" as a result o( the unopposed action of the lateral rectus and superior oblique muscles. The superior obliql!e' and bternl rectus muscles are inner' "aced by eN IV and CNVI, rcspccti\;ely. Oculomotor palsy results in diplopia (double vision) when the p:1cienr looks in rhe direction of the pareric muscle.
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c. Interruption of paras),mp:lt!lctic innervation (internal ophthnlmoplegia) re, suits in a dilated, fixcd pupil and paralysis of accommodation (cycloplegia).
2. Other conditions associ:ltcd with eN III imp;lirmcnt a. Transtentorial (uncal) herniation. IncreascJ supratentorial pressure (c.g.,
(rom;) [urnor) (orces the hi!1pOclmp:1l11nCtIS through the [cnrori;d !I(l[{:: "'ld (\}In;::·f_'·-~,{'·; or srr('lc!V?:\ the '. :: ,~cr\r'
. Cranial Nerves ,,67 ................................................................................................... ~ ........................................................................................................... . (:1) Pupilloconstrictor fibers nre nffected first. resulting in a dilated, fi'\:ed pupil. (2) Somatic efferent ,fibers are affected later. resulring in externnl,strabis-
, mus (exotropb). ," b. Aneurysms of the c;uotid and posterior communicntiI;g arteries often 'COIl1~
press CN III within rhe cavernous sinus or interpeduncular cistern. They USLl~ ally affect the'periphernt pupilioconstricror fibers first {e.g .• uncal hemiation}.
c. ' Diabetes mellitus (diabetic oculomotor palsy) often affects the oculomotor " nerve. Ie damages the central fibers a11d spares the pupillOconstricto'r fibers.
IV. THg IROCHLEAR..NER.\lE..(-CNJV) is a GSE nen'e. .' , " -A. General characteristics. The trochlear nerve is a pure motor nerve thm innervates th~
5urerior oblique muscle. This 111uscle depresses, intorrs, and abducts the eye. (See Fig~ ur~ 17~4Q.)
. . . . :1. It arises from the contralater?l trochlear nucleus of the caudal midbrain.
2. It aecussates beneath the superior medullary velum,of ti1e midbrain and exits the . brain stem on its dorsal surface, caudal to the inferior colliculus.
3. It encircles the midbrain within the subarachnoid space, passes through the'ca\'~ ernous sinus. and enters the orbit through the superior orbital fissure.
B. ,Clinical, correlation. eN IV paralysis resulcs in ~he' follo\ving conditions:
:1. Extorsion of the eye and weakness of downward gaze
2. Vertical diplopia, which increases when looking down
3. Head tilting to compensate for extorsion (may be misdiagnosed as idiopathic tor~ ticollis) ,
4. Head trauma. Because of its course around the midbrain, the trochlear nen'e is particularly vulnerable to head trauma. The,trochlear decussation underlies the su~ rerior medullary velum. Trauma at this site'often results in bilateral fourth~ner\'e ralsies. Pressure against the free border of the tentorium (herniation) may injure the nerve. '
v. IHETRIGEMINAL NERVE (eN V) is? special visceral efferent (SVE), general somatic , "afferent (GSA) 'i1'er\'e (see Chapt'erTO) ..
A. General characteristics. The trigeminal nen'e is the nen'e of pharyngeal (brachial) arch 1 (mandibular). It has three divisions: ophthalmic (CN V~l), maxillary (CN V~2), and mandibular (CN V,3) [see Chapter 10].
:1. The SVE component arises from the moror trigeminal nucleus that is found in the lmeral midpontine tegmentum. It innervatesch~, mus~les of mastication (i.e., temporalis, masseter, lateral. and medial pterygoids), the [ensores tympani and veli pabtini. the myelohyoid muscle. and the an~erior belly ~f the digastric muscle.
2. The GSA component provides sensory inne;vation to the face, mucous membranes of the nasal and oral cavities and frontaltinus, hard palate. and deep structures of the he:1J (proprioception from muscles and the temporomandibular joint). It inner~ \'iues the dura of the anterior and middle cranial fossae (supratentorial dura). . .
B. Clinical correlation. Lesions result in the following neurologic deficits:
:1. Loss of general sensation (hemianesthesia) from the face and mucous membranes II (he oral and nas:11 cm'itics
2. Lllss of the corneal t' ... [!I.OA ( .. [[I.'II':11l :iIlIU, eN V-}} (Figure 13~21
mag wrm mrS'7m
I .68 Cha.pter 13 ................................................................................................. _ ................................................................................................ ,
Princip~1 sensory nucleus (eN V)
Primary neuron
V·2
--~-V-3
/" , I
I .1
Tertiary neuron ......:o.'\"""""'~ •.
Decussating corneal reflex fiber
Secondary neuron.
Spinal trigeminal nucleus
Spinal trigeminal tract
Trigeminothalamic pain fiber
Figure :1.3-2. The corneal retlex pathway showing the three neurons and decussation. This reflex is consensual. like the pupillary light reflex. Second·order pain neurons are found it:l the caudal division of the spinal trigeminal nucleus. Second-order corneal reflex neurons are found at more rostralle\'els.
• 3. Flaccid paralysis of the muscles of masticati.0r'l.
4. Deviation of the jaw to the weak side as a result of the unopposed action of the opposite lateral pterygoid muscle
5. Paralysis of the tensor tym~ani mu.scle, which leads to hypoac~sis (parcial deaf~ ness to low.pitched sounds)
6. Trige~inal neuralgia (tic douloureux), which is characterized by recurrent paroxysms of sharp, stabbing pain in one or more branches of the nerve (see Chapter 10)
VI. THE ABDUCENT figBVE:(.CN VI) ~ ... , ..... ,-,." ,'""._., .. ,_ ....... -. - ....... .
A. General characteristics. The abducent nerve is a pure GSE nerve that innervates the lateral rectus muscle, which abducts the eye. .' :1. It arises from the abducent nucleus that is found in the dorsomedial tegmentum of
the caudal pons.
2. Exiting intrllaxial fibcrspa.ss through thc c9tticospinal [Tact. A lesion results in al-ternating abducent hemiparc~is. .'
3. It passes through the pontine cistcrn :md cavcrnous sinus and enters the orbit through the superior orbital fissure.
B. Clinical correlation. eN VI paralysi" ~r, ~!~.: .. Iv:.l cominon isolntcd palsy that results from the long peripheral course oCtile nervc.lt is seen in patients with meningitis, subnrachnoid hcmorrh;1gc, brc·stage syphilis, ;1nd rr;\Umn. Abducent nerve p;lralysis re~llitS in the following dcfcct~:
1.. Con\'ergent (medial) ~trahismus (esotropia) 'yithinnbility to "bJlIct the eye
2. Hori:ontal diplopi~ with n\Clximum sep:lrCltion o(the double illl;1ges when k'lok-, ing toward the ~':lretic I:\teml rectus muscle '
~II. T~ E FACIAL N.1;,RVE?~~m,,~=, '. . . . 0
,~ ,1(. Gene~at characteristics. The facialner\"t! is'" GSA, general visceral afferent (GVA), SYA, GVE, and SVE nen'e (Figures 13-3 nnd 13-4). It mediates facial movements, taste, salivation, lac'riniation, 'and general'sensation from the external ear. It is the nerve I?f the rharyngenl (brachia\) arch 2 (hyoid). It includes the fncial ner\'e proper {motor division), which contains the SVE fibers that: innervate the mus~les of facial {mimetic} expression. eN VII includes the intermediate nerve, which contains GSA, 5\ '.-\. and GVE fibers. All first-order sensory neurons me found in the geniculate ganglkm within the temporal bone.
i,. Anatomy. The facial. nerve exits. the. brain st~m in d{e cerejJellcit10nrine angle. It enrers the internal auditory meatus and the facial 'canal. It then exits the facial
. canal and skull through the stylomastoid foramen.
2. The GSA component has cell bodies located in the geniculate ganglion. lr inner\'ates the FoSterior surface of the external.ea: through the posterior auricular branch of eN VII. It projects ,centrally, to the spinal trigeminal tract and nucleus.
3. The GVA component has no dinical significance. The cell bodies are located in the geniculate ganglion. Fibers innervate the soft palate and the adjacent pharyngeal wall.
4. The SVA component (taste) has cell bodies located in the geniculate ganglion. It
CNII Trigeminal ganglion
.,,~
Major petrosal nerve
Nasal and palatine' glands
Superior salivatory nucleus (GVE)
Tongue (taste, anterior two-thirds)
Submandibular gland
Motor nucleus of eN VII (SVE)
Nucleus of solitary tract
Solitary tract (SVA)
.",- Motor root nerve of eN VII in stylomastoid foramen
(e.g., BeU's palsy) ....-... Orbicularis _O_C_UI_i ---~c::_\_-<®» I Buccinator
C'-..r") Orbicularis oris ------'-r--<
Platysma
Figure 13-4. Corcicobulbar innervation of the facial nerve (cranial nerve (eN) VII] nucleus. An upper rnocor neuron (UMN) lesion (e.g., stroke im'olving the internal capsule) results in contralateral weakness of the lower f;1CC, With sparing of the upper face. A lower mororneuron (LMN) lesion (e.g., Bell's pa Isy) result:s in paralYSis of the facial muscles in both the upper and lower face.
p'rojects centrally [0 the solitary tract and nucleus. It innervates the taste buds from the anterior two-thirds of the tongue through: .' a. The intennediate nerve
b. The chorda tympani, which is loc:lted in the tympanic cavity medial to [he tympanic mernb~ane and malleus. It coritains the SVA and GVE (parasympa~ thetk) fibers.' ./
c. The lingual nerve (n branch ofCN V~3) d. The central gustatory path~vay (see Figure 13-3). Taste fibers from CN VII,
CN IX, and CN X project through the soliwry tract to the solitary nucleus. The solitary nucleus' projects through the central tegmental tract to the ventral posteromedial nucleus (VPM) of the thnl:lmus. The VPM projects to the gustatory cortex of the pilrirlallobe (parieral operculum).
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Cranial. Nerves 71. '. .. .. .. . .............................................................................................. _ ....................................................... , .............. : ........................................ . b~rimal. sublll.mdibular, and sublingual glands. I t contains rreganglionic parasympathetic;- neurons "that are I(.lcared in thc superior sa Ii va cory' nuclct,Js of the calldal
" l'l)l\S.
a.' Lacrimal pathway (sec Figure 13-3). The sup~rior salh'atory nucleus pn)jects through the imermeJinre and greater perros.ll nerves rothe pterygopalnrine (sphenopabdne) ganglion. The pt~rygopalmine ganglion projects to the' lacrimal gbnd of the orbit.
b. Submandibular" path\\~ay (see Figure" 13-3). The'surerior salivatory 'nucleus projects through the intermediate nerve and chorda tympani to the ~ub-, mandibular ganglion, The submandibular ganglion projects to and imi.ernues the submandibular and sublingual glm1ds.
6. The SVE component arises from the facial nucleus, loops around the abducent nucleus of the caudal pons, and exits the brain stem in the cerebellopontine angle. Ie enters the internal auditory meatus. tra\'erses the facial'canal, sends a branch 'to. the stapedius muscle of the midd.le ear, and exits the skull through the stylomastoid fommen: It innervates [he muscles offacial expression. the stylohyoid r11uscle,
. the posterior belly of the digastric muscle. and the stapedius muscle.
B. Clinical correlation. Lesions (see Figure 14-2) cause the following conditions:
:1.. Flaccid paralysis of the museles of facial expression (upper and lower face)
2. Loss of the corneal reflex (efferent limb), which may lead to corneal ulceration
3. Loss of taste (ageusia = gustatory anesthesia) from the anterior two-thirds of the tongue, which may result from damage [0 the chorda tympani
4. Hyperacusis (increased acuity to sounds) as a result of stapedius paralysis
5. Bell's palsy (peripheral facial paralysis), which is caused by trauma or infection and im'oh'es the upper and lower face
6. Crocodile tears syndrome (lacrimation d~ring eating), which is a result of aberrant regeneration after trauma
:j • Supranuclear (central) facial palsy, which results in contralateIClI weakness of the . lower face, with sparin'g of the upper face (see Figure 13-4)
8. Bilateral facial nerve palsies, which occur in Guillain-Barre syndrome (see Chapter 14)
9. Mobius' syndrome, which"~onsists of congenital facial diplegia (eN VII) and con\'ergent strabismus;( eN VI)
VIII." THE VESTIBULPCOCHLEAR NERVE (CN VIII) is;m SSA nerve. It has twO tunc-. ti,onaldivisions: the vestibular nerve. which maintains equilibrium and balance, and the
cochlear nen'e, which mediates hearing (see Chapters 11 and )2), It exits the brain stem at the cerebellopontine angle ilnd enters the inter~al auditory meatus. Ie is confined to the temporal bone, ./
A. Vestibular nerve (see Figure 12- 1)
:1.. General characteristics a. It is associated· functionally with the cerebellum (flocculonodular lobe) and
ocular motor nueld. " b. It regulates compensatory eye movements, c. Its first-ordcr sCll$llry biPl,lar neurons me located in the vestibular ganglion in
d.' It projects its ~ripher;)l processes to !he hnir cells of the crisrne of the s~mi,1 drcularducts ;md the hair cells of the utricle nnd,saccule. ,
e~ It projects its central 'processes to the four vestibular nuclei \.)( the brain stt!ll' ,
and the Oocculon ... 1dular lobe of rhe cerebellum. f. Ie conducts effert!nt fibers to the hair cells from the brain stem.
,2. Cliriic;tl correlation. Lesio~sresult in disequilibriu'm; vertigo, and nystagmus.
B. Cochlear nerve (see Figure 11·1) . I :1.. General characteristics ,
a. Its first·order sensory bipolar neurons nre located in the spiral (cochlear) gnn· glion of the modiolus of the cochlea, within the temporal bone.
b. It projects its peripheral processes to die hair cells of the organ 'of Corti. c. Ic projects its central processes to the dorsal and ven'cral cochlear nuClei of tht -I
brain stem.-. d. Ir conducts efferent fibers tp ~he'hair cells from- the brain stem.
2. Clinical correlation. Destructh'e lesions cause hearing loss (sensorineural deaf· ness). Irritatiye lesions can cause tinnitus (ear ringing). An acoustic neuroma (schwannoma) is a Schwann cell tumor.of the cochlear Derye that causes deafness (see Chapter 14).
I
IX~..w:: GLOSSOPHARYNGEAL NE~VE (eN IX) is a GSA, GVA, SVA, SVE, and GvE~erVe'«Figu(ei-3-;5 }:-_----------:- ,-- __ d
A. General characteristics. The glossopharyngeal nerve is primarily a sensory nen·e. Along ,with CN X, CN XI, and CN XII, it mediates taste, salivation, and swallowing. It mediates input from the carotid sinus, which contains baroreceptors that moniwr arterial blood pressure. It also mediates input from the carotid body, which contains chemoreceprors thC\t monitor the CO2 and 02 concentration of the blood.
" .. :1. Anatomy. eN IX is the nerve of pharyngeal '(branchial) arch 3. Ie exits the brain
stem (medulla) from the postolivary sulcus with eN x and CN XI. It exits the skull . through the jugular foramen with CN X and CN XI.. ,,~
2. The GSA component innervates part of the external ear and the external audi· tory meatus through the auricular branch of the vagus nerve. It has cell bodies in the superior ganglion. It projects its central processes co the spinal trigeminal tract: and nucleus. ,,'
3. The GVA component innen'ares structures that are deri\'ed from the endodern1 (e.g., pharynx). It innervates the mucous membranes of the posterior one·third of the to'pg~,e,:tonsil, upper pharynx, tympanic cavity, and auditory tube. It also in~ nervates the carotid sinus (baroreceptors) a~d carotid body (chemoreceptors) through the sinus nerve. It has cell bodies in the inferior (petrosal) ganglion. It is rhe afferent limb of the gag reflex and the carotid sinu's reflex.
4. The SVA component innervates the taste btids of the posterior one,third of the tongue. It has cell bodies'in the inferior (petrosal) ganglion. It projects its central processes to the solitary tract rind nucleus (for a discussion of the central path\vay, see VII A 4 d).
5. The SVE component innervates' only rhe stylopharyngeus muscle. I t arises from [he nucleus ambiguus of [he lateral medulla.
6. The GVEcomponcnt is a pnrasymp;lthctic component tklt inncrv;]tcs the parotid gbnd. Prcg;-mglionic par(lsymp~l!hctic neurons :1rC loclter! in d)t~ infcri\~'r saliv;uory nucleu-; o( rlw I\wdulb, Thc)' pro;l''-' r!':f.l'.:,:l, :1,,',,:"; ;,'\~-'i:- , :,;!, ;,' :-.,~t")~ ,:
Figure :1.3:5. Inneryation of the palatal arches Clnd uvula. Sensory in.nerva~ion is mediated by the glossopharyngeal nerve (cranial ner·::;:-(CN) IXJ. Motor il11~rvatiL)n of the palatal arches and uvula is mediated by the vagus nen'e (CN X). (A) A normal palace and u\'ul~ in a rerson who is saying "Ah." (B) A patient with an upper motor neuron (Ul'v{N) lesion (lefc) and a lower Illotor neuron (LMN) lesion '( light). \V'hcn this patient says "/\h." the pillaral arches sag. The uvula deviates toward the incact{lefc) side .
./
nerves to [he otic ganglion. Postganglionic fibers from the uric ganglion project [0
the parotid gland through the ~uricLJlotemporal nen'e (eN V~3), B. Clinical correlation. Lesions cause the {ollowing conditions:
.:1. .. Loss of the gag (pharrngeal) reflex (interruption of the'afferent limb)
2. Hypersensitive carotid sinus reflex (syncope)
3. Loss of general sensation in the pharynx, tonsils, fauces, nnd back of the tongue
74 Chapter 13 ............................................................................................................................................................................................................... 4. Loss of t~ste 'fr~m the posterior llne.th.ird of the .tongu~
5. Glossopharyngeal neuralgia, which is ch:lr:\cte.ri:eJ by severe stabbing pain in the root eJf th~ t\)i1gUC
x. THE VAGAL N;RVE (eN X) is ~ GSA, GVA, SVA, SYE, and GVE nen'e {see .Fig. ~;j .. $f~"'·: .' .. , A. General charncteristics. The vagal nen'e mediates phonation, swallowing (with CN
IX, eN XI, and eN XII). elevation of the palate, taste, and cutaneous sensation from the ear. It innervates the viscera of the neck, thorax, and abdomen.
:1.. Anatomy. The vagal nen'e is the nerve of pharyngeal (brachial) arches 4 and 6. Pharyngeal arch 5 is either absent or rudimentary.lt exits the brain stem {medulla} from the rostolivary sulcus. Ic-exirs the skull through the jugular foramen with eN IX and eN XI.--·· ···,.-:t'l.,,~· -- .....
2. The GSA ~omponent in~enlates ~he infratentorial dura, external ear, external au· ditory meatus, and tympanic membrane. It has cell bodies in the superior (jugular) ganglion. and it projects its centr:ll processes ro the spinal trigemimil tracr and nu· deus.
3 •. The GVA component inD~r\lates the mucous. m~mbranes of the pharyn.x.; l?-rynx, esophagus. trachea, and thoracic and abdominal viscera (to the left colic flexure). It has cell bodies in the inferiodnodose) ganglion. It projects its central processes to the solitary tract and nucleus.
4. The SVA component innervates the taste buds in the epiglottic region. It has cell bodies in the inferior {nodose} ganglion. It projects its central processes to the soli· tary tract and nucleus. For a discussion of the central pathway, see VII A 4 d.
5. The SVE component innervates the pharyngeal (brachial) arch muscles of the lar~ yn..x and pharynx, the striated muscle of th,~ upper esophagus, the muscle of the U\'ula, and the levator veli palatini and palatoglossus muscles. It receives SVE in· Fut from the cranial division of the spinal accessory nerve (eN Xl). It arises from the nucleus ambiguus in the lateral medulla. The SVE component provides the ef· ferent limb of the gag reflex.
6. The GVE component innervates the 'viscera of the neck and the thoracic (heart) and abdominal cavities as f~r as the left colic flexure. Preganglionic parasympathetic neurons thar are located in the dorsal mowr nucleus of the medulla project to the terminal (intramural) ganglia of the visceral organs (see Figure 18-2 and Table 18-1). .
B. Clinical correlation. Lesions and reflexes cause the following conditions:
:1.. Ipsilateral paralysis of the soft palate, pharynx, and larynx that leads to dysphonia (hoarseness), dyspnea, dysarthria, and dysphagia
2. Loss of the gag {palatal} reflex (efferent li~b) . I
3. Anesthesia of the pharynx and larynx chat leads (0 unilateral loss of the cough reflex .
4. Aortic aneurysms and tumors ~f the neck and thorax rhllt frequently compress (he vagal nerve .
b. L"omplctc laryngeal paralysis, which c;m be r;1pidly (awl i(it is bibtcral (asphyxia)
7. The \.~ulo<:ardiac reflex, in whkh pre~ure on the eye slows t.he heart rate (affel ~nt .limb of CN V-I .mJ eff~rcm limb of CN. X) .. _ -
_ 8. The carotid sinus reflex, in which pressure on the carotid sinus slows the hear r~te {br.ldycardia) (efferent 11mb oreN XJ
.~. XI;....THE A<?..c.E:.~ .. QBJ N_~~VE ~C~XI), or spinal accessory n~rve, is an SVE nerve (Fig _ lire 13-6). _ . _ . _. ..
A. General ("haracteristics. The a<;ces~ory nerve mediate's head and sho~lder movemenl and innervates the laryngeal muscles. It has the following divisions:
:1.. The cranial division (accessory portion), which arises from the nuCleus ambigum of the medulla. It exits the medulla (rom the-postolivary sulcus and joins the vagal nerye (CN X). It exits the skull through the jugular foramen with eN IX and eN X. I rinnervates the intrinsic muscles of rhe larynx through the inferior (r~current) laryngeal nerYe, with the exception of the cricothyroid muscle. . ..
2. 111~ spinal division (spinal portion), which' arises from the ventral horn of cervical segments Cl through C6. The spinal roots exit the spinal cord laterally between the \"entral and dorsal spinal roots, ascend through the foramen magnum, and exit the skull through the jugular foramen. It innervates the sternocleidomastoid muscle with the cervical plexus (E-2-) and the trapezius muscle with the i:en'kal plexus (C-3 and C-4).
B. Clinical correlation. Lesions cause the following conditions:
I----t-Facial nucleus in pons
Ambiguus nucleus in medulla ----f--f-
• CN IX--7'
-f---t--- Accessory- nucleus CN X ---'---1---(1 _ in spinal cord (C1-CS)
CNIX---<",I CNXI /
Figure :13-6. Thc cranial and spinal divisions tlj the accessory nerve (cranial nerve (eN) IX). The·cranial Ji\'isi{11l hitchhikcs a ride.: with thc lICCCssory ncrvc,thcn joins the vagal ncrve to become the inferior (recurrent) bryngcal nervc. Thc rc:curn::nt laryngcal nervc innervatcs the intrinsic muscles of the larynx, except for the cricothyroid musclc. The spinal division inncrvilles rhe trapewid :mJstcrnocleidomastoid muscles. Three nerves I'a:.s throll!.!h thc jugular (c}ram<:n (glomus jugularc [UIlHlr).
= . .".,: Cd "Yi_' 'C n "S.MtM.',
76 Chapter 13 I 1. Paralysis of t~e sterm.'lcleidomastoid· muscle (har rc~ults in difficulty in [uming I
the heaJ to the contralateral side .
2. Paralysis of the trnpe:ius muscle thm r~~lIlts in shoulder droop nnd inability to I
3. Paralrsis of the larynx if [he crClninl root is in\'ol\'ed
Motor cortex
. . I Corticobulbar traC;.t ~ I'
Hypoglossal nucleus
Medulla
Pyramid
A
LMN
.....
\/ .. 1
-UMN
C!>-- CorticobuJar tract
UMN lesion
~' (spastic paralysis)
Decussation ~ I
8
I LMN
LMN lesion' (fla9cid paralysis)
Figure 13-7. Motor inncrvalil11l of the longue. COJlicohulhar fibers projcCll'redoll1in;lntiy to the contralateral hYl'_'gloss:11 nllclcll.~. An upper llluCOr Ileuron (U,\1N) Icsi(ln C<lllses deviatiol1 (l( the protruded tongue to the \\'c"k (c,'!\trnlatcral) ~idc, r\ lower tt\(lt(lr l\l'lIrOI1 (UdN) Ic~i()n C;l\l~CS dc\"i;ltiol1 pf the- \"": fuded t\\) :;;,1:' 10 tht: \\':lk (i!"U;llcr:d) .~idc. (/\) Norllul r\lnl~IIl'. ([3) T(lni~lIl' 11"1[11 U~lN ::Iid L\H'! !:.,i",:,
I I
·1 I I I I I I I I I I I I I
I I I I I I
.. .• z ... ': .. :- .. "
" . : .
Cranial ~erves' 77 .. . . .. ................................... : .............. : ............................. "' ................. : ........................................................................................................ . XII. THE HYPOGLOSSAL NERVE (eN ~is a GSE nerve (Figure 13.7). ~·tt· F .1.", d' . . • eneral characteristics. The hypoglo.::.::nl nerve me lates tongue movement. It ames
from the hypogloSsal. nucleus of the I\l~dulla nnd exits [he medulla in the preolivary sulcus. Ie exits the skull through the hn"\oglossnl cC1nnl, nnd it innervates the intrinsic and extrinsic muscles \.,f the. ~ongue. Extrinsic muscles are the genioglossus, Sty. loglossus, and hyoglossus.
. ,
B. Clinical correlation
:to Tr~nsection results in hen1ipamlysis of the tongu'e.
2. Protrusion causes the tongue to point toward the weak side because of the unop. posed action of the opposite genioglossus muscle,
A. ~!edial medullary syndrome (anterior spinalaner), syndrome). Affected structures and re$ultant deficits include:
:1.. The corticospinal tract (medullary pyramid). Lesions result in conrralarernl spas, tic hemiparesi5.
--~"'- 2. The-medial lemniscus. Lesibnnesu1c"in C6htr~Iareranoss of tactile and \1bracion semation frOhl the trunk and e~tremities.
3. The hypoglossal nucleus or intraa.-~ial root fibers [cranial nerve (eN) XII]. Lesions result in ipsilateral t1accid hemiparalysis of the tongue. \Xlhen protruded, the rongue points ro the side of the lesion (i.e., the weak side). See Figure 13,7.
Vestibular nuclei
Inferior cerebellar peduncle
Spinal trigeminal tract and nucleus _-;----<:::!:.:
CNX
Nucleus ambiguus
Lateral spinothalamic tract
'. Nucleus of SOlitary tract
Dorsal motor nUCleus of eN x
.--
B
FI gu r e :1.4-:1.. V"" u ,., b;o", oi .I" """b '" 'n; ;>, 'he levd or, he hI"""''''';>' n .. clem or c '" n;;>' nen'e (eN) XII ;",d the dors;1/ motor nltc!CU\ p(eN X. (A) ~!t'\li:t! Il1cdu!hry syndrome hl(cri,t/ ~pin,t/ 'lr(ery). ([3) Latern! mcdllllary fPO~tcri()r in(cri()r (<:r<:h<:ll:lr artl'ry (f'iC_\)) S)"IHlroI11c.
.1 I I I I I I I I I I I I I I I I I I I
': ...
lesions of the Brain Stem 79 •••••••••••••••• ~ •••••••••••••••••••••••• l •• : ................................................ : ......... _ .............. ..: ......... :._ ................................................................. : ••••••••••••• ~.
B. Lateral medullar)' syndrome [posterior inferior cerebellar artery (PICA) syndrome] is ch~lracrerized by dissociated sensory loss (see I.B 6-7). Affecred strllC.tllres nnd re. sulcanc.deficits include: .
:1. The vest.ibular nuclei. Lesions re!lult in nystagmus, nausea, vomiting, andverrigo.
3. The nucleus ambiguus of CN IX, CN X, and eN XI. Lesions result in ipsilateral laryngeal. pharyngeal; and palatailleqiiparalysis [Le .• loss of the gag reflex (effer. enc limb), dysarthria, dysphagia, and dysphonia (hoarseness)].
4. The glossopha~ryngeal nerve roots. Lesions result in loss of the gag reflex (afferent limb).
5. The vagal nerve roots. Lesions result in the same deficits- as seen in lesions in~. \'oh'ing the nucleus ambiguus (see I B 3).
6. The spinothala~ic tracts (spinal lemniscus). LeSIons' result i~ contralateral loss of pain and temperature sensation from the trunk and extremities.
7. The spinal trigeminal nucleus and tract. Lesions result in ipsilateral loss of pain and temperature sensation from the face (facial hemianesthesia).
8. The descending sympathetic tract. Lesions result in ipsilateral Homer's syndrome (i.e., ptosis, miosis, hemianhidrosis, and apparent enophthalmos).
II. LESIONS OF THE PONS (Figure 14·2A)
_~~ ... ,M.~_~~l inferior pontine,~r~~..9.El~ results from occlusion of the paramedian branches of the baSIlar artery:~Affeceed structures and resultant deficits include:
i. The corticospinal tract. Lesions result in f.ontralateral spastic hemiparesis.
2. The medial lemniscus. Lesions resule in conrralateralloss of tactile sensation from the trunk and extremities.
Spinal trigeminal nucleus and tract --'-'r--=-H-
eN VIII (vestibular nerve)
CNVII
Lateral spinothalamic tract
• CNVI
Corticospinal tract
A
FIgure :14-2. Vascular lesions of the caudal pOllS at the level of the nhduccnt nucleus of cranial nerve (CN) VI and the fncinl nucleus of CN VII. (A) MeJial inferior pontine syndrome. (0) Latcrnl inferior pontine syn(./rome (anterior inferior cerehellar artery (AICA) syndrome}. (C) MeJial longitudinal fasciculus (MLF) syn:1:s:-:-::.
m b' '7n-,,5 Oat 5
__ TZ
t _
·1 80 Chapter 14 I ........................................................................................................................................................................................................... . . .
3. The abducent nern! roots. Lesions result in ipsilaceral lateral reccus par,llysis. I §., , Lateral inferiot:J!Qntin~ syndrome ("nterior inferior ccrebeUar mtery (AICA) $)'n~
j.. Th~ 'facial nucleus and intraaxial nerve fibers. Lesions restilr in: a •. Ipsilnreral f<lcial nen'e pctralysis b. Il-~sihlteralloss·l,."If taste from [he anterior t\\'o~thirds of the tongue c. Jpsilmeralloss of lacrimation and reduced salhr.ation d. Loss of comea1 and smpedial reflexes (efferent limbs)
I I
2. The cochlear nuclei and illtraaxial nerve fibers. Lesions result in unilateral cen; I tral deafness.
3. The \"esti~ular nuclei and intraa?,ial nerve fibers. Lesi~ns result in nyscagmus., nausea,_\:Qmiting, and,·ertigo. ' ... ~..' " ,,_,', .. ',' '
4. Th~ spinal trigeminai nu~i~~~ '~:~t;1i!·c~~·L;~~~ns ·r~s~l~· ~~'·~~~i·l~·t:~;;n~~;·~f·~~in and temperature sensation fron) the face (facial hemianesthesia).
5. The middle and inferior cerebellar peduncles. Lesions result in ipsilaceral limb and gait dysraxia.
6. The spi~~t~,:l~~!~.tracts (spinallemnisc~f~): Lesions. r~~lJ.ltin c9nlJ.:?J?~era! loss of pain ana temperature sensation from the trunk and extremities. _.: .. _ .. " .
7. The descending s)mpathetic tract. Lesions result in ipsilateral Horner's syndrome.
c. 11~.Q.i.<!tJongitudinaLfq.s.~..i.culu~jl'.!LF1 ... ~.I.~drome (internuclear ophthalmoplegia) ._'-- [see Figure 14;2C] interrupts fibers from the contralateral abducent nucleus that pro~.
jeet, through the ~·1LF. to the ipsilateral medial rectus subnucleus of CN Ill. It c'auses medial rectus palsy on attempted lateral conjugate ga:e and nystagmus in the abducting eye. Con\'ergence remains intact. This syndrome is often seen in patients with multiple sclerosis. . .
D., ... FaciaLcoUiculus syndrome usually results from a pontine glioma or a vascular acci_... dent. The internal'genu ofCNVII and the nucleus of CN. VI underlie the facial col-
lieu Ius. .';
i. Lesions of the internal genu of [he facial nerve cause: a. Ipsilateral facial paralysis b. Ipsilateral loss of the corneal reflex
2. Lesions of the abducent nucleus cause: a. Lateral rectus paralysis b. Medial (coO\'ergent) strabismus c. Horizontal diplopia
III. LESIONS OF THE MIDBRAIN (Figure 14~3)
A. Dorsal midbrain (Parina~dts) syndrome (sc7'Figurc.14-JA) is often the resulr of ~ pinealoma or germinoma of [he pineal region. Affected structures and rcsulrarH defIcits include: . . :1. The supcrior colliculus and pretectal area. Lesions calise paralysis of upward and
downward gaze, pupillary disturbances, and absence of convergence.
2. The cerebral aqueduct. Compn.'ssion Crluses noncl)ll1ll1unicating hydroccph~lus.
Posterior commissure and center for vertical conjugate gaz~
CN III
Superior colliculus
Nucleus of CN III
~,....,..~ Spinothalamic tract .
Mediallemrtiscus
Dentatothalamic tract
Red nucleus
Figure 14-3. Lesions of the ~ostn11 midbrain at the lev~l of the superior col\iculus and oculomotor nucleus ,,'\t' cranial nen'e (CN~ III. (A) Dorsal midbrain (Parinaud's) s~ndrome. (B) Paramedian midbrain (Benedikt) syn.. iwllle. (C) }'1edial midbrain (\'Veber) s)ndrome.
. 1.. The .oc:ulomotor nen'e roots (intraa.xial fib.ers). Lesions cause complete ipsilateral oculomOtor"paralysis. Eye abduc~ion and depression is caused by the intact lateral .. rectus (eN VI) and superior oblique (eN IV) muscles. Ptosis (paralysis of the levator palpebra muscle) and fixation and dilation of the ipsilateral pupil (complete internal ophthalmoplegia) also occur.
2. The dentatothalamic fibers. Lesions caus~ contralateral cerebellar dystaxia with intention tremOf.
3. The medial lemniscus. Lesions result in contralateral loss of tactile sensation from the trunk and extremities.
C. Medial mid~rain (Weber) syndrome (see Figure 14-3C). Affected structures and re-sultant deficits include:. :--.
1.. The oculomotor nerve roots {intraaxial fibers}. Lesions cause complete ipsilateral oculomotor paralysis. Eye abduction and depression is caused by intact lateral rectus (eN VI) and superior oplique (eN IV) muscles. Ptosis and fixation and dilation of the ipsilateral pupil also occur.
2. The corticospinal tracts. Lesions result in contralateral spastic hemiparesis.
3. The corticobulbar fibers. Lesions cause contralateral weakness of the lower face (eN VII), tongue (CN XII), and palate_ (eN X)"The ·upper face division of me facial nucleus receives bilateral corticobulbar input. The uvula and pharyngeal wall are pulled coward the normal side (eN X), and the protruded tongue points to [he weak side. ..-
,/ IV. ACOUSTIC NEUROMA (SCHWANNOMA) (Figure 14-4] is a benign tumor of
Schwann cells [hat affects the vestibulocochlear nerve (eN VllI). It accounts for 8% of all intracranial tumors. It is a posteri~r fossa tumor of the internal auditory meatus and cerebellopontine angle. The ~curoma often compresses the facial nerve (eN VII), which accompanies eN VIIl in [he cerebellopontine a.ngle and internal auditory meatus. It may impinge on the pons and affect the spinal trigeminal tract (eN V). Schwannomas occur twice as often in females as in tn"les. Affected structures and resultant deficits include:
Figure :14-4. ~1agnetic resonance image of an acoustic neuromao This coronal section shows dilation of the \Oentricleso The \Oestibulocochlear nenoe is \Oisible in the left internal auditory meatuso The tumor indents the lateral Fonso Cranial nenoe (C~) palsies include CN V, VII, and VIIIo Symptoms inClude unilateral deafness, facial anesthesia and weakness, and an absent coronal reflexo This is a Tl-weighced imageo
• ", .
A. The cochlear nen'e of eN VIII. Damage results in tinnitus and unilateral nerve deaf-" ness,
B. The vestibular nen'e of CN VIII. Damage results in vertigo, nystagm~'~, nausea, vomiting, and unsteadiness of gait,
C. The facial nerve (eN VII). Damage results in facial weakness and loss of the corneal reflex (efferent limb). /
D. The spinal trigeminal tract (eN V). Damage resulcs in paresthesia, anesthesia of the . ipsilateral face, and loss of the corneal reflex (afferent limb),
E. Neurofibromatosis type 2 often occurs with bilateral acoustic neuromas.
v. JUGULAR FORAMEN SYNDROME lIsunlly results from'"n pos"terior fossa tumor (e,g., glomus jugu(are tumor, the most common inner em tumor) thnt compresses CNIX, X, and XI. Affccted structures anq resultant deficits inc"lu"de: '
A. The glossopharyngeal nerve" (CN IX). Di1ll1ng{results in:
j.. IpsilCltcralloss of the gng reflex
2. Ipsilaccralloss of pain, tcmpcrature, and taste in (he tongue
B. Thc vagal nerve (eN X). Dam;)ge results in:
1. Ipsibrcri11 p;]r;llr~is of rhe soft p:11:!tc ;md larynx
2. II'"iI:ltcr:1! !(Jc;s (;( ,he: ,(/;lg rcfh-x
I I I I I I I I I I I I I I I I I I I I
.....
lesions of the Brain Stem 83 .............. : .......................... : ......•................ :.-.. __ .;.: ......... ; ... .; •............................ , ............. : ................................. ··········~ .. ··············· .. ·t· ..... _ C. The nccess(.,ry .ner~·e (eN Xl). Damage re~ults in:
:L Pnmlysis of the sternocleidomastoid muscle,.which results in the inability to tum· the heaJ rothe l'rrosit~ side .
2. Pamlysis of the (rnre:ius muscle, which causes shoulder droop and inability to shrug· the shoulder
. . VI.· "LOCKED-IN" SYNDROrv'lE is a lesion of the b~se of (he pons as the result of infarc-'
tion, trauma, tumor, or dem):elinad9n. The corcic?~pinal artd corticobulbar tr(l.cts are af-
. ECA
Aorta
A n
Figure 1.4-5. Anatomy of the subclavian steal syndrome. Thro~bosis of the proximal pare of the subclavian artery (lefc) results in retrograde blood flow through the ipsilateral vertebral arcery and into the left subclavian artery. Blood can be shunted from the right vertebral ar~ery and down the left vertebral artery (A). Blood may also rench the left vertebral artery througn the carotid circulation (8). ACA = anterior cerebellar arteryi ACOM = anrcrior communicating arteryi AICA = anterior inferior cerebellar arteryi ASA = anterior spinal arteryi BA = basii.lr arterYi BCT = brachioccphalic trunk; CCA = common carotid artery; ECA = extcrnal carotid .arteryi ICA = internal carotid arteryi MCA = middle cerebral arteryi PCA = posterior cerebral arteryi PCOM = postcri~)r communicating arceryi PICA = posterior inferior cerebellar arterYi SCA = superior communicating artery; SCLA = subclavian :uteryi VA = vcrtebral areery. .
I --I
84' Chapter 14- I ............................................................................... -;, ........................................................................................................................................ -
CENTRAL PONTINE MYELINOLYSIS is a lesion of the base of the pons thm nffects th (\.,rrico:'l'inal nnd corticobul~.lrtmcts. More than 75% ofcnses are nsso~imed \\lith nlcoholi51' , \,'r mpid. correct h.:'" of h)1'onacremia .. Symptoms include spastic qundripnresis. pseudobllUx1
VIII.
r.1hy. and ment.,l chang~s. Thi~ condition may become the locked*in s~'ndrome ...
"TOP O'F THE BASilAR" SYNDROME res~lts fro;n embolic occl~sion of the roSti.l l:-.l:,ilar nrter,),. Neurologic sigll$ include ortic ataxia and psychic paralysis of fixntkm of g~: (Balines syndrome), ectork rurils. somnolence. and conical blindness, with or \\'ithou "isual <1l1osogno:,ia (Anton's syndrome).
I I
IX. SUBCLAVIAN STEAL SYNDROME (Figure "14-5) result:s"from thrombosis of the let sul:-cla\"inn artery proximal to the "errebtal artery. Blood is shunted retrograde down thl left ,-ertebral artery and' into [he left sl,Ibclavian' artery. Clinical signs include transien weakness and claudication of the left ann on exercise and "ertebrobasilar insufficienc: ~ i.e .. ,·errigo. di::iness).
X. THECEREBELLOPONTINE ANGLE is the junction of the medulla. pons. and cere hellum. CN VII and VIII are found there. Five brain rumors, including a cyst. are .. often 10· ..:ated in the cerehllorontine angle cistern. Remember the acronym SAME: sch\\'annoIDc(7590), arachnoid cySt (1%), meningioma (10%), ependymoma (1 %), and epidermoiL (5%). ll1e percentages refer to cerebellopontine angle tumors.
I I I I , I I I I I I I I
I I I I I I I I I I
--~--------' --. ----~~~-----
.' . .... :-' . . ' /., ....
. . -.
-. '-.
1.5 Cerebellunl
f. FUNCTION. The cerebe~Ium has thr~e primary functions: . . A. Maintenance of posture and balance ,
B. Maintenance of muscle tone
C. Coordination of voluntary motor activity
II. ,ANATOMY
A. Cerebellar peduncles
2. The superior cerebellar peduncle contains the major OUtPUt from the cerebellum, the dentatothalamic tract. This tract terminates in the vent:rallateral nucleus of the thalamus. It has one major afferent: pathway, the ventral spinocerebellar tract.
2. The middle cerebellar peduncle receives pont:ocerebellar fibers, which project to the neocerebellum (pomocerebelIum). :.'
3. The inferior cerebellar peduncle has three major afferent tracts: the dorsal spinocerebellar cract, the cuneocerebeIIar tract, and the olivocerebellar tract from the • ~ont:ralateral inferior oIi\'ary nucleu.s. " . ".
8. Cerebellar cortex, neurons, and fibers
:1.. The cerebellar cortex has three layers.
a. The molecular layer is the outer layer underlying the pia. It contains stellate cells, basket cells, and the dendritic arbor of the Purkinje cells.
h. The Purkinje cell layer lies between the molecular and the granule cell layers. c. The granule layer is the inner layer overlying the white matter. It contains
granule cells, Goigi cells, and cerebellar glomeruli. A cerebellar glomerulus consists of a mossy fiber rosette, granule cell dendrites. and a Goigi cell axon:
2. Neurons and fibers of the cerebellum
a. Purkinje cells conve}, the only output from the cere'bellar cortex. They project inhibitory outPUt (i.e., 'Y-aminob.uiyric acid (GABA)J to the cerebellar and vestibular nuclei. These cells me' excited by parallel and climbing fibers and inhibited by GABA-ergic basket and stellate cells.
b. Granule cells ex<;ite (by w~y of glutamrtte) Purkinje, basket, stellate, and Golgi cells through p;1rallcl fibers. They nre inhibited by Golgi cells and excited by mossy fibers.
c. Parallel fibers (lre [he nxolls of granule cells. These fibers extend into the molecular farer.
n Mossy fibers arc the afFerent excitnrory fibers of the spinocerebellar. pomo-
C. Th~ ventr.~l late~1 nucleus of the. thala~us receives the dentatothalamic tract. It pn.lj~~[s r"l rht! primmr motor correx of the precentral gyrus (Brodmann's area 4). .. . .
D. The motor cortex (motor strip, or Brodmann's area 4) receives input from the ventral bteral i·lUdell:> of the thabmus: Ie projects as the corticopontine tract to the pontine nuclei.
E. Tl~e pontint! nuclei receh·e input fr~m the motor cortex. ~xons project as the pomo.cerebellar tract to the contralateral cerebellar cortex, where they terminate as mossy .fiber::. thu:: c.on~pleting the circuit.
IV. CEREBELLAR DYSFUNCTION includes rhe following triad:·
A. Hypotonia is loss of the resisrance normally offered by muscles to palpation or passive maniruiation. It results, in a floppy, ioose-jointe<J, rag-doll appearance with pendular retlexes. The, patient arrears i,nebria~ed.
B. Dysequilibrium is loss of balanc~ c.haracteri:ed by gait and t~nk dystaxia. . '. C. Dyssynergia is loss of coordinated muscle activity. It includes dysmetria, intention
tr'emor, failure to check movements, nystagmus, dysdiadochokinesia, and dys, rhythmokinesia. Cerebellar nystagmus is coarse. It is more pronounced when the patient looks towa~d the side of the. lesion. . .
V. CEREBELLAR SYNDROMES AND TUMORS
A. Anterior vermis syndrome inv6ives the leg region of the anterior lobe. It results from atrorhy of the romal vermis, most commonly caused by alcohol abuse. It causes,gait, trunk, and leg dystaxia.
B. Posterior vermis syndrome involves the flocculonodular lobe. It is usually the result of brain tumors in children and is most commonly caused by medulloblastomas or ependymomas. It causes truncal dystaxia. ,',.
C. Hemispheric syndrome usually involves one cerebellar hemisphere. It is often the result of a brain tumor (astrocytoma) or an abscess (secondary to otitis media or mastoiditis). It causes arm, leg, and gait dystaxia and ipsilateral cerebellar signs.
D. Cerebellar tumors. In children, 70%· of b~ain tumors are found in the posterior fossa. In adults, 70% of brain tumors are found in the supratentorial compartment.
1. Astrocytomas constitute 30% of all brain rumors in children. They are most: oft:en found in the cerebellar h~misphere. After surgical removal, it is common for the child to survive fO,r many years. '
2. ?-"1edulloblastomas are malignant and constitute 20% of all brain tumors in children. They are belleved to originate from the 5uperfici?1 granule layer of the cere' bellar cortex. They usually obstruct the passage of cerebrospinal fluid (CSF). As a result, hydrocephalus occurs.
3. Ependymomas constitute 15% of all brai~ tumors in children. They occur most frequendy in the fourth ventricle. TheY usually obstruct the passage of CSF and cause hydrocephalus.
I. INTRODUCTION. The thalamus i.s the l~rgest diviSion of the diencephalon. Ic-plays al important role in the integration of the·sensory and motor systems.
II. MAJOR THALAMIC NUCLEI AND THEIR CONNECTIONS (Figure 16-1)
I , I , I I
A. The anterior nucleus receives hypothalamic input from the. mamillary nucleu: I through the mamillothalamic tract. It projects.ro the cingulare gyrus and is part, of lht Pape: circuit of emotion of the limbic system. . ..
B. The mediodorsal (dorsomedial) nucleus is reciprocally connected to the prefrontal I cortex- It has abundant connections with intralaminar nuclei. It receives input from the amygdala. substantia nigra, and temporal neocortex. When it is destroyed, memory loss occurs (Wemicke-Kqrsakoff syndrome). The mediodorsal nucleus plays a role I , in the expression of affect, emotion, and behavior (limbic function).
C. The centromedian nucleus is the largest intralaminar nucleus. It is reciprocally connected to the macor cortex (Brodmann's area 4):.The centromedian nucleus receives input from the globus pallidus. It projects to the striatum (caudate nucleus and putamen) and projects diffusely to the entire neocortex.
D. The pulvinar is the largest thalamic nucleus. It has reciprocal connections with the association cortex of the occipital, parietal. and posterior temporal lobes. It receives input from the lateral and medial geniculate bodies and the superior colliculus. It plays a role in the integration of visual, auditory, and somesthetic input. Destruction of the dominant puh-inar may result in sensory dysphasia.
E. Ventral tier nuclei
:1. The ventral anterior nucleus receh-es input from the globus pallidus and substamia nigra. Ie projects diffusely to the prefrontal cortex, orbital cortex, and premotor cortex (Brodmann's area 6).
" :
2. The ventral lateral nucleus receives input from the cerebellum (dentate nucleus), globus pallidus, and substantia nigra. It proje,cts to the n.1otor cortex (Brodmann's area 4) and the supplementary motor cort~)((Brodmann's area 6).
3. The ventral posterior 'nucleus (\'entrob~al complex) is the nucleus of termination of general sommic afferc'nt (touch. pain. and temperature) and special visceral afferent (caste) fibers. It h:lS twO' subnllclei. a. The ventral posterolateral nucleus receives the spinothalamic ,tracts and the
medial lemniscus. It projects to the somesthetic (scn~t)ry) cortex (Brodmann's CHC;lS 3, 1, :lnJ 2).
b. The vcntral posteromedial (VPM) nuclells receives the trigcminoch:ll;<mic tf:H:(<; ;md projeCTS to the ~OlT1l'sth('tic (sen:,()ry) corte.; (Bnic1m:ll1n'.; ;Ii ~.:"" 1. ;111d /). "I'lle ~~\;~,r~q('q-'! ((;·!:.:~('1 r,' ldl\I;;'IY ()C;j<rL (;: ':) d~· _;;.·:i·~, .:
Figure :16-:1. ~'1ajor thalamic nuclei and their connections. (A) Dorsolateral aspect and major nuclei. (B) l\1ajor afferenr and efferent connections, VA = ventral anterior nucleus; VL = venrrallateral nucleus; VPL = "entral posterior lateral nucleus; VPM = \'entral posterior medial nucleus. .
. projects via the central tegmental tract to VPM, and thence to the gustatory cortex of the postcentral gyrus (Brodmann's area 3b), of the frontal operculum and insubr cortex. The taste pathway is ips!lateraL· ..
F. Metathalamus
:to The lateral geniculate body is a visual relaY,11ucleus. It receives retinal input through the optic tract and projects to the prim~~'visual cortex (Brodmann's area 17).
2. The medial geniculate body is an auditory relay nucleus. It receives auditory input through the brachium of rhe inferior colliculus and projects to the primary auditory correx (Brqdmann's nre;-.s 41 and 42).
G. TIle reticular nucleus of thalamus surrounds the thalamus as a thin layer of -y-aminobutyrie rlcid (GABA)·ergic neurons. It lies between the external medullary lamina and the internal capsule. Ie receives excitatory collateral input from conieothalamic and thalamocortical fibers. It projects inhibitory fibers to thalamic nuclei from which it receives input. Ie is thoughr to playa role in norm:1l c1ectroencephaolgram readings.
,0',- S't a UN.t
90 Chapter 16 ............................................................................................................................................................................................................. III. BLOOD SUPPLY. The thalamlls is ir:rigmeJ: 1:-r three arreries (sec Figure 3~3).
A. B. c.
The posterior communicating. artery
Th~.posterior cerebral artery
The anterior choroidal artery (bteral geniclilate body) . .
1 I I I
IV. THE INTERAL CAPSULE (Figure 16·2) is a layer of white matter (myelinated axons) [h;1 I ~erarates [he caudace nucleus and che tl}alamusmedially froll-i the lentiforin nucleus lacerally
A. The anterior limb is locaced between [he caudnce nucleus and the lentiform nudeu I (glol:-us pallidus and putamen).
B. The genu contains the corticobulbar fibers.
nle posterior limb is located between the thalam'us and' the lentiform micleus. It con .1 rains corticospinal (pyramid) fibers ~s well as sensory (pain, temperature, and touch)
c. visual. and auditory radiations. .
D. Blood supply I :to TIle anterior limb is irrigated by the medial striate branches of the anterior cereera:
artery and the lateral striate (lenticulostriate) branches of the middle cerebral artery.
2. The genu is perfused either by direct branches from the internal carotid artery or /:-Y'pallidall-ranches of the anterior choroidal artery.
3. The posterior limb is supplied by branches of the anterior choroidal arrerJ' an~ lenticulostriate branches of the middle cerebral arteries.
Caudate nucleus --.'--
Genu
Corticobu!bar fibers -~--,H--+-)
Posterior limb --f----+-t--
Thalamus --t------'
Sensory radiations from VP nucleus to areas 3, 1, 2
Medial geniculate body (audition)
Lateral geniculate body (vision)
Globus pallidus
Pulamen
Corticospinal fibers
Auditory radiation tv transverse .' temporal gyri of Heschl
. (areas 41 and 42)
Visual radiation to sl.riate cortex of occipital lobe (area 17)
Figure 1.6·2. Hnri:OlHal scctil'll d the right intcrnal c;11'~\l1c ~ho\\'in~: the major fiber projections. Clinically impnrt<lnt tract~ lic in the genu ;md l""~\(:{i(\f limh. L",i\\\\~ (/ (he intcrn;d C\I':ilJ!e C\lISC CL'nrraiater;!1 hcmi~';H<:\is ;lnd c{)(\tr,d:1(cr:d hcrni:\I\<.I!'i;\. \·T c ·· .. ·.-·:·"r;': I',';:",; Ie ",·"Ic",.
I.. INTRODUCTION. The visual ::y::tem is sen'ea by the optic nerve, which is 'a ::pecial somatic afferent nerve.
II. THE VlSUAL PATHWAY (Figure 17·1) includes the following structures,
A. Ganglion cells of the retina fonn the optic nerve [cranial nerve (eN) IIJ. They project from the nasal hemirerina to the contralarerallateral geniculate body and from the temporal hemiretina to the ipsilateral lateral geriiculate body.
•
Nasal' Nasal Temporal
0·0 (~)90
~o~
~11~ -+-+-H-4-- Lateral geniculate
body
Visual radiation to lingual gyrus
Visual radiation to cuneus
~--+"'---- Visual cortex area 17
Flgure 17-1. The visual pathway from the retina to the visual conex showinl:: visual field defects. (I) Ipsilateral blindness. (2) Binasal hemianopia. (3) Bitemporal hemianopill. (4) Right hemianopia. (5) Right upper quadranranopia.(6) Right lower quadrantanopia. (7) Right hemianopi:t with macular sparing. (8) Left constricted field as a result of end-stage glaucoma. Bilateral constricted ~c1ds may be seen in hystcria. (9) Left central scotoma as : :::~;~ ;~ vp~;': {rctrobulb:tr} neuritis in multiple sclerosis. (10) Upper aititudinal hcmianopia as a rcsulr of bilateral dc.!>tnJc(ion of the lingual gyri. (11) Lower nltitudinal hemianopia as n rc:\ult (If hiLHer,,1 destruction of the cunei.
I -- .m PSZ _em 7!"'N'!t '1 . '.
I 92 Chapter 17 . . ................................................................................................................................................................................................................
B. The optic nen'e rrojec(s from the l:nnina cribrosa (,{the scleral canal, through the t
c.
tic c.:~'\nal. t\.l:the\.~~"\tic chiasm. .
1.~ Transection callses ii'silatcral blindness, with no direct pupillary light reflex.
2. The section ,-,f the \.lptic nCr\'e "nhe optic chiasm transects all fibers (roin the i :;ilmeml retin~' as weI.! as fibers from the contralateral inferior nasal qundmnt t!. loop into the \."Irtic nerve. This lesion cnuses ipsilateral blindness and a COntra\; era} urp~r temroral quadrant defect (junction sc.otoma).
The optic chiasm conrnins decussating fibers from the two nasal hemir.etinas. It co rains noncrossing fibe:s from the c\\'o temporal hemirecinas and projects fibers t:O ti suprachiLlsmatic nucleus of the hypothalamus.
I I I I
1.. lvlidsagittal transection or pressure (often from a pitu itary tumor) causes bi ten .1 poral hemianoria. . . .
D. The optic tract contains fibers from the ipsilateral temporal hemiretina and th contralateral nasal hemiretina. Ie projects to the ipsilateral lateral geniculate bod- I pretectal nuclei. and superior colliculus. Transection causes contralateral hemi
E. The lateral geniculate body is a si;<-Iayered nucleus. Layers 1,4, and 6 receive crosse( fibers; layers 2. 3. and 5 receh'e uncrossed fibers. The lateral geniculate body receive input from layer VI of the striate cortex (Brodmann's area 17). It also receives fiber from the ipSilateral temporal hemiretina and the contralateral nasal hem ire tina. I projects through the geniculocakarine tract to layer IV of the primary visual corte~ (Brodmann's area 17).
I
F. The geniculocalcarine tract (vi;uar radiation).. projects through two divisions to the visual cortex. I.
:to The upper di"'ision (Figure 17-2) projects to the upper bank of the calcarine suI· cus, the cuneus. It contains input from the superior retinal quad1"ants, which rep· resent the inferior visual field quadrants. a. Transection causes a contral.aterallower quadrancanopia. b .. Lesions that involve roth cunei cause a lower altitudinal hemianopia (alti·
tudinopia).
2. The lower division, (see Figure 17-2) loops from rhe lateral geniculate body anreriorly (Meyer's loop), then posteriorly, to terminate in the lower bank of the calcarine sulcus, the lingual gyrus. It contains input from the inferior retinal quadrants, which represent the superior visual field quadrants. a. Transection causes" contralateral upper quaCIrantanopia ("pie in the sky"). b. Transection of both lingual gyri causes an upper altitudinal hemianopia {al-
titudinopia}. . .
G. The visual cortex (Brodl~lann's area 17) is.l~cntcd on the banks of the calcarine fiS
sure. The cuneus is the upper b.lnk. The lingual gyrus is the lower bank. Lesions 'cause contralateral hemianopi;l with m:1:lIlar sp:uing. The visllal cortex h<ls a rctinotopic organization:
1.. The posterior area rcccin:s macul:lr inrut (c('ntral vision).
2. The intermediate arca recein's paro1lll;Ktd:1f input (pcriphef:11 inptlr).
3. The anterior area reCl'i\'l-~ I1lClI1()cuhr !:'i".!r.
Lesion A 01 visual radiations to' sup.bankofcakarinesu~s
I
/ I
/
I I I Field defects
Lower r. ho"monymou5 quadrantanopia
caJcarine~ sulcus B ~
Upper r. homonymous quadrantanopia
Lesion B of visual radiations to int. bank of calcarine sulcus
Figure :1.7-2. Relations of the left upper and left lower divisions of the geniculocalcarine tract to the 12.cera: \'erltricle and calcarine sulcus. Transection of the upper'division (A) results in right lower homonymous quaeramanopia. Transection of the lower division (B) results in right upper homonymous quadranta.rlOpia. (Reprinted with pennission from FLx jO: BRS Neuroanatomy. Baltimore, Williams & Wilkins, 1997, p 261,)
III. THE PUPILLARY LIGHT REFLEX PATHWAY (Figure 17-3) has an afferenc lim'= (eN II) and an efferent limb (eN III). It includes the following structures:
A. Ganglion cells of the retina, ,,,,hich project biiaterally to the pretectal nuclei
B. The pretectal nucleus of the midbrain, which projects (through the posterior commissure) crossed and uncrossed fibers to ,the Edinger-\Vestph3.l nuclel!s
. . C. The Edinger-\Vestphal nucleus of eN III, \\lhich gives rise to preganglionic parasym
pathetic fibers. These fibers exit the midbrain with eN III and synapse with postganglionic parasympathetic neurons of the ciliary ganglion.
/
D. The ciliary ganglion, which gi\;es rise to postganglionic parasympathetic fibers. Tnes:: fibers innervate the sphincter muscle of the iris.
IV. THE PUPILLARY DILATION PATHWAY (Figure 17-4) is mediated by the sympathetic division of the autonomic nervous system. Interrupt:ion of this pathway at an y level causes ipsilateral Homer's syndrome. Ir includes the following structures:
A. The hypothalamus. Hypothal:llllic neurons of ,the paraventiicular nucleus project directly to the ciliospinal center (Tl-T2) of Yie intermediolateral cell column of the spinal cord. ,-
B. The ciliospinal center of Budge (TI-T2) projects preganglionic sympathetic fibers through the sympathetic trunk [0 the superior cervical ganglion.
C. The superior cervical ganglion projects postganglionic sympathetic fibers through the perivascular plexus of the cmotiJ system to the dilator muscle of the iris. Poscg<lnglionic sympathetic fibers pa~s through the tympanic cavity and cavernous sinus and enter the orbit through the superior orbital fissure.
Figure :1.7-3. The pupillary light rathway.light shined inco one eye causes boch pupils co constrict. 111e resr..:-nse in the stimulated ere is called the direct pupillary light reflex. The resp~nse in the opp'osite eye is called the consensual rupillary light reflex. C)J = cranial nerve. '.
V. THE NEAR REFLEX AND ACCOMMODATION PATHWAY
A. The cortical visual pathway pr9jeCts from the prim~ry visual cortex (Brodmann's area 17) to the visual aS50Ciacion cortex (Brodmann's area 19).
8: The visual association 'cortex (Brodmann's area 19) projects through the corticotee tal tract to the superior colliculus and pretectal nucleus.
C. The superior coHiculus and pretectal nucleus project.to the oculomotor complex of the midbrain. This complex includes the following structures:
i. The rostral Edinger,Westphal nucleus, wl)ich mediaces pupillary constriction through the ciliary ganglion /.
2. The caudal Edinger-\Vcstphal nucleus, \~'hich medintcs contrnction of the ciliary muscle. This contmction increases the refractive powcr of the lcns. .
3. The medial rectus subnucleus of eN III, which mediares cOlwergcnce
VI. CORTlCAl AND SUBCORTICAL CENTERS FOR OCULAR MOTILITY
A. The front;)l eye flcld is locared in the posterior p:Hr o( the middle (ronrZ11 gyrus (Brodm;![lll\ ;Ire;l 8). it i()~uhr('s \,olunr;l:Y (:;;lcc!(lic) eyl' Ilhi\·(·!~'i-"li\.
Flashlight swung from right eye to left eye Looking straight ahead
o
-tifu. Looking right Looking lett Eyes converged Looking straight ahead
,- F
I t®. zt;D
E' G
Looking right' I i Looking up Eyes converged Looking lett and down
i I
H J
No ~aac:lon to light Eyes converged Eyes of a comatose p~tient Looking straight ahead
Figure j,. 7-4. Ocular mowr palsies and pupillary syndromes. (A) ~elative afferent (Marcus Gunn) pupil, left eye. (B) Homer's syndrome, left eye. (C) Internuclear ophthalmopl~gia, right eye. (D) Third-nerve palsy, Iefr eye. (E) Sixth-nerve palsy, right eye. (F) Paralysis of upward gaze and com'ergence (Padnaud's syndrome). (0) Fourth-nerve palsy, right eye. (H) Argyll Robertson pupil. (I) Destructive lesion of the right frontal eye field. U) Third-nerye palsy with ptosis, right eye.
. -
:1.. Stimulation (e.g., from an irritative lesion) causes contralateral deviation of the eyes (i.e., away from the lesion).
2. Destruction causes transient ipsilateral conjugate deviation of the eyes (i.e., to
ward the lesion).
B. Occipital eye fields are located in Brodmann's areas 18 and 19 of the occipital lobes. These fields are cortical centers for involuntary (smooth) pursuit and tracking movements. Stimulation causes contralateral conjugate deyia~ion of the eyes.
C. The subcortical center for lateral conjugate gaze is locafed in the abducent nucleus of the pons (Figure 17 -S). Some authorities place the "center" in the paramedian pon-tine reticular fonnation. / '
:t. It receives input from the contralateral i~ontal eye field.
2. It projects to the ipsilaterallate(al rectus muscle and, through the mediallongitudinal fasciculus (MLf), to the contralateral medial rectus subnucleus of the oculomotor complex.
D. The subcortical center for vertical conjugate gaze is located in the midbrain at the level of the posterior commissure. It is called the rostral interstitial nucleus of the MLF anu is associated with Parinaud's syndrome (see Figures 14--3/\ and 17-4F).
-'I ,... w elB src
7 Mf"~Q'1~'bM7lWCe: 'NIL :1
96 Chapter"17 I ................................................................................................................................................................. .; ............................................................... .
. " "
- Lateral rectus muscle-"
./~ .. i //.~: Bilateral MLF syndrome
- Left .
"A ~ f::~-.. , ......
~
Right -
I I I I I
Midbrain B iJ:~ '" .. ~~ I I . -+-
Convergence
C :e~ ~:S-" Patient with MLF syndrome cannot
Pons adduct the eye on attempted latera: conjugate gaze, and has nystagmus in abducting eye. The nystagmus is in the direction of the large arrow-head. Convergence remains intact.
I I I I
Figure :1.7-5. Connections of the poncine center for lareral conjugate gaze. Lesions of the mediallongitudi. nal fasciculus (]-"(LF) between [he abducent and oculomocor nuclei result in medial rectus palsy on anempteJ lateral conjugate ga:e and hori:ontal nystagmus in ~he abduccing eye. Convergence remaim intact {inser}. A unilateral MLF lesion would affect only the ipsilateral medial rectus. eN = cranial nerve. "
I VII. CLINICAL CORRELATION I
A. in MLF syndrome, or internuclear ophthalmoplegia,(see F;igure 17·4), there is dam- I age (demyelination) to the tv1LF between the abducent: and oculomoror nuclei. It causes medial rectus palsy on attempted lateral conjugate gaze and monocular hori· :ontal nystagmus in the abducting eye. (Convergence is ~orm"l.) This syndrome is I most commonly seen in"multiple sclerosis.,./
B. One,and,a,h,,1f syndrome consists ofbilllteralicsions of the MLF lind a unilateral Ie· sion of the abducent nucleus. On ,,(tempeed lateral conjugate gaze, the only muscle I that (unctions is the intact lateral rectus.
C. Argyll Robertson pupil (pupillary light-ncar dissociation) is the absence of a miotic reaction to light. borh direct lind consellSunl, with the prcscrvnrion of a miotic rcnc- I tion to nc;)r stimulus (nccoll1l11olhrion-cor1\'crgcncc). J r occurs in syphilis ;)nd diabetes.
D. Horner's syndrome is cml$~J by (rnnsectk"l" of the oculosymparhetic pathway at any ll!\'el (see IV). Thh; syndr~)me consists of miosis, ptosis, apparent enophthalmos, and h~mianhidrosi~. .
E. Relati~'e aaerent(Ma~cus Gunn) pupil resuits from n lesiori o(the optic nen·e. the afferent limb of the pupillary light reflex (e.g., retrobulbar neuritis seen in multiple sclerosis). The diagnosis can be 111ade \\'ith the swinging flashlight test (see Figure 17~ 4A).
F. Tra,nstentorial (uncal) herniation occurs as a result of increased supratentorial pressure, which is commonly c~'\used by a bmin tuinoror hematoma (subdural or epidural).
:1. The pressure cone forces the parahippocampal uncus through the tentorial in~ cisure.
2. The impacted uncus forces [he' contralateral crus cerebri against the tentorial edge (Kernohan's notch) and puts pressure on the ipsilateral eN III and posterior cere~ bral artery. As a result. the folto}ving neurologic defects occur. a. Ipsilateral hemiparesis occurs'as a -result ofpressure on the' corticospinal tract.
which is located in the contralateral crus cerebri. b. A fi.'«ed and dilated pupil~ ptosis, and a "down~and-out" eye are caused by
pressure on the ipsilateral oculomotor nerve. c. Contralateral homonymous hemianopia is caused by compression of the pos~
terior cerebral artery, whi<;h_ irrigate~ the visual cortex. -
G. 'Papilledema (choked disk) is noniriflammatory congestion of the optic disk as a re~ sulr of increased intracranial pressure. It is most commonly caused by brain tumors. subdural hematoma, or hydrocephalus. It usually does not alter visual acuity, bur it may cause bilateral enlarged blind spots. It is often asymmetric and is greater on the side of the supratentorial lesion.
I. INTRODUCTION.)he autonomic nen'ous system (ANS) is a general visceral effen motor system that controls and regulates smooth muscle, cardiac muscle, and glands I A. The Ai'S consists of twO types of projection neurons:
I B. Autonomic output is controlled .by the hypothalamus.
C. The Al'S has three dhisions: '.
:1.. Sympathetic. Figure 18-1 shows the sympathetic innervation of the ANS.
2. Parasympathetic. Figure 18-2 shows the parasympathetic innelY;atio~ of the AN: I Table 18-1 compares the effects of sympathetic and parasympathetic activity c organ systems. . I
3. Enteric. The enteric division includes the intramural ganglia of the gastroimest nal cract, submucosal plexus, and myemeric plexus. .
II. CRANIAL NERVES (eN) WITH PARASYMPATHETIC COMPONENTS includ I the follo\ving:
I A. eN III (ciliary ganglion)
B. eN VII (pterygopalatine and-submandibular ganglia)
C. eN IX (otic ganglion)
D. eN X [temlinal (mural) ganglia]
III. COMMUNICATING RAMI of the ANS include:· -'
A. \Vhite communicating rami, which are found between T-l and L-3, are myelinated.
B. Gray communicating rami, which me found ~( :111 spinal lc'vcis, are unmyelinated. . /
IV. NEUROTRANSMITTERS of the ANS includl::
A. Acetylcholine, which is the neUfO!f;'msmittcr orthe preganglionic neurons
B. Norepinephrine, which is the neliTOrransminer of the postganglionic neurons, with the exception of swcnr glanJs nnt! some blood \'csscls that receive cholinergic sympa~hctic innervation
C. Dopamine, which is the neurocr:msmictn (l~ :he sinall ir\t{'nsclv i1\!()[(·.';CCl1t (SIr) cells, wllleh arc intcrncurons (If the ~.\·:li:':lti,(·,· '::,:\(,Ii.
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·.~~?;;~·:-S~~·~~?~:~>:·:; ~ ".:;' ~ ... -.. . ,
~ ....... . , ..... -: ..
A~tonomic Nervous System 99 . . •••••••••••••••••••••••••••••••• ~ ••••••••••••••••• a ••• ••••••••••••••••••••••••••• _ •••••••••••••••••••• _ ..................................... ~ ••••••••••••••••••••••••••••••••••••••••••••••••• 6 •••••••••••
en '0 c: co en iii Cll := en '0 c: co fI'i Cll 13 en :J E '5. '-0 (3 Cll '-'-co fI'i
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Superior cervical ganglion.
\ \ \ \
L-3
,
\ , \ Sympathetic trunk'
. . . .. __ - Tarsal muscle
.... ....... -: .... Lacrimal gland .
--------------------~
Inferior mese·~teric plexus
.~ ..
....... Eye: dilator of pupil
. Submandibular and sublingual glands·
.Parotid gland
Heart
Bronchial tree
Stomach
Small intestine
Large intestine
Ductus deferens
Figure :1.8-:1. The sympathetic {thoracolumhar} innervation of the autonomic ncrvous systcm. The entire sympathetic innervation of the hcaJ is through the superior cervici11 ganglion. Gray cOl11munic;\ting r;1mi arc found lit all ~rinal cord le\"(:ls. White communicating rami nrc (ound only in spinal segmcnts T-l through L-3.
. Constriction of pupil (miosis) Contraction for near vision Stimulation of secretion Watery secretion
InGrease in conduction velocity Increase ".
. Deceleration (vagal arr'est) Decrease in ·conduction velocity Decrease (atria)
Contraction' Relaxation Relaxation
Relaxation Contraction Decrease
Little or no effect Contraction Ejaculation * Secretion of epinephrine and
norepinephrine •
Gluconeogenesis and glycogenolysis .
lipolysis Renin release
'. . Contraction
Contraction Relaxation Increase
Contraction Relaxation Erection'"
• Note erection versus ejaculation: Remember point and shoot: p = parasympathetic. s = sympathetic. Reprinted with permission from Fix J: BRS Ne.uroanatomy. Media, PA, Williams & Wilkins, 1991.
D. Vasoactive intestinal polypeptide (VIP), a vasodilator Jhat is colocaljzed with acetylcholine in some postganglionic parasympathetic fibers
E. Nitric oxide (NO), a newly disco\'ered neurotrarysmitter that is responsible for the relaxation of smooth muscle. It is also responsible'for penile erection (see Chapter 22).
/ "
V. CLINICAL CORRELATION
A. Megacolon (Hirschspr~ng's diseas~, or congenital aganglionic megacolon) is charncteri:ed by extreme dilation and hypertrophy of the colon, with fecal retention, and by the nbsence of ganglion cells in the myenteric plexus. Ie occurs when neural crest cells do not migrate into the colon. .
B. F:llnilial dysautonomia (Riley-Day syndrome) predominantly nffccts Jewish childn:n. Ie is an autOsomal reccssivc Hait that is charactcrized by abnormal swcaring, un-
'~.
I zsmr ron ro=.'7u o RSS72rsCFIrmnw·
102 Chapter 18 I ...... , ................................................................ __ ............................................................................................................................... .
~tnhle blol,J·pr~s$ure (e.g., orthl,stntic hypo{ension),.Ji(ficll~ty in (~eding (as r.-rcH.lb I of inadequate- muscle tlme in rhe gnstrointestinal rrilcd. nnd progressive sensory 10:::' It results in the ,,-,SS of neurons it, the autonomic imd sensory ganglia. '
I c. Raynaud's disease is a painful disorder of the terminal, aneries of the extremities. It i: ch.-\racteri:ed 1:-)' idiopathic pnrl)xysmaI bilateral cy;mosis of the digits (as n result l'lf arterial an9 nrreri.olar cQnstr~crion bec~use'of cold or emotion). It mn}' be'treared by prt!- . gangli~nic s);mpathectomy.. . - . I
D. Peptic ulcer disease results (rom excessive production of hydrochloric acid because \..'\1
increased parasympathetic (tone) stimulation.
E. Horner's syndrome (see Chapter 17) is oculosympmhetic paralysis.
F. Shy-Drager syndrome itwoh"es preganglionic sympathetic neurons from the inter· mediolaternl cell column. It is characterized by orthostatic hypotension. anhidrosiS'. impotence: and bladder monici~·.
G. Botulism. The toxin of Clostriciiuln botulinum blocks the release of acetylcholine and results in paralysis of all striated muscles. Autonomic effects include dry eyes, dry mouth. and gastrointestinal ileus (bowel obstruction).
. H. Lambert-Eaton myasthenic syndrome (see Cl:apter 22)
I. INTRODUCTION . . ·A. General structur~ and function. The hypothalamus is a division of the diencephalon
that subsen'es three systems: the autonomic ner\'ous system, endocrine system, and limbic system. The hyporhalal1lUs helps to maintain homeostasis.
B. Major hypothalamic nuclei and their functions.
:1.. The medial preoptic nucleus (Figure 19-1) regulates the release of gonadotropic hormones from the adenohypophysis. It contains the sexually dimorphic nucleus, the de\"elopment of which depends on testosterone l.:n:ls.
2. The suprachiasmatic 'nucleus receh'es direct input from the retina. It plays a role in the regulation of circadian rhythms.
Paraventricular and supraoptic nuclei • regulate water balance • produce ADH and oxytocin • destruction causes diabetes insipidus • paraventricular nucleus projects to
autonomic n\lclei of brainstem and spinal cord
Anterior nucleus • thermal regulatibn
(dissipation of heat) • stimulates parasympathetic ,NS • destruction results in hyperthermia
Preoptic area' • contains sexual dimorphic nucleus • regulates release of gonadotropic
Figure 19-1. ~\'1aj(lr hypothalamic nuclei and their fUllctions. ADH :::: antidiuretic hormone; eN = cranial lIeJ\'c; DOPA = dopamine; NS = nervous system.
1.03
d'. rs ??'WtzUSN'7zsrrrcw'
:1.04 'Chapter 19 I
.................................................................................................................................................................................. ~ ........................ -. 3. The anterior nucleus pln)'s n role in tcn'ipermure regulation. It stilllul.ues tht' I
p;lr~ls)"mpathetk neryous system. Dcstfl.Jctilln results in hyperthermia.
4. The par.\\"entricularnudeus (Figure 19~2) synthesi:es antidiuretic hOnl\\.'nt' I (ADH), oxytocin, nndC()rticotrorin~rele .... sing' hormone, It gives rise to tht' suprnopticL)hYrllphy~eal tract, which proj~cts to the neurohypophys.is. It regulate~ water babllce (conser\,ation) nnd projects directly to the llutonomic nudei of the I brain seem and nil k\'e1,s of the spinal cord. D~struction resules in diabetes in~ slpidus, . .
5. The suprnoptic n·.1cleus synthesi:es ADH <lnd oxytocin (similar to the para\'entrieular nucleus), I
6. The dorsomedial nucleus. In an'imnls, su\'age behavior re'suIts when this nucleu~ is stimulated.
7. The ventromedial nucleus is considered a satiety. center. \\lhen·stimulated, it inhibits the urge to eat. Bilateral i:lestruccion results in hyperphagia, obesity, and sm'age beha\'ior,
Supraoptic nucleus
Superior hypophyseal artery
Anterior lobe (adenohypophysis)
Paiaventricular'nucleus
Third ventricle Arcuate. (tuberal) nucleus
Tuberohypophyseal tract .~
Supraoptifohypophyseal tract
Sinusoids of infundibular stem
Oxytocin ADH
Posterior,lobe (neurohypophysis)
.'
/Hypophyseal vein "
Inferior hypophyseal artery
Figure 19-2. The hypophyseal ponnl systcm.TI,c para,'cntricubr .md s\Jpraoptic nuclei produce nnticliurctic hormone (ADH) and oxytocin and lranspore them rhr0ugh the suprnopticoh),l'0physcal trace to [he cnpitJary I:<:d (I( the neurohypophysis. The nreuatc nucleus of thc infundibulum transports" ypor hOI lam ie-st irn u la [i ng horm()nf.:S dH(\ugh [he [uht:whYrophy~c:al traer to rhe SinU$tlids of die in(undib\lhr ::(:1\\. These si nu:;oid s the n d r;\ i [\ into die ;c'c"fHhry clpill:Jry ['\ext!' in (he ;1<kll(.fll'pol'hy.,is.
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. Hypothalamus ··105 ................................................................... .: .......................................... -................... _ ................ : ....................................................................................................... -8. The nrcuate (infundibular) nucl~us cOllmins neurons that produce fa~tors rh;,t
stimllhl£e or inhibit the action of the·h)'roth~ICltnus. This nucleus gh'es rise· to
the tul-erohn'oph\'$eal tmcc, which [crmin~tcs in the hypophysl!i11rortal system (see Figure 19-2) of the infundibulum (medium eminence). It cpnmins neurons that rroduce dl)pamine (i.C;., prolactin-inhibiting factor).
9. The mamillary nucleus.receh·es input from the hippocampal formation through the rostcommissural fornix. It projects to the anterior ilucleus· of the thalanllis through the mamillothal~mic .tract (pare of the Papez circuit). Patients with \X1ernicke's encephalopathy, which is a thiamine (\'itarnin B1) deficienc)" ha,-c lesions in the mamillary nucleus. Lesions are also assodated with alcoholism.
:10. The posterior hypothalamic nucleus plays a role in thermal regulation (Le., consen'ation ,1nd increased production of heac). Lesions result in poikilothermia (i.e., inaHlity to thermoregulate).
1.1.. 1l1e Iat~ral hypothala~ic nuc~eus induces eating when stimulated. Lesions cause anorexia and starvation. .
c. 1 .... 1ajor fiber systems of the hypothalamus
:1. The fornix is the largest projection to the hypothalamus. It rrojects from the hi!=,pocampal fortnation to the mam.ilIary nucleus, anterior nucleus of the thalamus. and septal area. The fornix then projects from the septal area to the hippocampal fonnation. .
2. The medial forebrain bundle cra\'erses the entire lateral hypothalamic area. It interconnects the orbitofrontal cortex, septal area, hypothalamus, and midbrain.
3. The rnamillothalamic tract projects from the mamillary nuclei to the anterior nucleus of the thalamus (part of the Papez circui.t)-
4. The stria terminalis is the major pathway fr9.rr\ the amygdala. It interconnects the septal area, hypothalamus, and amygdala.
5. The supraopticohypophysial tract conducts fibers from the supraoptic and para\Oencricuiar nuclei to the neurohrp~physis, which is the release she for ADH and oxytocin.
6. The tuberohypophysial (tuberoinfundibular) tract conducts fibers from the arcuate nucleus to the hypophyseal pomil system (see Figure 19-2).
7. The h ypothalamospinal tract contains direct descend ing ClDtOnOm ic fi bers. These fibers influence the preganglionic sympathetic neurons of the intennediolateral cell column and preganglionic neurons of the sacral parasympathetic nucleus. Interruption abo\'e the first thoracic segment (T-1) causes Homer's syndrome. .. .
II. FUNCTIONS
A. Autonomic function /'
:1. The anterior hypothalamus has nn exci[~tory effect on the rnrasympathetic ner-vous system.
2. The posterior hypoth:llamus ha~ an cxcitlltory effect on the sympathetic nervouS sys[(:m.
106 Chapter 19 .......................................................................................................... __ .................................................................................................... ~ ..... -2. Thl! posterior hypothalamus helps to produce nnd conserve henr~ Destruction
Ciluses the in;lbili~y tll thermoregular.e.
C. \Vater balance regulation. The paraventricular nucleus synthesizes ADH, which controls ",<'rer excrerion by (he kidneys.
D.' Food intake regulation. Two hypoth;'llamic nuclerplay.~ role in the control of appetite .
. 1.; When stimulated, the·,·entrom·ediaI nucle~s inhibits the urge to eat.'Bilnteral dc~ struction results in hyrerphagia. obesity. and savage behavior.
2. When stimulated, the lateral hypothalamic nucleus induces the urge to eat. Desmlction caU5es starvation and emaciation.
, .' III. CLINICAL CORRELATION
A. Diabetes insipidu·s, whicn is charaqeri:ed by 'polyuria and polydipsia. is the best known hyrothalamic syndrome. It results from lesions of the ADH pathways to the rosrerior lobe of the pituitary gland.
B. The syndrome of inappropriate ADH secretion is usually caused by lung rumors or drug tI-ierapy (e.g., carbama:epine, chlorpromazine). . .
c. Craniopharyngiom~ is a congenitaf tumor that originates from remnants of Rathke's pouch (see Chapter 4). This cumor'.is usually calcified. It is the most common surratentorial tumor in children and the most common cause of hypopiruitarism in children.
:1.. Pressure on the chiasma results in bitemporal hemianopia.
2. Pressure on the hypothalamus causes hypothalamic syndrome (i.e., adiposity, diabete.s iI)sipidus. disturbance of temperature.r~gulation, and somnolence).
D. Pituitary adenomas account for 15% of cliniCal symptomatic intracranial tumors. They are rarely seen in children. \YJhen pituitary adenomas are endocrine,acch·e, they cause endocrine abnorrnaliti~s (e.g., amenorrhea and galactorrhea f~.om a prolactin-secreting adenoma, the most common type). .
:1.. Pressure on the chiasma re?ults 'in bitemporal hemianopia.
2. Pressu're on the hypothaIam""s may cause hypothalamus syndrome . ..'
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20 Limbic .System
L INTRODUCTION. The lil'nbic S\·Hem is considered the anatomic· substrate that under~ lies beha.'"ioral and emotional exr~essiorl.lt js expressed thtough the hypothalamus by way of the autonomic nen'ous systern.
II. MAJOR COMPONENTS AND CONNECTIONS
A. The orbitofrontal cortex mediates the conscious pe.rception of smell. It has recipro~ cal connections with the mediodorsal nucleus of the thalamus. It is interconnected through the ·medial forebrain bundle .with the septal area and hypothalamic nuclei.
B. The mediodorsal nucleus of the thalamus has reciprocal connections with the or~ bitofrontal and prefrontal cortices as well as the hypothalamus. It receives input: from the amygdala and plays a role in affective behavior and memory.
C. The anterior nuCleus of the thalamus receives inpuc from the mamillary nucleus through the mamillothalamic tract and fornix. It ptojects to the cingulate gyrus and is a major link in the Papez circuit. . .
D. The septal area is a telencephalic structure. It has reciprocal connections with the hip~ pocampal formation through the fornix and with the hypothalamus through the me~ dial forebrain bundle. It projects through the stria medulIaris (thalami) to the h3.be~ nular nucleus.
E. The limbic lobe includes the subcallosal area, paraterminal gyrus, cingulate gyrus and isthmus, and parahippocampal gy}Us, which includes the uncus. It c<?ntains, buried in the parahippocampal gyrus, the hippocampal formation and amygdaloid nuclear com~ plex.
F. The hippocampal formation is a sheet of archicortex that is jelly~rolled into the parahippocampal gyrus. It functions in learning, m~mory, and recognition of no\·elty. It receives major input through the enrorhinal cortex· and ·projects major output through the fornix. Its major structures include the following:
1.. The dentate gyrus, which has a three~layered archicortex. It contains granule cells that receive hippocampal input and projecr/output to the pyramidal cells of the hippocampus and subiculum. .
2. The hippocampus (cornu Ammonis), which has a three~la)'ered archicortex. It contains pyramidal ~ells that proj~ct through the fornix to the septal area and hy~ pothalamus.
3. The subiculum, which receives input through the hippocampal pyramidal cells. It projects through the fornix to the mamillary nuclei and the nnterior nucleus ofehe rhnlnmus.
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I :108 Chapter 20 .......................................................................................................... : .............................. : .............................................. ~............... I
G •. The'nmygdak'id cO~llplex (amygdala) (Figure 20~ 1; see also Figure Z 1,1] is a b;lsal gat) glion chm: und~rlies the p.lmhiprocampal unclIs. In humans •. stimuhuion causes f~;, and signs M =,ymp;lthcdcll\·ernctivicy. In other anill1:1ls. stimulation results in cc~~;, I tion of nctiviry and height~ned atrenciwness. Lesions C:1use placidity nnd hypcrsexu;l l:-ch:,wior. . . . .
1. Input is fr~,in the' senSl't)' nssocitltion' cortices. olfact<;>ry bulb cmd conex, liYPl)' thalamus and septal mea. "nd hiplX"m~\IX\1 formatio.n. . . I
2. Output is through the stria terminalis to the hypotha'lamus and septal area. Ther( is also output [0 rhe mediodorsal nucleus of the thalamus. 1
H. The hypothalamus has reciprocal connections with the am}:gdala.
I. The limbic midbrain nuclei mid associated neu.rotransmitters include .the ventI:,,! I tegmental 'mea (dopamine). raphe nuclei (serotonin), and locus ceruleus (nore-F'i. nephrine).
III. THE PAPEZ CIRCUIT (Figure 20~2) includes the following limb.ic structures: I A. The hippocampal formation, which projects through the fornix to the mamillary nu-
cleus and serral area .
B. The mamillary nucleus
Hippocampal formation
Fomlx·~-·~·J :. " f
-: ~ - ' Stria terminalis
Septal area Hypothalamus ~------~ ~~----~--~
Diagonal band of Broca· - - _. - - -~-:
VAFP/VAPP, , .
" .
Olfactory bulb and olfactory cortex
P--~-+l Autonomic centers Amygdaloid nucleus') of brain stem
Sensory association .' and limbic cortices/
, , ,
VAFP/VAPP ,. .
•
Figure 20-1.. Major conneccions of the amygdnloiJ ill/cleus. TI,is nuclells recei\'cs input frorn three major sources: the olfactory system, semory llSsocimion and limbic cortices, and hyporhnlamus. M"jor output is through two ch'lImcls: the ~tria (erminalis projects to the hy!'l'th:llamu5 nnJ the septal area, and the ventral <l/nygdabfug,,1 p:Hhwny (VAFP) projects co the h)'pothalatnll~, brain stem. :md spinal corJ. A smaller e(ferent bundle, the diOl!,:(lIl:ll hand o( BrocOI, pr(ljccts co rhe sepral area. /\"(crcnr fihers (rom rhe hypo!h:il<lll)lIs ;lt1d br;lin seem en tn the :1Illn:ch1()je! l1ucleus through the '.'cntral ;ll1lYi;lhlppct;ll [1:1thl'(;l), (\1/\[>1').
Figure 20-2. 1\tajor atT'erenc ,md efferent limbi~ cc.nnections ,,"'If the 11irpocampal f\."'ImlatiC'!\. TIl is (ormation has. three c\."'ImponentS: the hi~~rocalllpu:, (cornu Am.monis \. :,ut-iculum ... m.:l .:lemme gyru~. TIle hip!=,ocampus rr\"'\ject:S to the seFc".l.uea. the suc-iculum projects to the mamillary nuclei. and the dencace gyrus does not project beyond the hirr.xamral t"onnatk1 n. TI,e cir~ cuit of Pare: follows this route: hirrocampal (OnllatiOn co mamill8.0· nucleus to anterior thalamic nucleus to
cingulate gyrus to emorhinal cortex to hiprocampal formation.
c. The anterior thalamic nucleus
Anterior nucleus of thalamus
!--------AnteriOr limb of . internal capsule
Cingulate gyrus
t ----------Cingulum
Entomirial cortex ..
f -. ---~ ---. Perforant pathway
Hippocampal formation
!,
D. The cingulate gyrus (Brodmann's areas 23 and 24)
E. Ihe'entorhinal area CBrodmann's are~ 28)
IV. CLINICAL CORRELATION
, ~ --- ,----- Fornix
A. Kli.iver-Buc), syndrome results .. from bilateral ablation of the anterior temporal lobes, including the amygdaloid nuclei. It causes psychic blindness (visual agnosia), hyper' phagia, docility (placid.ity), and hypersexuality.
B. Amnestic {confabulatory} syndrome results from bilateral infarction of the ,hippocampal formation (Le., hippocampal branches of th,e posterior cerebral arteries and anterior choroidal arteries of the internal carotid arteries). It causes anterograde am
. nesia (Le., inability to learn and retain new information). Memory loss suggests hip .. pocampal pathology. " ,
C. Foster Kennedy syndrome results from m~ingioma of the olfactory groove. The meningioma compresses the olfactory tract and optic nerve. IpSilateral anosmia and optic atrophy and contralateral pap,illedema occur as a result of incrensed intracranial pressure.
D. The hippocampus is the most epileptogenic pan of the cerebrum. Lesions may cause psychomocor attncks. Sommer's sector is very sensitive to ischemia,
E. Bilateral transection of the (ornix may cause the acute amnestic syndrome (Le., inability to consoliJme short'term memory into long-term memory).
Figure 20-3. Midsagittal section through the brain stetn and diencephalon showing the distri1:>ution of lesions in \Vemicke's encephalopathy. (A) ~ lediodorsal nucleus of the thalamus. (8) Massa incennedia. (C) Peri\'entricular area. (D) Mamillary nuclei. ~E) Midbrain and pontine tegmentum. (F) Inferior coIli<;ulus. Lesions in the mamillary nuclei are associated with \Vemicke's encephalopathy and thiamine (vitamin B1) deficiency.
F. \Vernicke's encephalopathy results from a thiamine (vitamin B1) deficiency. The clinical triad includes ocular disturbances and nystagmus, gait ataxia, and mental dysfunction. Pathologic features include mamillary nuclei, MD nuclei of the thalamus, and periaqueductal gray and pontine tegmentU1}l.~Figure 20-3).
G. Strachan's syndrome results (rom high-dose thfa'mine (vitamin B1) therapy. 111e clinical triad includes spinal a(a~.ia, optic atrophy, and nerve deafness.
H. Bilateral destruction or removal of the cingulate gyri causes loss of initiative and inhibition as well as dulling of the emotions. Memory is unaffected. Lesions of the anterior cingulate gyri cause placidity. Cingulectomy is used to 'treat severe anxiety and depression.
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2~ Basal Ganglia and Striatal Motor Syste-m
I. BASAL GANGLIA (Figure 21,1)
A. Components
:1.. Caudate nucleus
Corpus callosum
Lateral ventricle
Caudate nucleus
Thalamus -nR~~~~~~
Internal capsule
Claustrum
Third
Optic tract
Substantia nigra Mamillary body
Fornix
putamen} Globus Lentiform
pallidus nucleus
+-""",,,;;.,p..;.;.:.;,;...:,.......:;,.- Ins ul a
Subthalamic nucleus
Lateral ventricle
Figure 21.,1.. Coronal section through the midehalalllus He the level of the mamillar}' bodies. The basal gangli" me "II prominent at this le~'el ~lOd include the striatum and lentiform nucleus. The :illbthnlCllnic nucleus anJ suh:-.wntia nigra arc import"IH components of the~tri;lt,,1 IHn(()r svstCIll. Cl\t. = centwtneJian nuclemj VA = ventral anrerior nucleusj VL = \'cntrallatcrnl nuclells.
sa .rrr; '1W 'E" .,PXsWM'?zC"S?Hwfpwt¥CR'sannn
I 1.:1.2 Chapter 21 ............................... ;.~ ... ;:.~=.~~:.~ ....... :.......................................................................................................................................... I
3~ Globus pnllidus
B. Grouping of the basal gangli~
1. The striatum consists ,-'If the caudate nucleus nnd putamen.
2. The lentiform nucleus consists of the globus pallidus an'd putamen.
3. The corpus striattim consists of rhe lentiform nucleus and caud;-t'te nucleus.
4. The claustrum lies l:-etween the lentifonn nucleus and the insular cortex. I t has reciprocal connections between the sensory corrices (i.e., visual cortex).
II. THE STRIATAl:- (EXTRAPYRAMIDAL) MOTOR SYSTEM (see. Figure 21-1) plays a role in the initia~ion nnd execution of somatic motor nctivity, especi~l1y willed movememo It is also im'oh'ed in auromatic,stereotyped postural and retlex motor acth'ity (e.g., normal subjects swing their anns when they walk).
A. Structure. The :miaral motor system includes the foHowing structures:
i. Neocortex
2. Striatum (caudatoputamen, or neostriatum:) . .'
3. Globus pallidus
I I T
VA. VL eM
Thalamus
J. J. T
Subthalamic -nucleus ~
Neocortex
...... ,: ..... .
I ,. Globus paUidus
•
I - Substantia nigra
"
/ Brain stem and
spinal cord
Figure 2:1.-2. ;., lajm afferent and effcrent conncction; of the striatal systcm. The striatum receivcs In;-ljor in· put from Ihrcc :,\\urccs: the thaL"l\lIs, ncocortex, ;mJ .... !,,;., .. ,;., lIigl ••. Till: ~lfiatlll\\ projects to the globus pal. lidus and ~uh~tanti;\ nigra. TIlc globus p"lIiJus is thc effector nuclcus of the striatal systcm; it projects to the thalamw; and suhth.tI<llIlic nucleus. The ~lIhst:H1tia nigra also projects to the th;d;)mu~. The striatal motor system is exrrcs~ed rhn'lI!.:h rhe corricohllll';)f ;1Ilt! cortico.'r,in:ll tracts. ("':I\j c,i1trnll1c,li:1Il nucleus; GADA o=: -y;)~J)in()I'lltyric: ;l(i-i; V/\ =, \":!lU;t! ;ulterior J)lIclr:lI~; VI. c. "c·:lf'.': '-"" .. , .. : .. -
5. Substantia nigra (i.~ .• pars compacrn :lIld ~~ars rericularis)
·6. Thalamus (\·entml.'m~ril.)r, \'cmmllateml, and centromedian nuclei)
B. Figure 21-2 shows the major afferent and efferent connections of rhe striatal system.
C. Neurotransmitters (Figure 21-3) ~ .
III. CLINICAL CORRELATION
A. Parkinson's disease is a degenerati"e disease that affects the substantia nigra and its projections to [he striatum.
1.. Results. Parkinson's disease cau~es a depletion of dopamine in the· substantia nigra and striatum as well as a loss of melanin-containing dopaminergic neurons in . the substantia nigra. .
2. Clinical signs are Fradykinesia: srooped posture, shuffling gait, cogwheel rigidity, ,pill-rolling tremor, and masked facies. Lewy bodies are found in the melanincontaining neurons of the· substantia nigra. Progressive supranuclear palsy is associated with Parkinson disease.
. 3. Treatment has been successful with L-Dopa. 'Surgical inten'entlon includes pallidotomy (rigidity) and \'entral t?alomotomy (tremor).
Thalamus
GLU Neocortex
GLU Brain stem and 1-----_1 spinal cord
1 ~ // (Destruc.~~p·n results in Huntington's disease)
~ ~ \ ~ sg ./ \ , " .. - - - ~ (Lesions found here
in Wilson's disease) .. , nucleus
GJ.obus pallidus
GABA '-----.--...,',.....,
(Destruction results in hemiballism)
.
, (lesions found h~fe
in kernicterus),
Figure 2:1-3. M,lj(lr neurmransmicters of the srriacnl motor systelll. \Vithin the srriaCllIl1, globus pallidus, and pars rcticularis (.\f the ~lIbSt01ntia nigra (5. nigra), -y·aminohutyric aciJ (GADA) is the predominant neurotransminer. GABA may c(lcxist in the samc neuron with enkerhalin (ENK) or slIhswncc P (SP). Dopaminecontaining nellWn5 arc fi.lllnJ in the pars compacta of the substantia nigra. Acetylcholine (ACh) is found in the )(}Cal circuit nCliWIlS oi the MriaCllm. Thc subthalnmic nuck-lls projects excit:Hl'ry glllt:lminergic fibers to the globus palliJlIs. GLU = gllltamate.
B. Methylph~n)·ltetrahyJropyriJine·(MPTP)-irtduced parkinsonism. MPTP is nn anakll-! I of mc!~~ridine (Dc!lll~n.\l)"lt destrors dop:lInin~rgic neurons in ,the subscmlcia nigm. ~
C. Huntington's diseas~ {chorC!'l)i~ .'10 inherited autosomal dominant movement dis-ord~r that is traced tl) .. l single gene Je£ect 01\ chromosome -to I :1.. Ie is associated with degeneration of the cholinergic and y-aminobutyric acid
(GABA)-ergic neurons of the striatum. It is'accompanied by gyml mrophy ill the I fronml and temrl..'\t"".lliobes. . .
2. Glutamate excitotoxicity. GLU is released in the strintum and'binds tO,its recercors on srrinml neurons resulting in an action rotenral. OLU is removed from the extra- I cellular space by astTocytes. In Huntington's disease OLU is bound to the N-methylO-asrartate (N~lDA) recertorresulting in nn influx of cakium ions and subsequent cell de.ath. This cascade of e\'ents with neuronal death most likely occurs in'cere~ < I bro\'ascular accidents (e.g., stroke).
:1.. Sydenham's chorea (St. Vitus' dance) is the most common cause of chorea overall. It occurs primarily in girls, typically after a' bout of rheumatic fever. ' H.
I I
2. Chorea gravidarum usually occu,rs during the second trimester of pregnancy. Many patients have a history of Sydenham's chorea.
E. Hemiballism is a movement disorder that usually resuh:s from a vascular lesion of the subthalamic nucleus. Clinical signs include violent contralateral flinging {ballistic} movements of one or both e'xtremities.
F. Hepatolenticular degeneration {\Vilson's disease} is an autosomal recessive disorder that is caused by a defect in the metabolism of c·opper. The gene locus is on chromosome 13. /. .
:1.. Clinical signs include choreiform or athetotic mqvements, rigidity, and wing-beating tremor. Tremor is (he most common neurologiC sign. .....
2. Lesions are found in the lentiform nucleus. Copper depQsition in the limbus of the cornea gi\'es rise to the corneal Kayser-Fleischer ring, which is a pathognomonic·sign. Deposition of copF'er in the liver leads to multilob~r cirrhosis.
3. Psychiatric symptoms include psychosis, personality disorders, and dementia.
. 4. The diagnosis is base'd on low ::erull1 ceruloplasmin, ele\'ated urinary excretion of co}:,per, and increased copper cLw\cenu(ltion in a Ihoer biopsy specimen.
S. Treatment includes penicillamine. a chelator~ .. .':'
G. Tardive dyskinesia is a syndrome l1( repetitive choreic movement that affect the face and trunk. It results from treatment with phen9thi:lZines, blir.yrophenones, or meta-c1opramidc, ,,/
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22 Neurotransmitters
I. IMPORTANT TRANSMITTERS AND THEIR PATHWAYS
A. Acetylcholine is the l"najor transmit:t-~r of th~ peripheral ne~\'ous system, neuromuscular junction, parasympathetic nervous system, preganglionic sympathetic fibers, and postganglionic sympathetic fibers that inneryate sweat glands and some blood vessels in the ske letal muscles {Figure 22-1}. Acetylcholine is found in the neurons of the somatic and visceral motor' nuclei in the briin- steni and spinal cord. It is also found in the basal nucleus of Meynert; which degenerates in Alzheimer's disease.
B. Catecholamines. Figure 22-2 shows [he biosynrher.ic pathway for catecholamines. Epinephrine, although a catecholamine, plays an insignificant role" as a central nen'Ous system neurotransmitter. In the body, epinephrine is found primarily in the adrenal medulla. In the central nen'ous system, ic is restricted to small neuronal clusters in che brain stem (medulla),
1.. Dopamine (Figure 22-3) is deplered in pati~ncs with Parkinson's disease and increased in patients with schizophrenia. Dopainine is found in the arcuate nucleus of the hypothalamus. It is the prolactin-inhibiting factor. Its two major receptOrs are DI and D2•
Acetylcholine (ACh)
Nucleus basilis of Meynert in forebrain ~-~ (Alzheimer's disease)
Cranial nerve, motor neurons, and preganglionic parasympathetic neurons
Spinal motor neurons Autonomic preganglionic neuro'ns
Local circuit neurons in striatum (caudatoputamen)
Hippocampal formation
Figure 22-1. Dj~trjhutjon of acetylcholine-containing neurons and their ;lxona\ projections. The basal nucleus of Mcynert project!; to the entire cortex. This nuclells degenerates in patients with Alzheimcr's Jisease. Striatal acetylcholine local circuit neurons Jegcncratc in p;tticnts with HlIntington's disease.
Phenylethanofamine N-methyl transferase Figure 22-2. Synthesis of catecholamines from rhenrhllanine. Epinephrine, which is derh'ed from nc'repineFhril)e, is found primarily in the adrenal medulla.
Epinephrine
. - ..; -'
a. Dl receptors are postsynaptic. They activate adenylate cyclase and are exci-taton·.
b. D., r~ceptors are both postsynaptic and presynaptic. They inhibit adenylate q:Clase and are inhibirory. Antipsychotic drugs block D2 receptors.
I
I I I I I -I
I 1 I
2. N ore'pinephrine (Figure 22-4) is the transmitter of most postganglionic sympa- I therie neurons. Antidepressant drugs enhance its transmission. a. Norepinephrine plays a role in'anxiety states. Panic attacks are belie,-ed to re-
sult from paroxysmal discharges from the, locus ceruleus, where norepineph- I rinergic neurons are found in [he highesc'concemration. ~v10st postsynaptic receprors of the locus ceruleus pathway are /3 1 or /3z receprors that activate adenylate cyclase and are excitatory. -,' I
Figure 22-3. Distrihutioll o( dopamine-containing neurons anJ t".ir projectiolls. Two major nsecnding dopnminc pathways nrbe in the midhrnin: the nigro~lri.lIal trnct (rl111l the ~lIbs(;lntia nigra and thc Il1csolirnhie traer (rom the \'cntr~d tcglllcllt;d are:l, [n patients with Parkinson's disea>c, I\,~s of dOp'1fllillcrgic neurons occurs in the ,'\lb~r;lI1ria nij;r;, ;llld the \'(:l1tr;d t<:~:I11<:nt;d ;l/C;], 1\')p;lfI1incq;ic I1Cllr\)I~~ (rum ,he ~\[CU;\tc ll\lC!cUS of ,he
1 I' f - ,- ··1! -- - I I ' h\·t".Jth~·~l~jn)tl\ p:.\-!~._!··r ttl 1,\\: r'l;!r.d \'(')\tj~ (d r )~: \;\lt~lldi )l!!\il:~_ I .i\)~\':',i\'\(·i~:ic nCllrnn~ il1.)!O!r ~-'I;~),l::ti;1
Figure 22-4. Distributi,-'n ,-,f n,-'rerinerhrine-colltaining neurons and their projections. The k..,cus ceru!eu~ \ :-.'caced in che r~)ns and miJh.~in} is [he chief $(lurce of noradrenergic fibers. The locus ceruleus rrojeccs c,-"\ ;;;11 ;:- "rrs of the central ner\"ou~ :\'Hem.
b. 111.~ catecholamine hypothesis of mood disorders scates thac reduced noreFineFhrine acth'iry is related to depression. and that increased norepinephrine activiry is related to mania.
C. Serotonin [5,hydroxytryptamine (5-HT)] is an indolamine (Figure 22-5), Serotonincontaining neurons, are found only in the raphe nuclei of the brain stem,
i. The permissh'e serotonin hypothesis stat~s that when 5-HT activity is reduced, decreased le\'els of catecholamines cause-,depression and insomnia. In addition. when 5-HT activity is increased, elevated levels of catecholamines cause mania, Dysfunccion of 5-HT may underlie obsessive-compulsh'e disorder.
2. Certain antidepressants increase 5-HT availability by reducing its reuptake. 5-HT agonists that bind 5-HTI.A. and those that block 5-HT2 ha\'e antidepressant ~rorerties. Fluoxerine is a selective serotonin reuptake inhibitor (SSRl).
D. Opioid peptides (endogenous opiates) induce responses similar to those of heroin and morphine. '
i. Endorphins incluqe l3-endorphin, which is the major endorphin found in the brain. It: is one of the most powerful analgesics known (48 times more potent than morphine). Endorphins are found exclusivelr in [he hypothalamus.
.. .,' ";."
2. Enkephalins are the most widely distributed and abundant opiate peptides. They are found in the highest concentration in the globus pallidus. Enkephalins coexist with dopamine, ),-aminobutyric acid (GABA), norepinephrine, and acer:'Icholine. They arecolocalized inGAB~;_efgic pallidal neurons, and they playa role in pain suppression.
3. Dynorphins follow the oistribtftion map for cnkephalins.
E. Nonopioid neuropeptides
1.. Substance P plays a role in pain transmission. It is most highly concentrated in the substantia nigra. It is lllso found in the dorsal root ganglion cells and substantia gelatinosa. It is colocalizcJ with GABA in the striaronigr:11 tract and pbys a role in movement dIsorders. Substance P levels nrc reduced in patients with Huntington's disease.
Raphe nuclei in midbrain, pons, and medulla Tryptophan
+ Tryplophan-5-hydroxyJase
, 5·Hydroxytryptophan
+ .Aromatic L-amino acid decarboxylase
Serotoniri (5~Hydroxytryptamine) '.
Figure 22-5. Distritution of j.hydroxytryptamine (seroronin).containing neurons and their projections. Serotonin'comaining neurons are found in the nuclei of the raphe. They project widely to the forebrain. cere·
,bellum. and spinal cord. The inset shows the synthetic pathway of serotonin.
2. Somatostatin (somatotropin-release inhibiting factor), Somatostatinergic neu· rons from the anterior hypothalamus project,c.heir axons to the median eminence, where somatostatin enters the hypophyseal portal system and regulates the release' of growth honnone and thyroid-stimulating honnone. The concentration of somatostatin in the neocortex and hippocampus is significantly reauced in patients with Alzheimer's disease. Striaml somacosra~in levels are increased in patients with Huntington's disease.
F. Amino acid transmitters
1.. Inhibitory amino acid transmitters " a. GABA (Figure 22·6) is the major inhibitory neurotransmitter of the brain. Pur·
kinje, stellate, basket, and GoJgi cells of rhe cerebellar cortex are GABA-ergic. (1.) GABA,ergic striatal neurons project (0 rhe globulus pallidus and sub-
stantia nigra. , .' . (2) GABA~ergic pallidal neurons project to "the thalamus. (3) GABA,ergic nigral neurons project ,to the thal;lInus. (4) GABA receptors (GABA-A :md ,GABA.B) are intim(l[ely associated
with bemodiazcpinc·binding sitci'Bemodimepines enhance GABA ac· , -tivir}'. (a) GABA-A receptor:; open chloride channels. (b) GABA,B receptorS ;ue found on the terminals of neurons that usc
another transminrr(Le., nor('rin('rh!'!!~e, dopnmine, serotonin). Activntion of GAllA·B receptors decreases (he release of the other transmitrer.
b. Glycine is the m:ljor inhibi{~)ry nClirorr:lmmiHcr of! he spin:'!! cord. I ( is used hv th(: fZen')h;)w cells of thf:!,iln! corel.
Figure 22-6. DistributiL'll1 ot' -y-aminobutyric acid (GABA)-containing neurons and their projections. GABA-ergic neurons me the maj0r inhibitory cells of the central nervous system. GABA local circuit neuron~ are found in the neocortex. hipF0.::ampal formation. and cerebellar cortex (Purkinje cells), Striatal GABA~ergic neurons project (0 the 'thalamus and subthalamic nucleus {not sho\\·n}.
2. Excitatory amino acid transmitters
. Glutamate
a. Glutamate (Figure 22~7) is the major excitatory transmitter of the brain. Neocortical gluramatergic neurons project to the striatum, subthalamic nucleus. and thalamus. (:1) Glutamate is the transmitter of the cerebellar granule cells. (2) Glutamate is also the transmitt:er'of nonnociceptive, large, primary af
ferent fibers that enter the spinal cord and brain stem. (3) Glutamate is the transmitter of the corticobulbar and corticospinal
tracts .
Pyramidal neurons of neocortex
Cortieostriatal fibers --f-----\ Fornix
-"---"<-~' Pyramidal cell of . hippocampal formation
~-=~~ Granule cells of Septal nuclei cerebellar cortex
Cortieobulbar and corticospinal tracts--~..l "~A"\'O'
Proprioceptive fibers in dorsal roots
Figure 22-7. Disniblltion o( glutamate,containing neurons and their pr·ojections. Gllltamate is the major c;o;ciwtory transmitter of rhe central nervous sysrcm. Cllrricalghumn<lccrgic neurons projecr to the striatum. Hippocampal and 5uhiclll"r glutumatcrgic neurons project through th!: fornix to the septal arca and hypothalamus. The ~ranule cdls o( the cerehellllrn arc ~llItam<lrcrgic.
b. A~part:lte. 'llll.tjl'r excit:1{I.'ry transmitter of the bmin. is the transmitter of the:
climbing hl--ers l~f the ,erd't;lIl1lll. Neurons of climbing fibers are fopnd il1,[h\! . inferh..)f l,li\'at), nudell$.
c. Beha\'ior.ll corrdation .. GIUt:lllli1te, through. its N-methyl-D-a5parrare (NMDA) receptors. plays a rule in .Iong-term potentiation (n memory process) ~'f hip~:~ampal n~·uron~ .. otlltnmatc plays n .role in kindling and sub'sequent sei:ure ncti\'ity. Under certain conditions. glutamate and its analogs are neurotoxic. '.. .
d. Glutamate excirotoxicity. GLU is re1ensed in the striatum nnd binds ro its receptors t,)t\ $triaml n~urot\s resulting in an action potential. GLU 'is removed from the extracelluhlr space by asrrocyres. In Huntington's disease GLU i~ bound to the N-methyl-D-aspartate (NMDA) receptor resulting in nn influx
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. of calcium ions.and subsequent cell death. This cascade of events with neu-· .1 ronal demh most Iik~lr occurs in cerebrovascular accidents (stroke). . .-
3: Nitric 'oxide is a rece'ntly discQ\'e.red gaseous neurotransmitter thai: is' produced when nitric oxide,syntha~econ\'erts arginine to citrulline. a. It is located in the olfactory system, striarum, neocortex, hippocamral forma
tion. supraoptic nucleus of the hypothalamus, and cerebellum" b. -Nitric oxide is resronsible for smooth Il!uscle relaxation of the corpus ca\'er
nosum and thus renile erection. It is also· believed to playa role in memory formation because of its long-tenn potentiation in the hippocampal formation. In addition. nitric oxide functions as a nitrovasodilator in the cardio-vascular system.
II. FUNCTIONAL AND CLINICAL CONSIDERATIONS
A. Parkinson's disease results from degeneration of the dopaminergic neurons that are round in the pars compacta of the substantia nigra,. It causes a reduction of dopamine iIl the striatum and substantia nigra (see Chapt~:~ 21 III A).
B. Huntington's disease {chorea} results from a loss of acetylcholine- and GABA~ containing neurons in the suiatum (caudatoputamen). The effect is a loss of GABA in the striatu'm and substantia nigra (see Chapter 21 III C). <
C. Alzheimer's disease'result:; from the degeneration of cortical neurons and cholinergic neurons in the basal nucleus of Meynert. It is associated with a 60% to 90% loss of choline acetyluansferase in the c,erebral cortex. Histologically, Al::~eimer's disease is characterized by the presence of neurofibrillary tangles, senile (neuritic) plaques,
. amyloid substance, granulovacuolar degeneration, and Hirano bodies.
D. ~1yasthenia gravis results (rom autoantibodies against the nicotinic acetylcholine receptor on skeletal muscle. These ant:bodies block the postganglionic acetylcholine binding site. Thymic cells augment B-ccll producdon of autoantibodies. The cardinal manifestation is fatigable weakness of the skeletal muscle. The extraocular muscles, including the levator palpebrae, are usually invoh'.ed. Edrophonium or neostigmine in~ jection is used (or diagnosis. .
/ E. Lambert,Eaton myasthenic syndrome is CC1\JSCJ by n prcsynaptic defect of acetyl-
choline release. It causes weakness in the limb muscles, but not the bulbar muscles. Fifty percent of cases are associated :with neoplasms (i.e., lung, brc<1st, prostatc). In these paticnts, muscle strength imprm'cs wirh lISC. ]n contrast, in patients with my3sthenia gn\\'is, muscle usc results in muscle fatiguc, and autonomic dysfunction includes Jry mouth. constipation, impotcnce, and urinary incontinence.
I. INTRODUCTION. TIle cerebral cortex. the thin. gray co\'ering of both hemispheres of the brain. has two tYr~s: the neocortex (90%) a~d [he allocortex (10%). Motor cortex is the thi~kest (4.5 mm): visual cortex is the thinest (1.5 mm).
II. THE SIX-LAYERED NEOCORTEX. Layers II and IV of the neocortex ar~ mainly afferent (i.e., receidng). Layers V and VI are mainl); efferent (i.e., sending),
A. Layer I is the molecular layer.
B. Layer II is the external granular layer.
C. Laye~ III is the external pyramidal layer. Ie gives rise to association and commissural fibers and is the major source of corricocortical fibers.
D. Layer IV is the internal granular layer. It receives thalamocortical fibers from the thalamic nuclei of the ventral tier (i.e., ventral posterolateral and ventral posreromedial). In the visual cortex (Brodmann's area 17-),',layer IV receh'es input from the lat-eral geniculate body. '".
E. Layer V is the internal pyramidal layer. It gh'es rise to corricobulbar. corticospinal. and corticostriatal fibers. It comains the giant pyramidal cells ofBeq, which are found only in the mowr cortex (Brodmann's.are'a 4), .
F. Layer VI is the multiform layer. It is the major source of corticothalamic fibers. It gi\'es rise to projection, commissural, and association fibers.
./ III. FUNCTIONAL AREAS (Figure 23-1)
A. Frontal lobe
i. The motor cortex (Brodmann's area 4) and premotor cortex (Brodmann's area 6) are somalOtopically organized (Figure 23-2). Destruction of these areas of the frontal lobe causes contralateral spastic paresis, Contralateral pronator drift is associated with frontal lobe lesions of the cor~,icospinal tract.
2. Frontal eye field (Brodmann's area 8). Des'truction causes deviation of the eyes to
the ipsilateral side. ,/
3. Broca's speech area (Brodmanll's areas 44 and 45) is located in the posteribr part of the inferior frontal, gyrus in the dominant hemisphere (Figure 23-3). Destruction results in expressivc, nonfluent aphasia (Broca's aphasia). The patient understands both writcen and spoken Iangu:lge, but cannot articulate spcech or write normally. Broc"a's aphasia is lIsually associated with contrnlaternl facial and arm wcakness bccause of the in\,oh·cmcnc of the motor strip.
4. Prefrontal cortex (f3rodmann's areas 9-12 anJ 46-47). Destruction of the ante-
·'1 I .......................................................................................................... : ............................................................................................ " ..... .
A
Primary motor cortex ,(4) . ' . \
\
Frontal eye field (a) ,
Broca's speech area of left hemisphere (44, 45)
B
Secondary somatosensory ;' and gustatory cortex,
I Primary auditory cortex (41, 42) I
Prefrontal cortex (9, 10, 11,12)"
Primary motor cortex (4h \ \
Septal area"''''
limbic lobe I I I I
Primary olfactory cortex (34)
, , ,
I.
. . ,Primary somatosensory cortex (3, 1, 2)
I
,
\
" ",Vestibular cortex (2) '"
..;, Visual association J cortex (39, 19, 18)
- Primary visual cortex (17)
'Auditory association cortex (Wernicke's speech area of left hemisphere) (22)
I Primary somatosensory cortex (3, 1, 2) I .
• " / Somatosensory association
I cortex (5, 7) I
- Limbic lobe
?' Visuarassociation cortex (19, 18)
"Uncus (28) .:~ Primary visual cortex (17)
, ParahipP:>campal gyrus
/
Figure 23-1. Some motor ;and semory areas of the cerebral corcex. (A) lmeral com'ex surface of the hemisphere. (B) ~1edial surt:lCC of the hemisphere. The nllinbcr~ refer (0 the Brodmann brain map (I3rodrnann's areas).
Figure 23-2. The sensory and motor homunculi. (A) Sensory representation in [he postcentral gyrus. (8) ~lotor representation in the precentral gyrus. (Reprinted with permission from Penfield W, Rasmussen T: The Cerebral Coreex o{l'dan. New York, Hafner, 1968, pp. 44, 57.)
rior two~thirds of the frontal lobe conv.exity results in deficits in concentration, orientation, abstracting ability, judgm~nt, and problem-solving ability. Other frontal lobe deficits include loss of initiative, inappropriate behavior, release of sucking and grasping reflexes, gait apraxia, and sphincteric,. incom:inence .. Destruction of tb:! orbital (frontal) lobe results in inappropriate social behavior (e.g., use of obscene language, urinat'ing in public). Perseveration is associated with frontal lobe lesions.
B. Parietal lobe
:1.. The sensory cortex (Brodmann's areas 3, I, and 2) is somacotopically organized (see Figure 23-1); Destruction results in contralateral hemihypesthesia and astereognosis.
2. The superior parietal lobule (Brodmann;s areas 5 and 7). Destruction results in contralateral astereognosis and sensory neglect.
3. The inferior parietal lobule of the donlinant hemIsphere. Damage results in Gerstmann's syndrome, which includ~s"the following deficits: a." Right and left confusion ,-b. Finger agnosia . c. Dysgraphia and dyslexia d. Dyscalculia " e. Contralateral hemianopia or lower quadrantanopia
4. The inferior parietal lobule of the nondominant hemisphere. Destruction results in the following deficits: a. TopogrClphlc memory loss
Figure 23-3. Cortical areas of the dominant hemisphere that play ~n important role in language production. The \'isu~,l image! of a word is projected from the \'isual cortex (Brodm:mns area 17) to the visual association cortices (Brodmann's areas 18 and 19) and then to the angular gyrus (Brodmann's area 39), Furtherprocessing occurs in \\1emicke's speech area (Brodmann's area 22), \\:here the auditory form of the word is recalled, Through the arcuate fasciculus, this information reaches Broca's speech area (Brodmann's areas 44 and 45), where moror sFeech Frograms control the \'ocali:ation mechanisms of the precentral gyrus. Lesions of Broca's speech area, \Vemicke's sFeech area, or the arcuate fasciculus result in dysphasia, ,
b. Anosognosia c. Construction apraxia (Figure 23·4) d. Dressing apra.,<ia e. COI.1tralateraI sensory neglect f. Contralateral hemianopia or lower -quadrantanopia ,,"
C. Temporal lobe
", '
+- ,
/
A B. C
Figure 23-4. Testing (or construction apraxia. (A) TIle patient was askcJ (0 copy the (ace 0(" clock. (8) The paticnt was a!'>kcd to bisect a horiwll(:11 linc, (C) TIle patient W;JS llskeJ to copy a cross. Tllcse drawings ~h(lw contr;dareral neglect. The rc.\ponsih1c lesion is (OUI10 in the nondOlllill;mt (righe) p;Hiecnl lobe. A left IWlT1i;lI1()pia, hy itself. docs not re~ult in C(IIHLlhceral !!t'!:l--cr_
Figure 23-6. Functions of the split brain afcer minseccion of the corpus callosum. Tactile and visual percepti .. 'n is projected w the contralateral hemisrhere, olfaction is perceived on the S<1me side, and audition is perc<!ived predominancly in the opposite hemisphere. 1l1e left (L) hemisphere is dominant (or language. The right (R) hemisphere i$ dominant for spatial construction and nonverb:l! ideation. (Reprinted with permission from :\"'t-ack CR. Demarest R): The HI/man Nen'ollS System. Malvern. PAt L~a & Febigcr. 1991, p. 416.)
, ,.-' ,"0'"
1. The primary auditory cortex (Brodmann's areas 41 and .12). Unilateral destruction results in slight loss of hearing. BilateraL loss results in cortical deafness. . /
2. \Vemickc's speech area i~ th~ dominant h{misphere is found in the posterior l-~art of the superior temporal g)'rus (Brodmnnn's aren 22). Dcstruction resulcs in receptive, fluent aphasia (Wernicke's aphaSia), in which the pmicnt cannot understand any form of bnguage. Spcech is sponrancous, fluent, and rnpid, but makes littl~ sensc.
3. Meyer's loop (sec Chapter 17 II F 2) consists of the visual radiations that project to the inferior o;)nk of the cnlc;)rine sulcus. Interrupt ion Cluses COn t r;) Ia rer;) I up!~cr qu"Jrant:mopi" ("pic in the sky").
su.lt:s in ipsilmt'ral nn.,)s\l,ia. An.irrimtivc lesion (psychomotor epilepsy). of the .un-cus r~slllts in ,-,If'lct\)ry anJ gustnrory hallucinations. . a. Olfactory groove men"ingionms comrress the 'olfactory tract and bulb result
ing in nn'-':Hnia. See Fos~c!r Kennedy syndrome Chapter 13 I C, b. Esthesioneuroblastom.l$ (olfactory neurobl"stomas) arise from bipolar sen
sory cells \-"If the (llfacrory mucosn; they can extend through the cribriform plate imo the at"lterk"lr crn"nial' fossa. Presenting symptoms are similar to Foster Kennedy syndrome ..
5. Hippocampal cortex -(archicortex). Bilateral lesions result in the inabiiiry to consolidate shorr-teml memory into long~term memory. Earlier memories a're retrievable.
6. The anterior temporal lobe, including the amygdaloid nucleus. Bilateral damage resulrs in Klii\"er~Bucy syndrome, which consists of psychic blindness (visual ag
-nosia), hyperphagia, docility, and hypersexuality.
7. Inf.eromedial occipitotempo'ral cortex. Bilareral.lesions result in the in.ability to
recogni:e once~{al1liliar faces (prosopagnosia). . . D. Occipital lobe. Bilateral lesions cause cortical blindness. Unilateral lesions cause con
tralateral hemianopia or quadrantanopia.
IV. FOCAL DESTRUCTIVE HEMISPHERIC LESIONS AND SYMPTOMS. Fig~re 23-5A shows the symptoms of lesions in. the -dominant hemisphere. Figure 23-5B shows the symptoms or lesions in the nondominam hemisphere.
V. CEREBRAL DOMINANCE is determined by the Wada test. Sodium amobarbital (Amy tal} is injected into the carotid artery: If the patient becomes aphasic, the anesthetic was adminiscered to the dominant hemisphere.'
A. The dominant hemisphere is usually the left he~isphere. It is responsible for propositional language (grammar, syntax, and semantics), speech, and calculation.
B. The non dominant hemisphere is usually the right hemisphere. It is responsible for three-dimensional, or spatial, perception and nonverbal ideation. It also allows supe-rior recognition of faces. . ....
. ,"
Figure 23-7. Chimeric (hybrid) figure of n f~ce used to examine the hemispheric function of COlll
missurotomized patienrs. The patient is" instructed to
fixate on [he Jot nnd is asked to describe what he sees. If he says that he sees [he fnce of a man, then the left hemisphere predominates in vocal tasks. Ifhe is nskcJ to point to the fnce nnd he points to the womnn, then the right hemisphere predominates in pointing tasks.
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1.28 Chapter 23 ......................................................................................................................................... , ..................................................................... . VI. SPLIT-BRAIN SYNDROME (Figure 23-6) is a discon~ection syndrome ihm. results
(rom transection of .the corpus .callosum. .
A. The dominant hemisphere is better :It vocal naming. .
B., The ~oridominant, mute hemisphere is bener at pointing to a stimulus. A person can, not name objects thm are presented to the nondominant visual c-ortex. A blindfolded person carmot n'ame' objects that are presented to the nondominant sensory ~ortex through touc.h.
C. Test (Figure 23-7). A subject views a composite picture of two half·,faces (Le., a chimeric. or hybrid. figure). The right side shows a man; the left side shows a woman, The picture is remO\·ed. and the subject is asked to describe what he saw. He may respond that he saw a man, but when asked to point to ,,,hat he sa~) he points to the
, .. . woman.
D. In a patient who has alexia in the.left visual field,.the verbal symbols seen in the right Yisual cortex have no access to the' language centers of the left hemisphere,
VII. OTHER LESIONS OF THE CORPUS CALLOSUM
A. Anterior corpus callosum lesion may result in ~kinetic mutism or tactile anomia.
B. Posterior corpus callosum (splenium) lesion may result In alexia'without: agraphia,
C. Callosotomy has been successfully-used to treat "drop attacks" (colloid cyst of third \'entricle).
BRAIN AND SPINAL CORD TUMORS (see Chapter 5)
J I I I I I I I I I I I I I I I I I I I
I I
--,'
I ~
I I I I I I I I I I I I I I I I
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.24 Apraxia, Aphasi'a, and Oysprosody
I. APRAXIA is the inability to rerfonn·.motor acti\'ities in the 'presence of intact mot~r and' sensory systems and normal cl)n1rrehensh::m.
A. Ideomotor apraxia is the inal-ility, in response ro a \'erbal command, ro perfonn mo~ tor acti\'ity thm can ~e rerformed with ease spontaneously (e.g .• sticking oue the rongue). This condition is associated with a les;ion in the dominant hemisphere.
B. Ideational apraxia is the inal-ility to rerform a n1ulristep activity or demonstrate the use of a real object (e.g .. rool): This condition is associated with a lesion iri the dom~ inant hemisphere. .
C. Construction apra.'Xia is the inability to draw or construct a geometric figure (e.g .• the face of a clock). If the patient draws only the right half of the clock. this condition is called hemineglect. and the lesion is located in the right inferior parietal lobule (see Figure 23~4). .
D. Gait apraxia is the inability to use the lower li~bs properly. The patient has difficulty in lifting his feet from the floor. a frontal lobe sign seen with normal pressure hydro~ cephalus (gait apraxia, dementia, incontinance) .
• II. APHASIA is impaired or absent communication by speech, writing, or signs .(Le., loss
of the capacity for spoken language). The lesions are located in the dominant hemi~ sphere. Associate the following symptoms and lesion sites with the appropriate aphasia (Figure 24~1).
A. Broca's (motor) aphasia
:L Lesion in frontal lobe. in the inferior frontal gyrus (Brodmann 44.45)
2. Good comprehension
3. Efforrfu I speech ,
4. Dysarthric speech
5. Telegraphic speech / , 6. Nonfluent speech
7. Poor repetition
8. Contralnrerallower facial and upper limb weakness
B. \Vcrnicke's (sensory) aphasia
1. Lesion in posterior tempor:lllobe. in rhe superior temporal gyrus (Brodmann 22)
Figure 24-:1.. ll1e "aphasia square" makes it easy to differentiate the six most common "national board" aphasias. Broca's, conduction, and Wernicke's aphasias are all characterized by poor repetition. (Adapted with rermission from Miller], Fountain N: Neurology Recall. Balrimore, \Villiams & \Vilkins, 1997, p. 35.)
3. Fluent 5I='eech
4. Poor reI='eririon
5. Quadrantanopia
6. Paraphasic errors
a. Non sequiturs (L. does not follow) are statements irrelevant to the question asked. .
b. Neologisms are words with no meaning. c. Driveling speech
C. Conduction aphasia
1.. Transection of the arcuate fasciculus; the arcuate (asciCLI Ius interconnects Brod-mann's speech area with \Vernicke's spee~.9/~rcn.
G. Global aphasia results from a lesion of the-perisylvian area, which contains Broca's and Wernicke's areas. Global aphasia combines all of the symptoms of Broca's and \Ver- . nicke's aphasias. : . .
H. Thalamic aphasia is a dominant thalamic syndrome. It closely resembles a thought disorder of patients with schizophrenia and chronic drug-induced psychosis. Symp.tOms include t1uent paraphasic speech with nonnal comprehension and repetition. . .
I. Basal ganglia. Diseases of the basal ganglia may cause aphasia. Lesions of the anterior basal ganglia result in nontluent aphasia. Lesions of the posterior basal ganglia result in fluent aphasia.
J. \Vatershed infarcts are areas of infarction in the boundary :ones of the anterior, middle, and posterior cerebral arteries. These areas are vulnerable to hypoperfusion and thus may separate Broca's and Wernicke's speech areas from the surrounding cortex. These infarcts cause the motor, mixed, and sens<;>ry transcortical aphasias.
III. DYSPROSODY is a nondominanr hemispheric language deficit that serves propositional language. Emotionality, inflection, melody, emphasis, and gesturing are affected.
A. Expressive dysprosody results from a lesion that corre~ponds to Bros:a's area, but is located in the nondominant hemisphere, Patients cannot express emotion or inflection in their speech.
. B. Receptive dysprosody results from a lesion that corresponds to \V'ernicke's area, but is located in the nondominant hemisphere. Patients cannot comprehend the emotionalityor inflection in the speech they hear.
/ ,.
I I I I I I I I I I I I I I I I I
Cranial Nerve
I-::-Olfactory
II-Optlc
II/-Oculomotor Parasympathetic
Motor
IV-Trochlear
V-Trigeminal Motor
Sensory
VI-Abducent
type.
SVA
SSA
GVE
GSE
GSE
SVE
GSA
GSE
'. Appenc;fix: Table o(Cranial Nerves
Origin
Bipolar olfactory neurons' (in olfactory ~pithelium in roof of nasal cavity)
Retinal ganglion cells
Edinger·Westphal . nucleus (rostral midbrain)
Oculomotor nucleus (rostral midbrain)
Trochlear nucleus (caudal midbrain)
Motor nucleus CN V (mid pons)
Trigeminal ganglion and mesencephalic nucleus CN V (rostral pons and midbrain)
f!1uscles of mastication and tensor tympani muscle
Tactile, pain, and thermal sensation from the face; the oral and nasal cavities; and the· supratentorial dura
Lateral rectus muscle
Course
Central axons project to the olfactory bulb via the cribriform plate of the ethmoid bone.
Central axons con-verge at the' optic disk and form the optic nerve, ...... hich enters the skull via the optiq canal. Optic nerve axons terminate in the lateral geniculate bodies.
Axons exit the midbrain in the interpeduncular fossa, traverse the cavernous sinus, and enter the orbit via the superior orbital fissure.
. Axons decussate in superior medullary velum, exit dorsally inferior to the inferior colliculi, encircle the midbrain, traverse the cavernous sinus, and enter the orbit via the superior orbital fissure.
Ophthalmic nerve exits via the superior orbital fissure; ·maxillary nerve exits via the foramen rotundum; mandibular nerve exits via the foramen ovale; ophthalmic and maxillary nerves traverse the cavernous sinus; GSA fibers enter the spinal trigeminal tract of eN V.
Axons exit the pons from the inferior pontine sulcus, traverse the cavernous sinus, and enter the orbit via the superior orbital fissure.
Viscera of the thoracic and abdominal cavities to the left colic flexure (via terminal (mural) ganglia]
Muscles of the larynx and pharynx
Tactile sensation to the external ear
Mucous membranes of the pharynx, larynx, esophagus, trachea, and thoracic and abdominal viscera to the left colic flexure
Taste from the epiglottis
Intrinsic muscles of th~·.larynx (except the cricothyroid muscle) via recurrent laryngeal ne·rve
Sternocleidomastoid and trapezius muscles
Intrinsic and extrinsic muscles of the tongue (except the palatoglossus muscle)
Course
Axons exit (motor) and enter (sensory) medulla fr9m the. postolivary sulcus; axons exit and enter the skull via the jugular for& men; GSA fibers enter the spinal trigeminal tract of CN V; GVA and SVA fibers enter .the sotitary tract.
Axons from the cranial division exit the medulla from the postolivary sulcus and join the vagal nerve; axons from spinal division exit t:-,~ spinal cord, ascend through the foramen magnum, and exit the sKull via the jugular foramen_
Axons exit from the preolivary sulcus of the medulla and exit the skull via the hypoglossal canal.
SVA = special visceral afferent; SSA = special somatic afferent: GVE/= general visceral efferent; GSE = general somatic efferent: SVE = special visceral efferent; GSA = general somatic afferent; GVA = general visceral afferent;-CN = cranial nerve.
lwlic page numb$!rs Je$ignatl! tlgurl:!:': p.1gs: I\llll\b~rs folkm'ed by "t': designate cables; (see also) refers to relate topics or more demiled c\'"'\pic ~reilkdl.)\\"n~, Tl'pics h,l\"ing more than one subentry nre listed under the noun [e,g BoJy (bodies): carociJ]" - _
Abducent nerve (CN \'1) (see linda Cr.mial nerves) .Acce~sory nerye (CN Xl) (see IInd.:r Cranial nen'es) Accommodation, ocular. 66-67' --Acetylcholine. 98, 113-. 115 Acoustic neuron)a (5chw,mn0111a). 33. 34. 60,
cuneate. of medulla, 39 dentate, 86, 89 globus Fallidus, 111-111 gracile, of medulla, 39 of inferior colliculus. 1 hYFOthalamic, 116 lentitonn, III mamillary, 6, IC8 (see also Body; mamillary) niger. III olivary
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