NeuroanatomyBy

Dr.Faris Al-Haddad

M.B.Ch.B, PhD AnatomyCollege of Medicine,

Hawler Medical UniversityArbil, Iraq

e-mail: farisurgeon@gmail.com

Introduction

The Nervous System is conventionally divided into three major parts:

1.1. Central nervous system (CNS), Central nervous system (CNS), 2.2. Peripheral nervous system (PNS)Peripheral nervous system (PNS)3.3. Autonomic nervous system (ANS)Autonomic nervous system (ANS) The three component parts act in concert in the

overall control and integration of the motor, sensory, and behavioral activities of the organism.

The methodologic creativity and observational acumen of anatomists, physiologists, psycholo-gists, and physicians have been impressive & rewarding, but their work is far from finished.

(Functional Neuroanatomy: Text and Atlas, 2nd ed)

Adel K. Afifi M.D., M.S. Ronald A. Bergman Ph.D.

Central Nervous SystemCentral Nervous System

1.Brain: Consists of:

• ForebrainForebrain Cerebrum Diencephalon• MidbrainMidbrain• HindbrainHindbrain Medulla Oblangata Pons Cerebellum

2. Spinal Cord: Consists of:

1.1. Cervical segment Cervical segment

2.2. Thoracic Segment Thoracic Segment

3.3. Lumbar segmentLumbar segment

4.4. Sacral segmentSacral segment

5.5. Coccygeal segmentCoccygeal segment

Peripheral Nervous SystemPeripheral Nervous System

PNS Consist of :PNS Consist of :• Cranial nerves (12 pairs) • spinal nerves (31 pairs) and their associated ganglia, that include:

1.Cervical spinal nerves (8)

2.Thoracic spinal nerves (12)3.Lumbar spinal nerves (5)4.Sacral spinal nerves (5)5.Coccygeal spinal nerves (1)

Autonomic Nervous System

The autonomic nervous system (ANS) is the part of the nervous system concerned with the innervation of involuntary structuresinnervation of involuntary structures, such as:

• Heart• smooth muscles• glands.

It is distributed throughout the central and peripheral nervous systems.

The ANS is divided into The ANS is divided into two parts:two parts:

1.1. SympatheticSympathetic (Thoracolumbar)

2.2. ParasympatheticParasympathetic (Craniosacral)

In both parts, there areIn both parts, there are::• Afferent nerve fibers• Efferent nerve fibers. • Preganglionic fibers • Postganglionic fibers

3.3. Enteric divisionEnteric division (Myenteric & Submucosal Plexuses)

Theses ganglia from up downwards:1.Ciliary ganglion 2. Pterygopalatine ganglion3. Submandibular ganglion 4. Otic ganglion

Continuous red = pregang. Sympathetic fibersDotted red = postganglionic Sympathetic fibersCotinuous blue = preganglionic parasympathetic fibersDotted blue = postganglionic parasympatheticfibers

Continuous red = preganglionic. Sympathetic fibersDotted red = postganglionic Sympathetic fibersCotinuous blue = preganglionic parasympathetic fibersDotted blue = postganglionic parasympatheticfibers

Functions:Functions:

1. Sympathetic activity prepare the body for an emergency.

2. Parasympathetic activity are aimed at conserving and restoring energy.

3. It has been suggested that while the enteric plexuses can coordinate the activities of the gut wall, the parasympathetic and sympathetic inputs modulate these activities.

Vertebral canal

The vertebral canal Smooth-walled tubular, space formed by series of vertebral foramina lying one above the other, ends in sacral canal.

• Anteriorly Anteriorly :1. Bodies of the vertebrae, 2. Intervertebral discs,3. Post. longitudinal ligament.• Posteriorly:Posteriorly:1. Vertebral laminae, 2. Ligamenta flava,• At the sides:At the sides:1. Pedicles of the vertebrae 2. Intervertebral foramina.

Vertebral Canal contains:Vertebral Canal contains:

1.spinal meninges 2. spinal cord with its nerve

roots and their vessles.3.epidural space (extradural space) which contains:• loose connective tissue, • fat• Veins (Internal vertebral

venous plexus “IVVP” )

Internal Vertebral Venous Plexus (IVVP)Internal Vertebral Venous Plexus (IVVP)• its throughout the canal • Divided into :1.1. Two anterior plexeses:Two anterior plexeses: • Two longitudenal channels• Lie on deep surface of vertebral bodies• On sides of posterior longitudenal ligament.2. Two posterior plexeses:Two posterior plexeses:• Two longitudenal channels• Lie on deep surface of Laminae and ligamenta flava

• Both anterior and posterior IVVPs are united together by the Transverse PlexesTransverse Plexes opposite the laminae

• IVVPs receives the Basivertebral veinsBasivertebral veins, which are large veins

draining the draining the active red marrow in the bodies of the

vertebrae

• The IVVPs connected through intervertebral foraminae with the body wall veins :

1.1. Vertebral veins, Vertebral veins, 2.2. Posterior intercostal Posterior intercostal

veins, veins, 3.3. Lumbar veinsLumbar veins4.4. Lateral sacral veinsLateral sacral veins

Clinical points about IVVPs:Clinical points about IVVPs:• provides a venous bypass of the diaphragmvenous bypass of the diaphragm. It

functions when the inferior vena cava cannot cope with a sudden flush of blood resulting from a sudden increase of intra-abdominal pressure (e.g. in coughing or abdominal straining), Thus pelvic and abdominal venous blood is moment-arily squirted up the plexus above diaphragm, into posterior intercostal veins, and thereby into the superior vena cava.

• Thus its implicated in the spread of some pelvic spread of some pelvic tumorstumors e.g. of the prostate to vertebral bodies, and even to the skull without tumors having to pass through the lungs.

Spinal Meninges

Meninges of Spinal Cord:• Three membranous layers of

connective tissue that protects spinal cord.

• Damage or infection meninges, such as in meningitis, can cause serious neurological damage and even death.

• Consisting of :1. Dura mater (outer)2. Arachnoid mater (intermediate)3. Pia mater (inner)

A.P i a M a t e r:

has 2 layers:

• Intima Pia (Inner Intima Pia (Inner Membranous LayerMembranous Layer):):

• Is intimately adherent to the surface of the spinal cord

• It is prolonged over the spinal nerve roots until where the dura blends blends with the epineuriumwith the epineurium of the mixed spinal nerves.

2.2. Epipia (Outer Vascular Layer)• Carries blood vessels that

supply and drain the spinal cord.

• Supports spinal cord by: A. Denticulate LigamentDenticulate Ligament : : Flat bands attaches to dura by 21 bands B. Filum terminale:Filum terminale: A filament fuses conus medullaris to the end of dural sac.

B. A r a ch n o i d

M a t e r • Delicate impermeable

membrane • Lies between pia and

dura• Send many delicate

processes across the subarachnoid space

to the pia mater, forming a lace-like arrangement.

Subdural space is a very narrow

(microscopic) space.

Subarachnoid spaceis a wide which is

filled with CSF

C. D u r a M a t e r

• A dense, strong, fibrous membrane• Encloses the spinal cord and cauda equina

Level Of Foramen Magnum:

• Attached firmly at the margin of foramen magnum.• Continues with the meningeal layer of dura of brain.

In Vertebral Canal (V.C.):

• Lies loosely in the V.C., Separated from its walls by the extradural space.

• Extends down to the level of the S1 and S2

• Below the site of spinal cord termination (conus medullaris), forms a sac filled with CSF.

• Spinal Dura: also ensheathes:1. dorsal roots 2. ventral roots, 3. dorsal root ganglia,4. proximal portions of spinal nerves, • Spinal dura then continues with the epineurium of spinal nerves at level of the intervertebral foramen.

Lumbar puncture • Needle is inserted

between the spines of L3-L4 or L4-L5 vertebrae

• Then penetrates the dura to subarachnoid CSF that is sampled.

• Since the spinal cord ends at the level of L1 vertebra, so there is no danger

Spinal anaesthesia• the anaesthetic

solution is injected into the subarach-noid space

• Also in space between L3-L4 or L4-L5

Epidural anaesthesia the solution is

injected at • any level into the

epidural (extradural) space

• without penetrating the dura,

• solution infiltrates through the meningeal sheaths containing the nerve roots

Spinal Cord

Definition: The thick, whitish cord of

nerve tissue (a part of CNS) that extends from the medulla oblongata down through the vertebral column and from which the spinal nerves branch off, that convey motor and sensory impulses to and from various parts of the body.

Gross Appearance of the Spinal Cord

LOCATION:• Begins/ At foramen magnumforamen magnum in the skull where it continues with medulla oblongatamedulla oblongata

IN ADULTS Spinal cord ends at:

1.1. As becomes conus medull- As becomes conus medull- arisaris at the level of the disc disc between L1 - L2 bodiesbetween L1 - L2 bodies.

2. A level little above elbowabove elbow, when arm by the side.

3. At Transpyloric Transpyloric level

• Thus, spinal cord lies in upper 2/3 of the vertebral upper 2/3 of the vertebral canalcanal

• At birth & young child, it is longer & usually ends

at the lower border of L2 or upper border of the L3upper border of the L3

Spinal Cord Shape:• Roughly CylindericalCylinderical• Cervical Enlargement Cervical Enlargement (C5- T1) due to giving origin to Brachial

Plexus.• Lumbar Enlargement Lumbar Enlargement (L2- S3) due to giving origin to

Lumbosacral Plexus.• Bottum called Conus MedullarisConus Medullaris • Filum terminaleFilum terminale is prolongation of

pia mater, attaches Conus to back of coccyx.

• Cauda equinaCauda equina is lumbosacral roots around the filum terminale.

Along the entire length of the spinal cord, 31 pairs 31 pairs of spinalof spinal nervesnerves are attached to it by:

1. Anterior (Motor) roots2. Posterior (Sensory) roots

• Each root is attached to the cord by a series of rootlets that extend along whole length of spinal cord segment.

• Each posterior root have a posterior root ganglion

External Features Of Spinal Cord

External Features thatunderlie pia mater are

1.1. Ventral (Anterior) Ventral (Anterior) Median FissureMedian Fissure : :

• its deep• underlies the

anterior spinal artery

2.2. Dorsal (Posterior) Dorsal (Posterior)

Median Sulcus:Median Sulcus:• Its shallow• Continuous with

dorsal median septum

3. Ventrolateral Sulcus:3. Ventrolateral Sulcus:• Shallow• Ventral rootlets emerge here

4. 4. DorsolateralSulcus:DorsolateralSulcus:• ShallowShallow• Dorsal rootlets Dorsal rootlets enter hereenter here

5.5. Dorsal Intermediate Dorsal Intermediate Sulcus:Sulcus:

• Shallow grooveShallow groove• Continuous with dorsal Continuous with dorsal

intermediate septum intermediate septum • Between dorsal lateral & Between dorsal lateral &

dorsal median sulcidorsal median sulci• Separates fasciculus Separates fasciculus

gracilis from fasciculus gracilis from fasciculus cuneatuscuneatus

Internal Features:Internal Features: In transverse section

consists of :

1. Gray Matter 2. White Matter

Gray Matter • As in other regions of

C.N.S, the gray matter of the spinal cord consists of a mixture of :

1. Nerve cells (Neurons) and their processes,

2. Neuroglia, 3. Blood vessels.

Gray Matter of Spinal Cord• H-shaped in cross section.

Consist of : 1. Anterior gray columnAnterior gray column2. Posterior gray columnPosterior gray column3. Gray commissureGray commissure : : containing the small central canal, it unites both above columns. 4. Lateral gray columnLateral gray column : : is present in thoracic & upper lumbar seg- ments of the cord.

• Amount of gray matter present at any level of spinal cord is related to amount of muscle innervated.

• Thus, its size is greatest within the cervical and lumbosacral enlargements of the cord, which inner-vate the muscles of the upper and lower limbs, respectively.

A. Nerve Cell Groups in

Anterior Gray Columns:

1. Medial group: • present in most

segments• innervating

skeletal muscles of the neck and trunk.

2. Central group:• smallest group• present in some cervical

and lumbosacral segments.• In C3-5, some neurons

innervate the diaphragm and are referred to as: phrenic nucleus.

• In C1-C6, some of cells innervate trapezius and sternocleidomastoid muscles and are called : accessory nucleus. The axons of these cells form the spinal part of the accessory nerve.

3.Lateral group: • present in the

cervical and lumbosacral segments of the cord

• responsible for innervating the skeletal muscles of the upper and lower limbs respectively.

ANT. GRAY HORN CELLS

GROUP MEDIAL CENTRAL LATERAL

LOCATION ALL SEGMENTSSOME CERVICAL &

LUMBOSACRALSEGMENTS

CERVICAL & LUMBOSACRAL

SEGMENTS

TARGET SKELETAL Ms.OF NECK & TRUNK

DIAPHRAGM,TRAPEZIUS,

&SCM

SKELETAL Ms. OF UPPER & LOWER

LIMBS

OTHERS / PHRENIC N,SP. ACCESSORY N. /

SUMMARY………..

B. Nerve Cell Groups in the Posterior Gray Columns

• Substantia gelatinosa group: • At apex of posterior gray column • Present in all Levels of the spinal

cord. • receives afferent fibers from posterior posterior

rootroot concerned with:

a. pain, b. temperature, c. touch

• Receive descending fibers from supraspinal levelssupraspinal levels.

2. Nucleus proprius:• situated anterior to the

substantia gelatinosa• In all levels of spinal cord.• receives fibers from the

posterior white columnposterior white column that are associated with:

senses of position and movement (proprioception), two-point discrimination, and vibration.

3. Nucleus dorsalis (Clarke's column)

• situated at the base of posterior gray column

• extending from the C8-L3 ( L4).

• associated with proprio-ceptive endings (neuro-muscular spindles and tendon spindles).

4. Visceral afferent nucleus

• situated lateral to the nucleus dorsalis;

• it extends from the T1- L3 of the spinal cord.

• It is associated with receiving visceral afferent information.

POST. GRAY HORN CELLS

NUCLEUS Substantia gelatinosa

Nucleus proprius

Nucleus dorsalis (Clarke's column)

Visceral afferent nucleus

LOCATION All All C8-L3 ( L4) T1- L3

RECIEVESSENSTION OF

1. pain, 2. temperature3. touch 4. Some

descending tracts

1. Position & movement (proprioception),

2. two point discrimination

3. vibration.

N.M. spindles

and tendon

spindles

visceral afferent

information

SUMMARY………..

3. Nerve Cell Groups in the

Lateral Gray Columns

• The intermediolateral group of cells • Cells are small • T1-L3 (L4): give rise to

preganglionic sympathetic fibers.

• S2-S4 : give rise to preganglionic parasymp-athetic fibers

4. Gray Commissure & Central Canal

• Connecting anterior & posterior gray horns

• In the center of the gray commissure is situated the central canal.

• The part posterior to the central canal is often referred to as the posterior posterior gray commissuregray commissure;

• But that anterior to the canal is called the anterior gray anterior gray commissurecommissure.

Central canal:• Throughout spinal segments• Superiorly, it is continuous

with cavity of the fourth ventricle.

• Inferiorly in the conus medullaris,

1. it expands into the fusiform shaped (terminal ventricle) 2. It is filled with cerebrospinal fluid. • Thus, the central canal is

closed inferiorly and opens superiorly into the fourth ventricle.

Rexed Laminae

• The cytoarchitecture of various sizes or shapes of neurons led Rexed to propose another class-fication based on 10 layers (laminae).

• its useful as it is related more to function

Blood Supply of Spinal Cord

A. Arteries of Spinal Cord

three small arteries:1. Two posterior spinal

arteries 2. Anterior spinal artery.3. Segmental spinal arteries

1. Posterior Spinal Arteries• The posterior spinal arteries

arise either: a. directly from: vertebral arteries inside the skull b. indirectly from the: posterior inferior cerebellar arteries.

• The posterior spinal arteries

supply the posterior 1/3 of the spinal cord.

2. Anterior Spinal Artery

• Formed by the union of two arteries, each of which arises from the vertebral artery inside the skull.

• Runs within the anterior median fissure.

• Branches from it supply supply anterior 2/3anterior 2/3 of the spinal cord.

3.Segmental Spinal Arteare branches of arteries outside the

vertebral column :1. deep cervical arteries,2. Intercostal arteries, 3. lumbar arteries.

• each segmental spinal artery gives rise to anterior and posterior radicular arteriesradicular arteries that accompany the anterior and posterior nerve roots to the spinal cord.

great anterior medullary artery of Adamkiewicz,

• One large and important artery• arises from the aorta in the

lower thoracic or upper lumbar vertebral levels;

• Unilateral, • In majority, enters the spinal

cord from the left side. • The importance of this artery

lies in the fact that it may be the major source of blood to the lower 2/3 of the spinal

cord.

Veins of the Spinal Cord• The veins of the spinal cord

drain into tortuous longitu-dinal channels that comm-unicate :

• Superiorly: In the skull with the veins of the brain and the venous sinuses.

• Inferiorly: They drain mainly into the Internal vertebral venous plexus.