Cranial Nerves1

8/14/2019 Cranial Nerves1

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Cranial nerve nucleiCranial nerve nuclei


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1.general somatic afferent,GSA ( from skin)

2.general visceral afferent,GVA( from blood vessels,glands etc)

3.general somatic efferent,GSE(SE) (to skeletal muscles of

somitic origin)

Functional componentsFunctional components


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Functional componentsFunctional components

4.general visceral efferent,GVE(motor

fibres to smooth muscles and glands)

5.special somatic

afferent,SSA(vision,audition)

6.special visceral

afferent,SVA(taste)(smell)

7.special visceral efferent,SVE(all the

muscles derived from pharyngeal arches)


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Olfactory nerve(I)Olfactory nerve(I)


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Functional componentFunctional component

It has only one componentIt has only one component

SVA(special visceral afferent)SVA(special visceral afferent)


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Olfactory nerveOlfactory nerve

The olfactory system consists ofThe olfactory system consists of

the olfactory epithelium, bulb and tractthe olfactory epithelium, bulb and tract

olfactory areas of the brain collectivelyolfactory areas of the brain collectivelyknown as the rhinencephalon.known as the rhinencephalon.


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Olfactory bulb

I. Olfactory:

Sensorynerves forsmell

U
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The olfactory epithelium is located

in the roof, superior conchae, and

septum of the nasal cavity.


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Olfactory receptor cells arebipolar neurons

The olfactory bulb

is an enlargement of the rostral

end of the olfactory tract.


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the olfactory tract divides into

the lateral, intermediate, and

medial Striae


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Fibers from the pyriform cortex project to the

entorhinalcortex(Brodmann area 28),

which contains an olfactory association area thatsends projections to the hippocampus.

This portion of the limbic system is undoubtedly

associated

with the learning of likes&dislikes of foods.


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Olfactory projections


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TEST1.assessment of the patency of the

nostrils.

Each nostril is examined separately.The test involves occlusion of a single

nostril while the eyes of the patient are

closed.
http://www.eustatiantube.org/clinic/neuroexam/cranialmovies/odorants.asfhttp://www.eustatiantube.org/clinic/neuroexam/cranialmovies/odorants.asf


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The patient should inhale gently through

the open nostril in close proximity to a

common odorant

(e.g., vanilla, ground coffee, fresh

orange, etc.).The patient should be asked first whether

the odorant can be detected.

If detectable, the odorant should be

identified by name.


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If the patient fails at the task, the test

should be repeated with at least one

distinct odorant.

The test should be repeated for the

opposite nostril using entirely new

odorants.


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Optic nerve(II)Optic nerve(II)


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Functional component:Special somatic afferent(SSA)

Arises from the retina.Passes through the optic canals

to enter the cranial cavity and

decussates with its fellow

to form the optic chiasm.


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It then continues as optic tract

to reach Lateral geniculatebody and from here

it continues as optic radiation

to end in the visual cortex.


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Each optic nerve contains nasal andtemporal fibers.

The nasal fibers decussate in the chiasm

so that

each optic tract contains temporal fibers

of the same side

and nasal fibers of the opposite side.


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http://ect.downstate.edu/courseware/haonline/imgs/00000/3000/600/3612.jpg


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sphenoid

Arrows in optic canals


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The Visual Pathway from Below

Optic nerveOptic chiasmOptic tractLateral geniculate bodyOptic radiation

Visual cortexSuperior colliculus of themidbrainPutamenLong association bundle -inferior occipitofrontal fasciculus

Pulvinar of the thalamusCalcarine fissurePoster inferior horn of thelateral ventricle


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http://www.aph.org/cvi/brain_2.pdf


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Complete blind

hemianopia


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Various hemianopias


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The test is completed by askingthe patient to read a Snellen eye

chart viewed at 20 feet.


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Oculomotor nerve(III)Oculomotor nerve(III)


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Has a motor nucleus in the midbrain

(at superior colliculus)

which supplies all the extra ocular muscles

except

Lateral rectus and superior oblique.


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It also has a parasympathetic

nucleus(Edinger-westphal)

Which supplies sphincter pupillae

and ciliaris mucles.


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Functional components;

1.Somatic efferent.(SE)

2.General visceral

efferent(GVE)


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Course;

Passes through the mid brain to emerge

in the interpeduncular fossa.

Passes through the lateral wall of the cavernous sinus

Enters the orbit throughsuperior orbital fissures middle compartment.


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Divides into upper and lowerdivisions

Supply

Levator palpebrae

superioris,superior,inferior,medial recti

and inferior oblique muscles of theeye.


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Nucleus of III nerve

Ts of midbrain at the level of superior colliculus

Middle cranial fossa


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Arrow indicates cavernous sinus

Middle cranial fossa


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III

IV

V1

V2V3

Structures in the lateral wall of cavernous sinus


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The Cavernous Sinuses

A. Carotid Artery

B. TrochlearNerve

C. MaxillaryNerve

D. Abducens

Nerve

E. SphenoidSinus

F. Pituitary Gland

G. Cavernous

Sinus

H. OphthalmicNerve

I. OculomotorNerve


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Superior orbital fissure


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Bony orbit(RT) viewed from front


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Clinical aspects( ptosis)Clinical aspects( ptosis)


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Trochlear nerve (IV)Trochlear nerve (IV)


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Functional component:somatic efferent SE

Supply:superior oblique muscle of the eye

Nucleus:situated in the midbrain

at the level of inferior colliculus


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Its the only cranial nerve to emerge

from the dorsal aspect of the

brain stem(rest all emerge from the

ventral aspect).


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It is the only cranial nerve

that decussates with its fellow.


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Passes through the lateral wall of the

cavernous sinus

below the III nerve and above the

ophthalmic nerve.

Enters the orbit through the lateral part ofsup.orb.fissure.


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It then passes medially to supply

the superior oblique.


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Nucleus of IVnerve in the midbrainNucleus of IVnerve in the midbrain

(inferior collicular level)(inferior collicular level)

V

D


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IV nerve

Cavernous sinus


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Rt orbit(superior view)


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Damage to the

Trochlear nerve will

present as:

Extorsion (outward

rotation) of the affected

eye due to the unopposed

action of the inferior

oblique muscle.

.The patient will

compensate by moving

his head to intort the

contra lateral eye.


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Vertical diplopia (double vision)

due to the extorted eye.

Weakness of downward gaze mostnoticeable on medially-directed eye.

This is often reported as difficulty

in descending stairs.

What is torsion?What is torsion?


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What is torsion?What is torsion?

It is defined as rotation of an imaginaryIt is defined as rotation of an imaginary

point at 12o clock position on the cornealpoint at 12o clock position on the corneal

margin. If it moves externally(temporally) itmargin. If it moves externally(temporally) it

is called extorsion.is called extorsion. If it moves internally(nasally),it is calledIf it moves internally(nasally),it is called

intorsion.intorsion.


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Extorsion of the left eye(IVnerve palsy)


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Abducent nerve(VI)Abducent nerve(VI)


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Functional component:somatic efferent SE

Supplies lateral rectus only.

Nucleus: in the floor of the IV ventricle

deep to facial colliculus

Facial nerve fibers loop around this.


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Facial colliculus


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emerges at the interpeduncular

fossa in line with IIInerve.

Passes through the cavernous

sinus inferolateral to ICA.

Course:


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Enters the orbit through the

middle compartment,between the

two divisions of IIInerve and ends

by supplying lateral rectus.


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At the interpeduncular fossaIn the cranial cavity

VI


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III

III


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Showing the relationship withShowing the relationship with


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Showing the relationship withg p

circle of Willscircle of Wills

IIInerve

VI nerve


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Injury to Abducens nerve causes

the paralysis of ipsilateral lateral rectus.


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The eye is drawn medially due

to

unopposed action of medial

rectus.

This will result indiplopia(double vision)


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Strabismus the inability to direct both eyes to the same object.

Rt abducens palsy(no abduction)


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p y( )


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Testing of III,IV,VI nerves

III Oculomotor Eye movement

upward,

downward, and

inward; narrowing

(constriction) orwidening (dilation)

of the pupil in

response to

changes in light

The ability to move each eye

upward, downward, and inward

is tested by asking the person to

follow a target moved by the

examiner. The upper eyelid ischecked for drooping (ptosis).


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IV Trochlea

r

Eye

movement

downward

and inward

The ability to move

each eye downward

and inward is tested by

asking the person to

follow a target movedby the examiner.


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VI Abduc

ens

Side-to-

side

(lateral)eye

movement

The ability to move

each eye outward

beyond the midlineis tested.

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Cranial Nerves1

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