Download MBBS Nerve Lecture PPT

Oculomotor nerve

? C N III
? Components - motor ( GSE , GVE )

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? Nuclei > Main oculomotor nucleus ( GSE )
> Edinger Westphal nucleus (accessory occulomotor nucleus ) ? GVE

? Functions -

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raises upper eyelid ( levator palpabrae superioris),
turns eyeball upward ( superior rectus , inferior oblique )
downward ( inferior rectus )
medially ( medial rectus ) .
constricts pupil ( constrictor pupillae muscle in iris ),

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accomodates eye ( constrictor pupillae , ciliary muscle , medial rectus )

? Opening in skull - superior orbital fissure
Nuclei of CN III and their connections
Main oculomotor nucleus

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? Is situated in - anterior part of gray matter that surrounds cerebral aqueduct of

midbrain .

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? It lies at the level of the superior colliculus.
? The nucleus consists of groups of nerve cells that supply all the extrinsic muscles of

the eye except the superior oblique and the lateral rectus.

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? The outgoing nerve fibers pass anteriorly through red nucleus and emerge on

anterior surface of the midbrain in interpeduncular fossa.

? The main oculomotor nucleus receives corticonuclear fibers from both cerebral

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hemispheres.

? lt receives tectobulbar fibers from superior colliculus and, through this route,

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receives information from visual cortex.

? It also receives fibers from medial longitudinal fasciculus, by which it is connected

to the nuclei of the fourth, sixth, and eighth cranial nerves.

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Edinger Westphal Nucleus

? Accessory parasympathetic nucleus

? Is situated posterior to the main oculomotor nucleus .

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? The axons of nerve cells, which are preganglionic, accompany other oculomotor

fibers to the orbit.

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? Here, they synapse in the ciliary ganglion, and postganglionic fibers pass through

the short ciliary nerves to the constrictor pupillae of the iris and the ciliary muscles.

? Receives

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> corticonuclear fibers for the accommodation reflex and
> fibers from pretectal nucleus for direct and consensual light reflexes.
Optic pathway and visual reflexes
Neural pathways of pupillary light reflex (left) and accommodation reflex (right).
Oculomotor Nerve Course

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? The oculomotor nerve emerges on the anterior surface of the midbrain .
? lt passes forward between the posterior cerebral and the superior cerebellar

arteries.

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? It then continues into the middle cranial fossa in the lateral wall of the cavernous

sinus.

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? Here, it divides into a superior and an inferior ramus, which enter the orbital cavity

through the superior orbital fissure.

? The oculomotor nerve supplies the following extrinsic muscles of the eye:

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levator palpebrae superioris,

superior rectus,

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medial rectus,

inferior rectus, and inferior oblique.
? It also supplies, through its branch to the ciliary ganglion and the short ciliary

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nerves, parasympathetic nerve fibers to the following intrinsic muscles:

constrictor pupillae of the iris

ciliary muscles.

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? Therefore, the oculomotor nerve is entirely motor and is responsible for

lifting the upper eyelid;

turning eye upward, downward, and medially;

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constricting pupil and accommodating the eye.

CS through brain at level of cavernous sinus

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Structures passing through superior orbital fissure and optic canal
Distribution of occulomotor nerve
Simplified summary of actions of extraocular muscles.
Trochlear nerve

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? C N IV

? Components - motor ( GSE ) ? Trochlear nucleus

? Supplies - superior oblique muscle

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? Function - assists in turning eyeball downward and laterally ,
intorsion of the eyeball

? Opening in skull - superior orbital fissure

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Trochlear Nerve Nucleus

? Is situated in anterior part of gray matter that surrounds cerebral aqueduct of the

midbrain.

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? It lies inferior to oculomotor nucleus at level of the inferior colliculus.

? The nerve fibers, after leaving the nucleus, pass posteriorly around the central gray

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matter to reach the posterior surface of the midbrain.

? The trochlear nucleus receives corticonuclear fibers from both cerebral

hemispheres.

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? lt receives the tectobulbar fibers, which connect it to the visual cortex through the

superior colliculus .

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? It also receives fibers from the medial longitudinal fasciculus, by which it is

connected to the nuclei of the third, sixth, and eighth cranial nerves.

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Trochlear Nerve Course

? Is most slender of the cranial nerves .

? Is only CN which comes out through posterior surface of brainstem .

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? It emerges from midbrain and immediately decussates with nerve of opposite side.

? The trochlear nerve passes forward through the middle cranial fossa in the lateral

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wall of cavernous sinus .

? Enters the orbit through superior orbital fissure .

? The nerve supplies the superior oblique muscle of the eyeball.

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? The trochlear nerve is entirely motor

? It assists in turning the eye downward and laterally.

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CS through brain at level of cavernous sinus


Structures passing through superior orbital fissure and optic canal
CN IV Course and distribution

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Abducent nerve

? C N VI

? Components - motor ( GSE )

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? Supplies - lateral rectus muscle

? Function - turns eyeball laterally

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? Opening in skull - superior orbital fissure
Abducens Nerve Nucleus

? The small motor nucleus is situated beneath the floor of the upper part of the

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fourth ventricle, close to the midline and beneath the colliculus facialis .

? The nucleus receives afferent corticonuclear fibers from both cerebral hemispheres.
? It receives the tectobulbar tract from the superior colliculus, by which the visual

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cortex is connected to the nucleus.

? It also receives fibers from the medial longitudinal fasciculus, by which it is

connected to the nuclei of the third, fourth, and eighth cranial nerves.

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Abducens Nerve Course

? The fibers of the abducens nerve pass anteriorly through the pons and emerge in

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the groove between the lower border of the pons and the medulla oblongata .

? lt passes forward through the cavernous sinus, lying below and lateral to the

internal carotid artery.

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? The nerve then enters the orbit through the superior orbital fissure.
? The abducens nerve is entirely a motor nerve and supplies the lateral rectus muscle

and, therefore, is responsible for turning the eye laterally.

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