3rd, 4th and 6th cranial nerve

3rd, 4th and 6th CRANIAL NERVE

BY DR. SUNITA KUMAWAT Deptt. Of PHTHALMOLOGY Sardar Patel Medical College, BIKANER

Oculomotor (Third cranial nerve)

• The oculomotor nerve is entirely motor nerve.• Supplies Levator palpabrae superioris and all extrinsic

muscle of eye except lateral rectus and superior oblique.

• Also innervates sphincter pupillae and cilliary muscle.

Functional components :-1. Somatic efferent – concerned with

movements of eyeball.2. General visceral efferent – accomodation and

contraction of the pupil.3. General somatic afferent – proprioception.

Nucleus • Is a nuclear complex

made up of cell column and discrete nuclei.

• Lies ventral to the grey matter around the cerebral aqueduct, at the level of superior collicuius.

• Superiorly it approaches the floor of 3rd ventricle, inferiorly it is continous with the trochlear nerve nucleus.

• Consists of :• 1. Main oculomotor nucleus(large multipolar

cells) 2.Edinger – westphal or accessory oculomotor

nucleus(small multipolar cells)

Main motor nucleus:

1. One centrally placed caudal nucleus supplies to both LPS.

2. Four lateral paired subnuclei that innervate Superior rectus(paramedial), Inferior rectus(dorsolateral), Inferior oblique(intermedial). Medial rectus(ventromedial)

– Axons from one superior rectus (SR) subnucleus cross and pass through the opposite SR subnucleus , to innervate cotralateral sup. rectus thus, a lesion of one SR subnucleus results in bilateral superior rectus palsy.

– LPS has bilateral supply while All other EOM get ipsilateral supply

Course and relation • Efferent fibres from 3rd

nerve nucleus.• Pass through medial

longitudinal fasciculus, red nucleus, substantia nigra and medial aspect of cerebral peduncle.

• Emerges from ventral aspect of mid brain and pass into interpeduncular space.

• Nerve descends anteriorly in interpeduncular fossa between post. Cerebral and sup. Cerebellar arteries.

• Unaccompanied by any other cr. nerve (isolated 3rd nerve palsies are frequently basilar).

• passing forward it is superomedial to trochlear nerve and inferolateral and parallel to post. Communicating artery.

• It pierce the dura b/w free and attached margin of tentorium, to reach the cavernous sinus.

• It traverse the post. Part

of roof of the sinus to reach its lateral wall.

• In the wall trochlear nerve and 1st & 2nd divisions of trigeminal nerve are inferolateral to it.

• abducent nerve and internal carotid artery are Inferomedial.

• At the anterior part of sinus nerve divides into a small superior and larger inferior branch.

• These two divisions of nerve enter the orbit through middle part of sup. Orbital fissure(in annulus of zinn).

• Nerve is crossed by trochlear nerve which become superomedial to it. Abducent nerve lies first inferior then lateral to the divisions of nerve. Trochlear, frontal and lacrimal nerves traverse the fissure above the anulus of zinn.

two divisions:1. Superior division: diverges medially above

the optic nerve and behind the nasocilliary nerve.Supplys to sup. rectus and levator palpebrae superioris muscles.

2. Inferior division:• Divides immediately into branches to supply-

medial rectus, inferior rectus and inferior oblique muscle.

• Nerve to inf. Oblique enters the muscle as 2-3 branches, it also supplies a ramus to cilliary ganglion.

Cilliary ganglion

Roots of cilliary ganglon:1. Sensory root: comes from nasocilliary nerve2. Parasypathetic root: arise from nerve to inf. Oblique

muscle.3. Sympathetic root: is a branch from int. carotid plexus.

• Branches :• Gives 15-20 short cilliary nerve.• Contains fibres of all three roots of cilliary

ganglion.

Edinger-Westphal: • Parasympathetic nucleus.• interposed between two main

nuclei.• Composed of small multipolar

cells of preganglionic autonomic type.

• Preganglionic neuronal axons from this form the visceral component of oculomotor nerve.

• Earlier regarded as pupillomotor centre.

Location of Pupillomotor fibres

In the part of oculomotor nerve which lies between brainstem and cavernous sinus, the pupillomotor parasympathetic fibres are located superficially and superomedially

• Oculomotor nerve gets blood supply from various branches from basilar artery(in brain stem) and int.& ext carotid artery.

• Pupillomotor fibres derive their blood supply from the pial blood vessels, whereas the main trunk is supplied by vasa nervosum.

functions

• Elevation of lid (Levator palpabrae superioris)• All movements of eye, except lateral, down

and out movements.• Miosis,accomodation and light reflex

(Parasymp innervation)

Trochlear (4th cranial) nerve1. It is purely motor nerve, Supplys to sup.

Oblique muscle.2. The nerve is named for the trochlea, the

fibrous pulley through which the tendon of the superior oblique muscle passes.

3. It is crossed, most slender, smallest nerve and has longest intra cranial course(7.5cm) of all cranial nerves.

4. It is Only cranial nerve to emerge from dorsal aspect of brain.

FUNCTIONAL COMPONENETS :-

1. Somatic efferent – concerned with the movement of eyeball.

2. General somatic afferent – carries proprioceptive impulses from S.O. muscle to the mesencephalic nucleus of trigeminal nerve.

Nucleus • Trochlear nucleus

situated At the level of sup. border of inferior colliculus.

• It is In the dorsum of tegmentum of mid brain, ventrolateral to the cerebral aqueduct.

• Dorsal to the medial longitudinal fasciculus.

• continous with 3rd nerve nucleus superiorly.

Course and relation• From each nucleus nerve fibres first run laterally

to mesencephalic nucleus of 5th nerve, then somewhat downwards and parallel to aqueduct

• At lower border of inf. Colliculus they turn medially to decussate in superior medullary velum.

• Hence each sup. Oblique is supplied from contralateral trochlear nucleus.

• After crossing in sup. Medullary velum the Nerve emerge on dorsal aspect of sup. Cerebellar peduncle, then curves around the peduncle at upper border of pons.

•

•

• Passes b/w post. Cerebral & sup. Cerebellar arteries. While this course nerve is inferomedial to free margins of tentorium.

• Nerve enters in cavernous sinus on post. Part of its roof and goes to its lateral wall.

• where it is supero medial to1st & 2nd division of trigeminal nerve, abducent nerve& int. carotid artery.

• While passing through the sinus Oculomotor nerve first superomedial to trochlear nerve

• then trochlear nerve cross over and become itself medial to it at the entry in superior orbital fissure.

• Trochlear nerve run in upper region of fissure above the annular tendon where Frontal & lacrimal nerves are superolateral to it.

• The nerve enter in orbit and fans out into 3-4 branches to supply sup. Oblique muscle on its sup. Surface.

• Number of fibres in intraorbital part of trochlear nerve are greater than its intracranial part.

• These extra fibres carrying the proprioceptive impulses from sup. Oblique muscle, leave the trochlear nerve to join ophthalmic division of the 5th nerve, in the cavernous sinus.

• Ultimately these fibres relay in mesencephalic nucleus of 5th nerve.

Function

• Sup. Oblique muscle Primarily rotates the tip of the eye towards the nose (Intorsion)

• Secondarily moves the eye downwards (depression)

• Tertiary function is to moves the eye outwards ( abduction)

• Trochlear nerve typically allows a person to view the tip of his or her nose.

Abducent (sixth cranial) nerve• Entirely motor nerve, supplys to lateral rectus

muscle.• Most vulnerable cranial nerve, to damage in

traumas involving cranium.

FUNCTIONAL COMPONENT :

1.Somatic efferent – for lateral movement of eye.

2.General somatic afferent : for proprioceptive impulses which are carried to mesencephalic nucleus of 5th nerve.

Nucleus • Abducent nucleus is Small mass of large

multipolar cells, in floor of fourth ventricle, ventral to colliculus fascialis. where it is closely related to the horizontal gaze centre(PPRF).

• fasciculus of the 7th nerve curves around the abducent nucleus.

• Numerous small multipolar cells intermingled

with these large cells which form so called nucleus para-abducens.

• Fibres from these cells relay in the oculomotor nucleus via medial longitudinal fasciculus.

Course and relation• Efferent fibre starts from nucleus, traverse

through tegmentum, Parapontine raticular formation(pprf) and pyramidal tract .

• Then leave the brainstem at pontomedullary junction, just lateral to pyramidal prominance.

• Lateral to each abducent there is the emergence of facial nerve.

• B/w two Abducent nerves there is basilar

artery at its formation.• just after emergence, nerve enters in

prepontine basilar cistern. Then it passes upwards close to the base of skull and is crossed by ant. Inf. Cerebellar artery.

• It pierces the dura below the post. Clinoid and angles forwards over the tip of petrous temporal bone.

• Nerve passes around inf.Petrosal sinus in anterolateral direction,under the petroclinoid ligament(dorello canal), to enter in cavernous sinus.

• In sinus Nerve runs forwards almost horizontally, being inferolateral to int. carotid artery and its symp. Plexus.

• Abducent nerve is usually in the sinus.• Nerve runs out, at ant. end of sinus and enter in

sup. Orbital fissure.

• It traverse the fissure through its middle part within annulus of zinn.

• At first it is below the divisions of 3rd nerve then in b/w the two divisions.

• It is lateral to nasocilliary nerve.

In the orbit:

• Nerve divides into 3-4 filaments which enter the ocular surface of lateral rectus muscle behind its mid point.

• Function: • Lateral movement of

eye.

variations in 6th nerve:• nerve may arise by 2 roots, which pass

separately to the sup. Orbital fissure.• It may give rise to a branch to cilliary ganglion.• The nasocilliary nerve may be a branch of it.• Abducent nerve may be absent, being

replaced by oculomotor nerve.

References

• Wolfs anatomy of eye and orbit; 8th edition.• Kanski bowlings clinical ophthalmology; 7th

edition.• Adler’s physiology of eye, 6th edition.• Gray’s gross anatomy, 27th edition.• Anatomy and physiology of eye, ak khurana;

2nd edition.

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