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Cranial nerves

cranial nervecranialCN
The oculomotor nerve is the third cranial nerve (CN III).
Most typically, humans are considered to have twelve pairs of cranial nerves (I–XII), with the terminal nerve (0) more recently canonized . They are: the olfactory nerve (I), the optic nerve (II), oculomotor nerve (III), trochlear nerve (IV), trigeminal nerve (V), abducens nerve (VI), facial nerve (VII), vestibulocochlear nerve (VIII), glossopharyngeal nerve (IX), vagus nerve (X), accessory nerve (XI), and hypoglossal nerve (XII).

Orbit (anatomy)

orbitorbitseye socket
It enters the orbit via the superior orbital fissure and innervates extrinsic eye muscles that enable most movements of the eye and that raise the eyelid.
In the adult human, the volume of the orbit is 30 ml, of which the eye occupies 6.5 ml. The orbital contents comprise the eye, the orbital and retrobulbar fascia, extraocular muscles, cranial nerves II, III, IV, V, and VI, blood vessels, fat, the lacrimal gland with its sac and nasolacrimal duct, the eyelids, medial and lateral palpebral ligaments, check ligaments, the suspensory ligament, septum, ciliary ganglion and short ciliary nerves.

Superior orbital fissure

sphenoidal fissure
It enters the orbit via the superior orbital fissure and innervates extrinsic eye muscles that enable most movements of the eye and that raise the eyelid.
superior and inferior divisions of oculomotor nerve (III)

Eye movement

eye movementsversionmovements of the eye
It enters the orbit via the superior orbital fissure and innervates extrinsic eye muscles that enable most movements of the eye and that raise the eyelid. Cranial nerves IV and VI also participate in control of eye movement.
The muscles are supplied by the oculomotor nerve, with the exception of the superior oblique, which is supplied by the trochlear nerve, and the lateral rectus, supplied by the abducens nerve.

Superior cerebellar artery

superior cerebellarSCAsuperior cerebellar branches
It passes between the superior cerebellar (below) and posterior cerebral arteries (above), and then pierces the dura mater anterior and lateral to the posterior clinoid process, passing between the free and attached borders of the tentorium cerebelli.
It passes lateralward, immediately below the oculomotor nerve, which separates it from the posterior cerebral artery, winds around the cerebral peduncle, close to the trochlear nerve, and, arriving at the upper surface of the cerebellum, divides into branches which ramify in the pia mater and anastomose with those of the anterior and posterior inferior cerebellar arteries.

Trochlear nerve

trochlearIVfourth
Cranial nerves IV and VI also participate in control of eye movement.
It is immediately below the nucleus of the oculomotor nerve (III) in the rostral mesencephalon.

Brainstem

brain stembrain-stemback of the skull
On emerging from the brainstem, the nerve is invested with a sheath of pia mater, and enclosed in a prolongation from the arachnoid.
Oculomotor nerve nucleus: This is the third cranial nerve nucleus.

Ophthalmic nerve

ophthalmicophthalmic divisionophthalmic branch
It traverses the cavernous sinus, above the other orbital nerves receiving in its course one or two filaments from the cavernous plexus of the sympathetic nervous system, and a communicating branch from the ophthalmic division of the trigeminal nerve.
The ophthalmic nerve is joined by filaments from the cavernous plexus of the sympathetic, and communicates with the oculomotor, trochlear, and abducent nerves; it gives off a recurrent (meningeal) filament which passes between the layers of the tentorium.

Cavernous sinus

cavernouscavernous sinusescavernous sinus syndrome
It traverses the cavernous sinus, above the other orbital nerves receiving in its course one or two filaments from the cavernous plexus of the sympathetic nervous system, and a communicating branch from the ophthalmic division of the trigeminal nerve.
Oculomotor nerve

Oculomotor nucleus

oculomotor nucleiocular movement nucleusoculomotor
The oculomotor nucleus originates at the level of the superior colliculus. The muscles it controls are the striated muscle in levator palpebrae superioris and all extraocular muscles except for the superior oblique muscle and the lateral rectus muscle.
The fibers of the oculomotor nerve arise from a nucleus in the midbrain, which lies in the gray substance of the floor of the cerebral aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle.

Medial rectus muscle

medial rectusmedialmedial recti
One passes beneath the optic nerve to the medial rectus.
As with most of the muscles of the orbit, it is innervated by the inferior division of the oculomotor nerve (Cranial Nerve III).

Ciliary ganglion

ciliarylight-near dissociation
The third and longest runs forward between the inferior recti and lateralis to the inferior oblique. From the last a short thick branch is given off to the lower part of the ciliary ganglion, and forms its short root. The Edinger-Westphal nucleus supplies parasympathetic fibers to the eye via the ciliary ganglion, and thus controls the sphincter pupillae muscle (affecting pupil constriction) and the ciliary muscle (affecting accommodation).
The oculomotor nerve coming into the ganglion contains preganglionic axons from the Edinger-Westphal nucleus (a part of the brainstem) which form synapses with the ciliary neurons.

Inferior oblique muscle

inferior obliqueinferioroblique
The third and longest runs forward between the inferior recti and lateralis to the inferior oblique. From the last a short thick branch is given off to the lower part of the ciliary ganglion, and forms its short root.
The inferior oblique is innervated by the inferior branch of the oculomotor nerve.

Parasympathetic nervous system

parasympatheticparasympathetic nerveparasympathetic nerves
The Edinger-Westphal nucleus supplies parasympathetic fibers to the eye via the ciliary ganglion, and thus controls the sphincter pupillae muscle (affecting pupil constriction) and the ciliary muscle (affecting accommodation).
Specific nerves include several cranial nerves, specifically the oculomotor nerve, facial nerve, glossopharyngeal nerve, and vagus nerve.

Interpeduncular fossa

interpeduncular nucleus
From the red nucleus fibers then pass via the substantia nigra exiting through the interpeduncular fossa.
Contents of interpeduncular fossa include oculomotor nerve, and circle of willis.

Oculomotor nerve palsy

oculomotor palsyimpairment of cranial nerve IIIocculomotor nerve palsy
Paralysis of the oculomotor nerve, i.e., oculomotor nerve palsy, can arise due to:
As the name suggests, the oculomotor nerve supplies the majority of the muscles controlling eye movements.

Superior rectus muscle

superior rectussuperiorsuperior recti
It supplies the superior rectus and levator palpebrae superioris.
It is innervated by the superior division of the oculomotor nerve (Cranial Nerve III).

Inferior rectus muscle

inferior rectusinferiorinferior recti
Another, to the inferior rectus.
As with most of the muscles of the orbit, it is innervated by the inferior division of oculomotor nerve (Cranial Nerve III).

Cavernous nerve plexus

cavernous plexus
It traverses the cavernous sinus, above the other orbital nerves receiving in its course one or two filaments from the cavernous plexus of the sympathetic nervous system, and a communicating branch from the ophthalmic division of the trigeminal nerve.
It communicates with the oculomotor, the trochlear, the ophthalmic and the abducent nerves, and with the ciliary ganglion, and distributes filaments to the wall of the internal carotid artery.

Posterior cerebral artery

Posterior cerebralposterior cerebral arteriesinfarction, posterior cerebral artery
It passes between the superior cerebellar (below) and posterior cerebral arteries (above), and then pierces the dura mater anterior and lateral to the posterior clinoid process, passing between the free and attached borders of the tentorium cerebelli.
Ipsilateral deficits of oculomotor nerve,

Cerebral aqueduct

aqueduct of Sylviusaqueductalmesencephalic duct
The third nerve nucleus is located ventral to the cerebral aqueduct, on the pre-aqueductal grey matter.

Accommodation reflex

accommodationaccommodatingaccommodative
The Edinger-Westphal nucleus supplies parasympathetic fibers to the eye via the ciliary ganglion, and thus controls the sphincter pupillae muscle (affecting pupil constriction) and the ciliary muscle (affecting accommodation).
It is dependent on cranial nerve II (afferent limb of reflex), superior centers (interneuron) and cranial nerve III (efferent limb of reflex).

Cerebellar tentorium

tentorium cerebellitentoriuminfratentorial neoplasms
It passes between the superior cerebellar (below) and posterior cerebral arteries (above), and then pierces the dura mater anterior and lateral to the posterior clinoid process, passing between the free and attached borders of the tentorium cerebelli.
This is called herniation and will often cause an enlarged pupil on the affected side, due to pressure on the oculomotor nerve.

Extraocular muscles

extraocular muscleeye muscleseye muscle
The oculomotor nucleus originates at the level of the superior colliculus. The muscles it controls are the striated muscle in levator palpebrae superioris and all extraocular muscles except for the superior oblique muscle and the lateral rectus muscle.

Subarachnoid hemorrhage

subarachnoid haemorrhagesubarachnoidsubarachnoid hemorrhage, traumatic
spontaneous subarachnoid haemorrhage (e.g., berry aneurysm), and
Oculomotor nerve abnormalities (affected eye looking downward and outward and inability to lift the eyelid on the same side) or palsy (loss of movement) may indicate bleeding from the posterior communicating artery.