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The third cranial nerve.
The oculomotor nerve is the third cranial nerve (CN III).
The oculomotor nerve (CN III) arises from the anterior aspect of mesencephalon (midbrain).
It originates from the third nerve nucleus at the level of the superior colliculus in the midbrain.
There are two nuclei for the oculomotor nerve.
The third nerve nucleus is located ventral to the cerebral aqueduct, on the pre-aqueductal grey matter.
The fibers from the two third nerve nuclei located laterally on either side of the cerebral aqueduct then pass through the red nucleus.
From the red nucleus fibers then pass via the substantia nigra exiting through the interpeduncular fossa.
On emerging from the brainstem, It passes between the superior cerebellar and posterior cerebral arteries 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.
The oculomotor nerve 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.
As the oculomotor nerve enters the orbit it divides into a superior and an inferior branch.
From its origin in the oculomotor nucleus, Edinger-Westphal nucleus
to its superior and inferior branch, it innervates the superior rectus, inferior rectus, medial rectus, inferior oblique, levator palpebrae superioris, sphincter pupillae (parasympathetics), ciliaris muscle (parasympathetics).
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.
The nerve, in addition, contains fibers that innervate the intrinsic eye muscles that enable pupillary constriction and accommodation.
The Edinger-Westphal nucleus supplies parasympathetic fibers to the eye via the ciliary ganglion, and thus controls the sphincter pupillae muscle that affects pupil constriction and the ciliary muscle, affecting accommodation.
The oculomotor nerve controls the constriction of the pupils and thickening of the lens of the eye, and can be tested moving a finger toward a person’s face to induce accommodation, their pupils should constrict.
Shining a light into one eye should result in equal constriction of the other eye.
Loss of accommodation and continued pupillary dilation can indicate the presence of a lesion on the oculomotor nerve.
It enters the orbit via the superior orbital fissure and innervates muscles that enable most movements of the eye and that raise the eyelid.
The superior branch of the oculomotor nerve or the superior division, supplies the superior rectus and levator palpebrae superioris.
These branches enter the muscles on their ocular surfaces, with the exception of the nerve to the inferior oblique, which enters the muscle at its posterior border.
Sympathetic postganglionic fibers join the nerve from the plexus on the internal carotid artery in the wall of the cavernous sinus and are distributed to the smooth muscle of superior tarsal muscle.
The inferior branch of the oculomotor nerve or the inferior division, divides into three branches.
One passes beneath the optic nerve to the medial rectus, and another, to the inferior rectus.
The third and longest runs forward between the inferior recti and lateralis to the inferior oblique.
From the third one, a short branch is given off to the lower part of the ciliary ganglion.
The nerve also contains fibers that innervate the muscles that enable pupillary constriction and accommodation.
It is derived from the embryonic midbrain.
Cranial nerves IV and VI also participate in control of eye movements.
Innervates Superior rectus, Inferior rectus, Medial rectus, Inferior oblique, Levator palpebrae, sphincter pupillae (parasympathetics), ciliaris muscle (parasympathetics).
The oculomotor nerve include axons which innervate skeletal muscle of the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles.
It innervates all the extrinsic muscles except superior oblique and lateral rectus.
The nerve also includes axons which provide preganglionic parasympathetics to the ciliary ganglion.
From the ciliary ganglion post ganglionic fibers pass through the short ciliary nerve to the constrictor pupillae of the iris and the cilliary muscles.
Damage to this nerve, termed oculomotor nerve palsy, is known by its down and out symptoms, because of the position of the affected eye-lateral, downward deviation of gaze.
direct trauma,
demyelinating diseases
increased intracranial pressure.
due to a space-occupying lesion.
spontaneous subarachnoid hemorrhage
microvascular disease.
In diabetes patients older than 50 years of age, an oculomotor nerve palsy, occurs with preservation of the pupillary reflex.
In the oculomotor nerve fibers controlling the pupillary function are superficial and spared from ischemic injuries typical of diabetes.
Aneurysms which lead to compression of the oculomotor nerve affects the superficial fibers and manifests as a third nerve palsy with loss of the pupillary reflex
Third nerve palsy with loss of pupillary reflex is considered to represent an aneurysm.
Cranial nerves III, IV, and VI are tested together as part of the cranial nerve examination.
By observing the eye movement and eyelids information is obtained about the extraocular muscles, the levator palpebrae superioris muscle, and cranial nerves III, IV, and VI.
Loss of function of any of the eye muscles results in ophthalmoparesis.
The oculomotor nerve controls most of the eye muscles.
Oculomotor nerve palsy is also known by the down ‘n out symptoms, because of the position of the affected eye is lateral, and a downward deviation of gaze.
The oculomotor nerve also controls the constriction of the pupils and thickening of the lens of the eye.
Shining a light into one eye should result in equal constriction of the other eye.
The neurons in the optic nerve decussate in the optic chiasm with some crossing to the contralateral optic nerve tract.”.
Loss of accommodation and continued pupillary dilation can indicate the presence of a lesion on the oculumotor nerve.