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Oculomotor Nerve
Nervous System

Oculomotor Nerve

Nervus oculomotorius

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Quick Facts

Origin: Midbrain.

Course: Runs ventrally from the midbrain into the cavernous sinus, passes through the superior orbital fissure to enter the orbit.

Branches: Superior and inferior branches, branch to ciliary ganglion.

Supply: Extraocular muscles, sphincter pupillae muscle, and ciliary muscle.

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Origin

The oculomotor nerve originates primarily in the oculomotor nucleus of the midbrain (mesencephalon). Parasympathetic fibers that travel with the oculomotor nucleus originate in the Edinger-Westphal nucleus.

The oculomotor nerve emerges from the brain on the ventral surface of the brainstem, at the junction of the midbrain and pons, just medial to the cerebral peduncle.

Course

From its origin at the ventral surface of the midbrain, the oculomotor nerve runs anteriorly. It is typically found between the posterior cerebral artery and the superior cerebellar artery. Shortly thereafter, the nerve pierces the dura and passes through the cavernous sinus on its way through the superior orbital fissure and on into the orbit.

Branches

The oculomotor nerve splits into two branches, the superior and inferior branches of the oculomotor nerve, as it passes through the common tendinous ring of the extraocular muscles.

The superior branch of the oculomotor nerve conveys somatic efferent fibers to the superior rectus and levator palpebrae superioris muscles.

The inferior branch of the oculomotor nerve conveys somatic efferent fibers to the inferior rectus, inferior oblique, and medial rectus muscles. It also conveys parasympathetic fibers to the ciliary ganglion.

Supplied Structures

The oculomotor nerve is a motor nerve carrying efferent fibers that are either somatic or autonomic in nature.

The somatic fibers innervate the levator palpebrae superioris muscle and most of the extraocular muscles of the eye, including the medial rectus, superior rectus, inferior rectus, and inferior oblique muscles.

Parasympathetic fibers originating in the Edinger-Westphal nucleus synapse on the ciliary ganglion. The ultimate targets are the sphincter pupillae muscle and the ciliary muscles of the eye. These constrict the pupil and increase the curvature of the lens, respectively.

Sympathetic fibers from the carotid plexus join the oculomotor nerve as it passes through the cavernous sinus. These run to the orbit via the inferior branch of the oculomotor nucleus and the ciliary ganglion.

List of Clinical Correlates

—Pupillary light reflex

—Accommodation reflex

—Strabismus

—Ptosis

—Diplopia

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