Cranial Nerve III: Oculomotor Nerve Anatomy

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Cranial Nerve III: Oculomotor Nerve

The oculomotor nerve provides motor innervation to some extraocular muscles and the eye itself, but no sensory information. It allows for movement of the eye via the superior rectus, inferior rectus, medial rectus, and inferior oblique. The oculomotor nerve also innervates the sphincter pupillae for pupil constriction (such as when facing direct light or reading a book), the ciliary muscle for lens accommodation, and the levator palpebrae for opening the eyelid.

The two pairs of nuclei of the oculomotor nerve, oculomotor nuclei and Edinger-Westphal nuclei, are located in the midbrain :

The oculomotor nucleus is responsible for movement by the levator palpebrae, superior rectus, medial rectus, inferior rectus, and inferior oblique.
The Edinger-Westphal nucleus carries parasympathetic information to the ciliary ganglion, which innervates the ciliary and pupillary sphincter muscles to allow accommodation and pupil constriction.

The oculomotor nerve leaves the nuclei and passes ventrally through the red nucleus and crus cerebri. It exits the brainstem in the interpeduncular fossa. The nerve enters the subarachnoid space, passes into the lateral wall of the cavernous sinus, and enters the orbit via the superior orbital fissure, where it splits into a superior and an inferior segment:

The superior division innervates the levator palpebrae and superior rectus.
The inferior segment innervates the medial rectus, inferior rectus, inferior oblique, pupillary sphincter, and ciliary muscle.


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