Oculomotor nerve

The oculomotor nerve (III) is a predominantly motor cranial nerve that supplies several extraocular muscles and also carries parasympathetic fibers involved in pupillary constriction and accommodation.

Number : III

Sensory, motor, or both : motor, with parasympathetic fibers

Origin : oculomotor nuclei in the rostral mesencephalon, adjacent to the midline and ventral to the mesencephalic aqueduct; parasympathetic fibers arise from the parasympathetic nucleus of the oculomotor nerve.

Route / Reports : the fibers pass ventrally through the tegmentum and emerge from the mesencephalon in the interpeduncular fossa, medial to the crus cerebri. The nerve then courses rostrally through the middle cranial fossa, lateral to the hypophysis and dorsal to the cavernous sinus, and leaves the cranial cavity through the orbital fissure.

Distribution : in the orbit, it divides into a dorsal branch supplying the dorsal rectus and levator palpebrae superioris muscles, and a ventral branch supplying the medial rectus, ventral rectus, and ventral oblique muscles. Its parasympathetic fibers synapse in the ciliary ganglion and continue through the short ciliary nerves to the ciliary muscle and sphincter of the iris.

Description : The oculomotor nerve originates in the rostral mesencephalon, emerges ventrally in the interpeduncular fossa, passes through the middle cranial fossa, and enters the orbit through the orbital fissure. It then divides into dorsal and ventral branches that innervate most of the extraocular muscles, while its parasympathetic component reaches the ciliary ganglion and controls the ciliary muscle and pupillary sphincter.