Oculomotor Nerves

the third pair of cranial nerves. The fibers that constitute the nerve are processes of cells lying in the nuclei of the midbrain. The motor nucleus is located at the level of the superior colliculus in brain tissue, and the autonomic nucleus is located near it.

Nerve fibers emerge from the brain stem onto the inner surface of the cerebral peduncles, forming a comparatively large nerve that advances in the external wall of the cavernous sinus. On the way to the cavernous sinus this nerve is joined by nerve fibers of the sympathetic plexus of the internal carotid artery. The oculomotor nerve passes through the superior orbital fissure to the orbital cavity, where it divides into a smaller upper branch, which innervates the rectus superior oculi and the muscle that raises the upper eyelid, and a lower branch that contains motor fibers for the rectus medialis bulbi, rectus inferior bulbi, and obliquus inferior bulbi. A nerve tract containing autonomic parasympathetic fibers separates from the lower branch and continues to the ciliary ganglion situated between the optic nerve and the rectus lateralis bulbi. The parasympathetic fibers that innervate the smooth muscles of the ciliary body (for accommodation) and the iris (a muscle that causes the pupil to contract) originate in the cells of the ciliary ganglion.