Oculomotor Nerve

Description

Emerging from the ventral midbrain, the oculomotor nerve (cranial nerve III) courses anteriorly through the interpeduncular cistern, running between the posterior cerebral and superior cerebellar arteries and lying lateral to the posterior communicating artery as it approaches the cavernous sinus. Its parasympathetic component from the Edinger Westphal nucleus travels with the main trunk toward the orbit, where it will synapse in the ciliary ganglion. Within the orbit, the nerve divides into superior and inferior divisions that distribute motor axons to the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique, with short ciliary nerves carrying postganglionic fibers to the sphincter pupillae and ciliary muscle. A large caliber nerve. Fascicles and axons can be appreciated. That proximal segment is the one clinicians think about when a patient presents with a painful third nerve palsy and a dilated pupil, because a posterior communicating artery aneurysm can compress the superficially located parasympathetic fibers before frank ophthalmoplegia develops. By contrast, ischemic microvascular palsy in diabetes often spares the pupil because the vasa nervorum supply the core of the nerve more than the peripheral pupillomotor fibers. The arterial relationships along the cisternal course also explain why subarachnoid hemorrhage and basilar apex pathology can produce combined ocular motility deficits. Use this artwork in neuroanatomy and head and neck teaching modules to anchor the midbrain to orbital muscle map, or in neurology and neurosurgery texts when discussing aneurysm localization, cavernous sinus syndromes, and pupillary findings. It also fits well in ophthalmology materials covering extraocular muscle innervation and the neuroanatomy behind diplopia workups. Anatomical accuracy verified by SciePro's Medical Advisory Board.