Trochlear Nerve - Peripheral Anatomy

Peripheral Anatomy

The trochlear nerve emerges from the dorsal aspect of the brainstem at the level of the caudal mesencephalon, just below the inferior colliculus. It circles anteriorly around the brainstem and runs forward toward the eye in the subarachnoid space. It passes between the posterior cerebral artery and the superior cerebellar artery, and then pierces the dura just under free margin of the tentorium cerebelli, close to the crossing of the attached margin of the tentorium and within millimeters of the posterior clinoid process. It runs on the lateral wall of the cavernous sinus, where it is joined by the other two extraocular nerves (III) and the first two branches of the trigeminal nerve (V), Ophthalmic V1 and Maxillary V2. The internal carotid artery and Abducens nerve (VI) run within the cavernous sinus. Finally, it enters the orbit through the superior orbital fissure and innervates the superior oblique muscle.

The superior oblique muscle ends in a tendon that passes through a fibrous loop, the trochlea, located anteriorly on the medial aspect of the orbit. Trochlea means “pulley” in Latin; the fourth nerve is named after this structure.