The trochlear nerve is the 4th cranial nerve. It is the smallest cranial nerve and, has the longest pathway. It has a purely somatic motor function. The trochlear nerve emerges from the trochlear nucleus (is located in the midbrain, at the level of the inferior colliculus ) or from the dorsal (near the back) side of the midbrain (uniquely), just below inferior colliculus. It runs anteriorly and inferiorly within the subarachnoid space before penetrating the dura mater adjacent to the posterior clinoid process of the sphenoid bone. The nerve then progresses to the lateral wall of the cavernous sinus before reaching the orbit of the eye via the superior orbital fissure. The trochlear nerve supplies a single muscle – superior oblique that muscle
