The Trochlear Nerve (Cranial Nerve IV)

The trochlear nerve, also called the fourth cranial nerve or CN IV, is a motor nerve Opens in new window (a somatic Opens in new window efferent nerve) that innervates only a single muscle: the superior oblique muscle Opens in new window of the eye, which operates through the pulley Opens in new window-like trochlea[1] Opens in new window.
Homologous Opens in new window trochlear nerves are found in all jawed vertebrates Opens in new window. The unique features of the trochlear nerve, including its dorsal exit from the brainstem and its contralateral innervation, are seen in the primitive brains of sharks[2 Opens in new window].


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  2. Bisaria KK. Cavernous portion of the trochlear nerve with special reference to its site of entrance. J. Anat. 159:29-35, 1988