Which cranial nerve has the longest course and is considered the skinniest cranial nerve?

• A. CN II
• B. CN III
• C. CN IV
• D. CN V

Answer: (C)

The trochlear nerve is the one that travels the farthest inside the skull while remaining extremely slender. It starts from the trochlear nucleus in the dorsal midbrain, exits the brainstem on its dorsal surface, then wraps around the cerebral peduncle and courses in the subarachnoid space to reach the cavernous sinus and finally passes through the superior orbital fissure to innervate the superior oblique muscle. That long intracranial path combined with a very small diameter makes it the longest “line” inside the skull and the skinniest cranial nerve. Other nerves may have long routes or large diameters, but none pair both features as this one does.