Which statement about the Trochlear nerve (CN IV) is NOT true?

Which statement about the Trochlear nerve (CN IV) is NOT true?

• A. It has the longest course of the cranial nerves
• B. It is located in the midbrain at the level of the superior colliculus
• C. It is the skinniest cranial nerve
• D. It exits the brainstem dorsally

Answer: (B)

Trochlear nerve fibers originate in the dorsal midbrain, with its nucleus tucked near the inferior colliculus. The fibers then decussate and exit the brainstem from the dorsal surface, wrapping around the brainstem before continuing to the orbit. That dorsal exit is a defining feature and explains why this nerve has the longest intracranial course. The level of the midbrain where the nucleus sits is around the inferior, not the superior, colliculus, so saying it lies at the level of the superior colliculus is not true. The other statements are correct: it is the skinniest cranial nerve, and it indeed has the longest course within the cranial nerves.

Trochlear nerve fibers originate in the dorsal midbrain, with its nucleus tucked near the inferior colliculus. The fibers then decussate and exit the brainstem from the dorsal surface, wrapping around the brainstem before continuing to the orbit. That dorsal exit is a defining feature and explains why this nerve has the longest intracranial course. The level of the midbrain where the nucleus sits is around the inferior, not the superior, colliculus, so saying it lies at the level of the superior colliculus is not true. The other statements are correct: it is the skinniest cranial nerve, and it indeed has the longest course within the cranial nerves.