The trochlear nucleus corresponds to which cranial nerve?

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

Answer: (C)

The main concept here is that the trochlear nucleus is the motor nucleus for the fourth cranial nerve. It sits in the midbrain and gives rise to the trochlear nerve, which fibers cross and exit dorsally to innervate the superior oblique muscle. This muscle helps depress and intort the eye, especially when it’s adducted, so the nerve controls downward and outward gaze.

That’s why the correct pairing is the trochlear nerve (cranial nerve IV). The other options refer to different nerves or modalities: the optic nerve is purely sensory (no motor nucleus), the oculomotor nerve has its own motor nucleus in the midbrain but is not the trochlear nucleus, and the abducens nerve (cranial nerve VI) supplies the lateral rectus with its own nucleus in the pons.