Which cranial nerve is primarily responsible for eye movements and pupil constriction?

• A. Trigeminal nerve — facial sensation
• B. Oculomotor nerve — eye movements and pupil constriction
• C. Vestibulocochlear nerve — hearing and balance
• D. Hypoglossal nerve — tongue movement

Answer: (B)

The oculomotor nerve is responsible for both eye movements and pupil constriction. It innervates most of the extraocular muscles that move the eye and also the levator palpebrae to raise the eyelid. In addition, it carries parasympathetic fibers that travel to the ciliary ganglion and then to the sphincter pupillae, causing the pupil to constrict and the lens to adjust for near vision. Clinically, this nerve handles the efferent limb of the pupillary light reflex, linking the retina’s detection of light to constriction of the pupil. The other nerves listed control different functions—facial sensation and chewing (trigeminal), hearing and balance (vestibulocochlear), and tongue movement (hypoglossal)—and do not primarily govern eye movements and pupil size.