Which cranial nerve provides parasympathetic fibers that control pupil constriction?

Which cranial nerve provides parasympathetic fibers that control pupil constriction?

• A. CN II
• B. CN III
• C. CN VII
• D. CN X

Answer: (B)

Parasympathetic control of pupil constriction travels with the oculomotor nerve. The preganglionic parasympathetic fibers originate in the Edinger-Westphal nucleus, travel with CN III, synapse in the ciliary ganglion, and then the postganglionic fibers reach the sphincter pupillae via the short ciliary nerves to constrict the pupil in response to light or accommodation. The optic nerve is involved in vision but carries no parasympathetic fibers; the facial nerve mainly supplies lacrimal and some salivary glands; the vagus nerve runs parasympathetic fibers to thoracic and abdominal organs.

Parasympathetic control of pupil constriction travels with the oculomotor nerve. The preganglionic parasympathetic fibers originate in the Edinger-Westphal nucleus, travel with CN III, synapse in the ciliary ganglion, and then the postganglionic fibers reach the sphincter pupillae via the short ciliary nerves to constrict the pupil in response to light or accommodation. The optic nerve is involved in vision but carries no parasympathetic fibers; the facial nerve mainly supplies lacrimal and some salivary glands; the vagus nerve runs parasympathetic fibers to thoracic and abdominal organs.