Which nerve provides parasympathetic innervation to the pupil?

• A. Optic nerve (CN II)
• B. Trigeminal nerve (CN V)
• C. Oculomotor nerve (CN III)
• D. Abducens nerve (CN VI)

Answer: (C)

Parasympathetic control of the pupil is carried by the oculomotor nerve. The parasympathetic fibers originate in the Edinger-Westphal nucleus, travel with the oculomotor nerve to the ciliary ganglion, and then postganglionic fibers in the short ciliary nerves innervate the sphincter pupillae. When stimulated, the sphincter pupillae constricts the pupil, narrowing the aperture in bright light or during accommodation. The optic nerve is purely sensory, the trigeminal nerve handles sensory and some motor functions in the face but not parasympathetic innervation to the pupil, and the abducens nerve controls the lateral rectus muscle without parasympathetic involvement to the pupil.