Which nerve provides the parasympathetic innervation to constrict the pupil during the pupillary light reflex?

Which nerve provides the parasympathetic innervation to constrict the pupil during the pupillary light reflex?

• A. CN III (oculomotor) provides the parasympathetic innervation to constrict the pupil.
• B. CN II is the parasympathetic to constrict the pupil.
• C. CN IV is responsible for constriction.
• D. CN VI constricts the pupil.

Answer: (A)

Parasympathetic control of pupil constriction during the pupillary light reflex 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 reach the iris sphincter muscle via the short ciliary nerves to cause constriction. The optic nerve (CN II) provides the sensory input for the reflex but does not mediate constriction. The trochlear (CN IV) and abducens (CN VI) nerves control eye movements and do not carry the parasympathetic fibers to the pupil.

Parasympathetic control of pupil constriction during the pupillary light reflex 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 reach the iris sphincter muscle via the short ciliary nerves to cause constriction. The optic nerve (CN II) provides the sensory input for the reflex but does not mediate constriction. The trochlear (CN IV) and abducens (CN VI) nerves control eye movements and do not carry the parasympathetic fibers to the pupil.