Pupillary light reflex involves which cranial nerves?

Pupillary light reflex involves which cranial nerves?

• A. II and III
• B. II only
• C. III only
• D. II, III, V

Answer: (A)

The pupillary light reflex uses both the optic nerve as the sensory (afferent) limb and the oculomotor nerve as the motor (efferent) limb. Light hits the retina and signals travel via CN II to the brain, then CN III carries the parasympathetic output to the iris sphincter to cause pupil constriction. The trigeminal nerve isn’t part of this reflex arc, so it doesn’t contribute to constriction. Therefore, the necessary nerves are the optic and the oculomotor nerves.

The pupillary light reflex uses both the optic nerve as the sensory (afferent) limb and the oculomotor nerve as the motor (efferent) limb. Light hits the retina and signals travel via CN II to the brain, then CN III carries the parasympathetic output to the iris sphincter to cause pupil constriction. The trigeminal nerve isn’t part of this reflex arc, so it doesn’t contribute to constriction. Therefore, the necessary nerves are the optic and the oculomotor nerves.