The pupil constricts in response to light due to which cranial nerve?

The pupil constricts in response to light due to which cranial nerve?

• A. Oculomotor
• B. Optic
• C. Trochlear
• D. Abducens

Answer: (A)

Pupillary constriction in response to light is driven by the parasympathetic output of the oculomotor nerve. Light is detected by the retina and carried via the optic nerve to brainstem circuits, which send the efferent signal back along the oculomotor nerve to the sphincter pupillae muscle of the iris (via the ciliary ganglion). When this parasympathetic pathway is activated, the pupil constricts. The other nerves don’t control this reflex: the optic nerve is the afferent limb that senses light, while the trochlear and abducens nerves mainly govern eye movements.

Pupillary constriction in response to light is driven by the parasympathetic output of the oculomotor nerve. Light is detected by the retina and carried via the optic nerve to brainstem circuits, which send the efferent signal back along the oculomotor nerve to the sphincter pupillae muscle of the iris (via the ciliary ganglion). When this parasympathetic pathway is activated, the pupil constricts. The other nerves don’t control this reflex: the optic nerve is the afferent limb that senses light, while the trochlear and abducens nerves mainly govern eye movements.