Question

which cranial nerve mediates the efferent limb of the pupillary light reflex?
oculomotor (cn 3)
optic (cn 2)
trochlear (cn 4)
facial (cn 7)

Explanation:

The pupillary light reflex involves an afferent (sensory) limb and an efferent (motor) limb. The optic nerve (CN 2) is the afferent limb, transmitting visual information (light stimulus) to the brain. The oculomotor nerve (CN 3) is the efferent limb. It carries the motor signal from the brain to the pupillary sphincter muscle, causing the pupil to constrict. The trochlear nerve (CN 4) controls one of the extra - ocular muscles (superior oblique), and the facial nerve (CN 7) is mainly involved in facial expression, taste (anterior 2/3 of the tongue), and salivary gland function, not the pupillary light reflex efferent limb.

Answer:

Oculomotor (CN 3)