Question

Human Physiology

Which of these is a cranial nerve that produce the pupillary reflex responde?

a)vagus nerve

b)phrenic nerve

c)optic nerve

d)vestibulochochleear nerve

e) occulomoter nerve

Answer 1

Option E-Occulomotor Nerve.

The pupillary light reflex or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity of light that falls on the retinal ganglion cells of the retina in the back of the eye.

Pupillary Reflex Pathway- The pupillary light reflex requires CN II, CN III, and central brain stem connections. Light shined in one eye stimulates retinal photoreceptors, and subsequently retinal ganglion cells, whose axons travel through the optic nerve.The afferents are optic nerve fibres which pass to both pretectal nuclei, crossing in the posterior commissure. Pretectal nuclei project to the Edinger-Westphal nucleus, from which parasympathetic efferents traverse the oculomotor nerves to ciliary ganglia, whence postganglionic fibres in short ciliary nerves innervate the sphincter pupillae muscles.

Role of Optic Nerve-

The optic nerve, or more precisely, the photosensitive ganglion cells through the retinohypothalamic tract, is responsible for the afferent limb of the pupillary reflex; it senses the incoming light.

Role of Occulomotor Nerve

The oculomotor nerve is responsible for the efferent limb of the pupillary reflex; it drives the iris muscles that constrict the pupil.

Both Optic nerve and occuolomotor nerves are involved in pupillary reflex.But,The nerve that produce the reponse(Contraction of pupil by contraction of sphincter pupillae)is Occulomotor nerve which supplies Sphincter pupillae muscle