Site of postganglionic nerve cells that elicit dilation of pupil?

• A. Superior cervical ganglion
• B. Ciliary ganglion
• C. Otic ganglion
• D. Pterygopalatine ganglion

Answer: (A)

Dilation of the pupil is controlled by sympathetic input to the dilator pupillae muscle, and the cell bodies for that postganglionic supply reside in the superior cervical ganglion. Preganglionic fibers from T1–T2 ascend in the sympathetic chain to this ganglion, synapse there, and the postganglionic fibers hitch a ride with the internal carotid artery plexus, reaching the eye via the long ciliary nerves to stimulate the dilator pupillae and cause mydriasis. The ciliary ganglion houses parasympathetic postganglionic neurons that innervate the sphincter pupillae (pupil constriction), not the dilator. The otic and pterygopalatine ganglia are parasympathetic relays for other targets (like salivary and lacrimal/nasal glands) and do not mediate pupil dilation.