Sympathetic fibers that innervate Muller's muscle hitch a ride with which division of the oculomotor nerve?

• A. Superior division of CN III
• B. Inferior division of CN III
• C. CN II
• D. CN IV

Answer: (A)

The eyelid’s elevation relies on two muscles: the levator palpebrae superioris (somatic motor) and Muller's muscle (superior tarsal, smooth muscle) which is controlled by the sympathetic system. Postganglionic sympathetic fibers originate in the superior cervical ganglion and travel with the internal carotid plexus into the orbit. To reach Muller's muscle, these fibers hitchhike along the oculomotor nerve, specifically traveling with the fibers that form the superior division of CN III, then reaching Muller's muscle via small branches. That’s why the sympathetic supply to Muller's muscle rides with the superior division of CN III. The inferior division carries other extraocular motor fibers and parasympathetic fibers to the ciliary ganglion, so it’s not the route for Muller's sympathetic input.