Ciliary Ganglion

Dilation of the pupil, mydriasis, occurs due to postganglionic sympathetic innervation from the superior cervical ganglion. Preganglionic fibers arise from the neurons first and second thoracic intermediolateral column and by the upper thoracic spinal nerves, and white rami communicantes reach the superior cervical ganglion. From there, they traverse the long ciliary nerves to the dilator pupillae. Pupils also dilate in response to pain, presumably due to fibers from the sensory system reaching the preganglionic neurons (pupillary skin reflex).

ACCOMMODATION REFLEX

In viewing objects that are near, the pupils constrict, the eyes move medially, and the lens changes shape to become more convex. The reflex for this begins in the retina, and then involves the optic nerve, optic tract, lateral geniculate bodies, optic radiations, and visual cortical centers. From there, the impulse is thought to reach the “near response neurons” in the pretectal nuclei by corticotectal fibers. From the pretectal nuclei, the information reaches the oculomotor nuclei. The parasympathetic fibers reach the sphincter pupillae via the ciliary ganglion and short ciliary nerves. The parasympathetic fibers cause stimulation of the ciliary muscles, which causes relaxation of the zonule, and the lens becomes more spheric; the medial recti are activated by the ventral oculomotor nuclei, causing the eyes to converge.

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