Final answer:
The sympathetic system causes dilated pupils (mydriasis), while the parasympathetic system causes constricted pupils (miosis). The afferent branch of dilation is the sensory input through the optic nerve, and the efferent branch is the motor response carried by the sympathetic nervous system. An example of pupil dilation is entering a dark room.
Step-by-step explanation:
In the autonomic control of pupillary size, the sympathetic system causes dilated pupils (mydriasis) while the parasympathetic system causes constricted pupils (miosis). Norepinephrine is responsible for dilation, whereas acetylcholine is responsible for constriction of the pupil.
When light hits the retina, the sensory input travels through the optic nerve as the afferent branch. The motor response to the ciliary ganglion and iris, which leads to dilation, is carried by the efferent branch of the sympathetic nervous system.
Example: If you enter a dark room, your pupils will dilate in response to the low light levels, allowing more light to enter your eyes.