Final answer:
Mydriasis is pupil dilation, while myosis is pupil constriction. The sympathetic system causes pupil dilation, and the parasympathetic system causes pupil constriction. Therefore, the correct option is a. Pupil dilation vs. pupil constriction.
Step-by-step explanation:
Mydriasis is pupil dilation, while myosis is pupil constriction. When the sympathetic system is activated, norepinephrine binds to adrenergic receptors in the radial fibers of the iris smooth muscle, causing pupil dilation. On the other hand, the parasympathetic system releases acetylcholine onto circular fibers in the iris, resulting in pupil constriction. Therefore, the correct option is a. Pupil dilation vs. pupil constriction.