Question

which of the following controls pupil diameter?
both the parasympathetic and sympathetic nervous systems
neither the parasympathetic nor sympathetic nervous systems
only the parasympathetic nervous system
only the sympathetic nervous system

Explanation:

The parasympathetic nervous system causes pupil constriction (miosis) via the sphincter pupillae muscle. The sympathetic nervous system causes pupil dilation (mydriasis) via the dilator pupillae muscle. So both systems control pupil diameter.

Answer:

both the parasympathetic and sympathetic nervous systems