Final answer:
The sympathetic nervous system causes dilation of the pupils via the release of norepinephrine, which is the correct answer to the question regarding autonomic responses to the head controlled by the sympathetic system.
Step-by-step explanation:
The autonomic responses to the head from the sympathetic control include actions such as sweat, piloerection, blood flow, and elevating the upper eyelid. The correct answer to the question regarding sympathetic control is b. dilate pupils.
Sympathetic nervous system activity leads to pupil dilation, among other responses. This occurs because the sympathetic postganglionic fibers release norepinephrine onto the smooth muscles of the iris, which results in the dilation of the pupils. The opposite effect, constriction of the pupils, is a response of the parasympathetic nervous system, which uses acetylcholine as a neurotransmitter. The sympathetic response enables more light to enter the eye when light levels are low, assisting with vision in dim conditions.