Question

What effect does the sympathetic nervous system exert at the iris?

a) Pupillary constriction
b) Pupillary dilation
c) Blurring of vision
d) Increased tear production

Answer 1

The sympathetic nervous system causes pupillary dilation through the release of norepinephrine, which binds to receptors in the iris.

Step-by-step explanation:

The effect that the sympathetic nervous system exerts at the iris is pupillary dilation. This occurs when norepinephrine, a neurotransmitter released by the sympathetic nervous system, binds to adrenergic receptors on the radial muscle fibers of the iris. The binding of norepinephrine causes these muscles to contract, which leads to the dilation of the pupil. This response is useful in situations requiring heightened alertness or in low light conditions, where a larger pupil allows more light to enter the eye. On the other hand, the parasympathetic nervous system promotes pupillary constriction through the neurotransmitter acetylcholine.