Final answer:
Pupillary dilation, or mydriasis, is the expansion of the pupil. It can be caused by the sympathetic nervous system or substances like phenylephrine. Although dilation can occur in various situations, it may not always signal a problem.
Step-by-step explanation:
Pupillary dilation, also known as mydriasis, is a physiological response that occurs when the pupil of the eye expands. This is often caused by the activation of the sympathetic nervous system. When certain substances, such as drugs or eye drops that contain dilating agents like phenylephrine, are applied to the eye, they can also cause pupillary dilation.
For example, phenylephrine acts by binding to adrenergic receptors in the radial fibers of the iris smooth muscle, mimicking the action of norepinephrine. By doing so, it triggers the muscles responsible for pupil dilation to contract, resulting in a wider opening of the pupil.
It's important to note that while pupillary dilation can be caused by the sympathetic nervous system and certain substances, it's not always an indication of a specific condition or problem. Sometimes it can occur as a normal response to different stimuli.