What is a characteristic of the dilator muscle of the iris?

• A. It constricts the pupil
• B. It is innervated by the parasympathetic nervous system
• C. It dilates the pupil
• D. It is the primary muscle for vision

Answer: (C)

The dilator muscle of the iris is specifically responsible for enlarging the pupil, a process known as pupil dilation. This action is primarily regulated by the sympathetic nervous system. When stimulated, the dilator muscle contracts, causing the pupil to widen, which allows more light to enter the eye. This is particularly important in low-light conditions when the eye needs to maximize light intake for better vision.

Understanding the role and function of the dilator muscle is crucial for comprehending how the eye adapts to different lighting conditions. Additionally, the other options each describe different functions and characteristics that do not align with that of the dilator muscle, highlighting its specific purpose in the mechanics of the iris and pupil.