Final answer:
The pupil is a small opening in the eye that adjusts its size to control the amount of light that enters, responding to different light levels and emotional stimuli. It is controlled by the iris and works in conjunction with the lens to focus light onto the retina, which contains photoreceptors that convert light into nerve signals.
Step-by-step explanation:
The pupil is the small opening in the eye through which light passes. The size of the pupil can change as a function of light levels as well as emotional arousal. When light levels are low, the pupil dilates to allow more light to enter the eye, and when light levels are high, the pupil constricts to reduce the amount of light that enters. This size adjustment is controlled by muscles in the iris, which is the colored part of the eye.
The reception of light by the eye is a critical function for vision. Once the light passes through the pupil, it then enters the lens, which focuses the light onto the retina—the light-sensitive layer of tissue at the back of the eye. The retina contains photoreceptor cells, such as rods and cones, which convert light into nerve impulses. These impulses are then conveyed to the brain by the optic nerve.