Final answer:
The dilator pupillae (radial muscles) are responsible for dilating the pupils of the eyes, allowing more light to enter in low light conditions. They are contrasted by the sphincter pupillae (circular muscles), which constrict the pupil in bright light.
Step-by-step explanation:
The dilator pupillae (radial muscles) are responsible for dilating the pupils of the eyes. These muscles extend radially from the edge of the pupil to the outer rim of the iris and contract in low light conditions, widening the pupil to allow more light to enter the eye. This action is opposed by the sphincter pupillae (circular muscles), which contract in bright light to constrict the pupil and reduce light entry. The dilator pupillae is controlled by the sympathetic nervous system, while the sphincter pupillae are controlled by the parasympathetic nervous system.
Other muscles like the medial rectus and inferior oblique are involved in eye movement, but not pupil size. The medial rectus muscle turns the eye inward towards the nose, while the inferior oblique muscle helps to rotate the eye.