The circular muscle of the iris
A) contracts in response to bright light to produce pupillary constriction
B) is innervated by the parasympathetic nervous system
C) contracts to slacken the suspensory ligaments and to increase the strength of the lens during accommodation
D) contracts in response to bright light to produce pupillary constriction and is innervated by the parasympathetic nervous system
E) all of these

Question

Quizplus · Accepted Answer

The circular muscle of the iris contracts in response to bright light to produce pupillary constriction, which is an important reflex to protect the retina from excessive light. This muscle is innervated by the parasympathetic nervous system, which releases acetylcholine to stimulate contraction. However, the muscle does not have any direct impact on the suspensory ligaments or the lens during accommodation, which is mainly controlled by the ciliary muscle and its zonular fibers. Therefore, only option D is correct.

The Circular Muscle of the Iris