A Muscle That Controls the Diameter of an Opening Is

Question

A muscle that controls the diameter of an opening is a ________ muscle.
A)parallel
B)convergent
C)pennate
D)bipennate
E)circular

Accepted Answer

A circular muscle, also known as a sphincter, is responsible for controlling the diameter of an opening by contracting and relaxing in a circular fashion. Examples of circular muscles include the sphincter muscles of the digestive and urinary systems.