What is a sphincter muscle?

1 Answer
Jul 14, 2017

A sphincter muscle is a circular muscle that controls the opening of a passage.

Explanation:

Sphincter muscles are circular muscles found in various body passages or openings. They control the opening and closing of that passage or opening.

Sphincter muscles can be voluntary (e.g. the external urethral sphincter) or involuntary. (e.g. the internal urethral and the internal anal sphincters) .