muscle that holds the bladder closed

A ring-like muscle that surrounds the urethra and helps hold it closed, preventing unintentional leakage. When relaxed, a sphincter allows materials such as urine to pass through the opening.21

the muscular structure responsible for opening and closing of the urethra; there are two urethral sphincters - the internal urethral sphincter and the external urethral sphincter.

a striated sphincter muscle that constricts the urethra

Muscle fibers around the outside of the urethra that tighten to close off the flow of urine or relax to open the urethra to allow the passage of urine.