Urethral Sphincter

The term urethral sphincter refers to one of two muscles used to control the exit of urine in the urinary bladder through the urethra. The two muscles are the external urethral sphincter and the internal urethral sphincter. When either of these muscles contract, the urethra is sealed shut.

The external urethral sphincter originates at the ischiopubic ramus and inserts into the intermeshing muscle fibers from the other side. It is controlled by the deep perineal branch of the pudendal nerve. Activity in the nerve fibers constricts the urethra.

  • The internal sphincter muscle of urethra: located at the bladder's inferior end and the urethra's proximal end at the junction of the urethra with the urinary bladder. The internal sphincter is a continuation of the detrusor muscle and is made of smooth muscle, therefore it is under involuntary or autonomic control. This is the primary muscle for prohibiting the release of urine.
  • The external sphincter muscle of urethra (sphincter urethrae): located at the bladder's distal inferior end in females and inferior to the prostate (at the level of the membranous urethra) in males is a secondary sphincter to control the flow of urine through the urethra. Unlike the internal sphincter muscle, the external sphincter is made of skeletal muscle, therefore it is under voluntary control of the somatic nervous system.

Read more about Urethral SphincterSex Differences, Function

Other articles related to "sphincter, urethral sphincter, sphincters":

Urination - Physiology
... is low, resulting in excitation of the outlet (the sphincter and urethra), and relaxation of the bladder ... During the storage phase the internal urethral sphincter remains tense and the detrusor muscle relaxed by sympathetic stimulation ... muscle to contract and the internal urethral sphincter to relax ...
Urethral Sphincter - Function
... In addition to the internal and external sphincters, in males the urethra extends to the end of the penis, where it opens up to the outside ... this muscle may be damaged, most commonly by childbirth, leading to weakness of the sphincter mechanism and stress incontinence ...
Sphincter Urethrae
... The term urethral sphincter refers to one of two muscles used to control the exit of urine in the urinary bladder through the urethra ... The two muscles are the external urethral sphincter and the internal urethral sphincter ... The external urethral sphincter originates at the ischiopubic ramus and inserts into the intermeshing muscle fibers from the other side ...
Pittle - Anatomy and Physiology - Physiology
... resulting in excitation of the outlet (the sphincter and urethra), and relaxation of the bladder ... During the storage phase the internal urethral sphincter remains tense and the detrusor muscle relaxed by sympathetic stimulation ... stimulation causes the detrusor muscle to contract and the internal urethral sphincter to relax ...