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The female or male external sphincter muscle of urethra (sphincter urethrae): located in the deep perineal pouch, at the bladder's distal inferior end in females, and inferior to the prostate (at the level of the membranous urethra) in males. It is a secondary sphincter to control the flow of urine through the urethra.
The external sphincter muscle prevents urine leakage as the muscle is tonically contracted via somatic fibers that originate in Onuf's nucleus and pass through sacral spinal nerves S2-S4 then the pudendal nerve to synapse on the muscle. [1] [2] Voiding urine begins with voluntary relaxation of the external urethral sphincter.
At the root of the penis (the proximal end of the corpus spongiosum) lies the external sphincter muscle. This is a small sphincter of striated muscle tissue and is in healthy males, under voluntary control. Relaxing the urethral sphincter allows the urine in the upper urethra to enter the penis properly and thus empty the urinary bladder.
The external urethral sphincter is a striated muscle that allows voluntary control over urination. [5] The internal sphincter, formed by the involuntary smooth muscles lining the bladder neck and urethra, receives its nerve supply by the sympathetic division of the autonomic nervous system. [6] The internal sphincter is present both in males ...
The human urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, control levels of electrolytes and metabolites , and regulate blood pH .
The internal urethral sphincter is a urethral sphincter muscle which constricts the internal urethral orifice. It is located at the junction of the urethra with the urinary bladder and is continuous with the detrusor muscle , [ 1 ] [ 2 ] but anatomically and functionally fully independent from it. [ 3 ]
A rhabdosphincter (from Greek rhabdos meaning "rod") is a sphincter consisting of striated muscle fibres. [1] The muscle is a part of the external urethral sphincter that continues superiorly as a trough-like extension running vertically across the anterior aspect of the prostate to reach the neck of the bladder. [2] [3]
Diagram of ileocaecal valve and sphincter. The sphincter pupillae, or pupillary sphincter, belonging to the iris in the eye. The orbicularis oculi muscle, a muscle around the eye. The upper oesophageal sphincters; The lower esophageal sphincter, or cardiac sphincter, at the upper portion of the stomach.