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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]
Stress urinary incontinence is a common problem related to the function of the urethral sphincter. Weak pelvic floor muscles, intrinsic sphincter damage, or damage to the surrounding nerves and tissue can make the urethral sphincter incompetent, and subsequently it will not close fully, leading to stress urinary incontinence.
The pelvic splanchnic nerves contribute to the innervation of the pelvic and genital organs. [2] The nerves regulate the emptying of the urinary bladder, control opening and closing of the internal urethral sphincter, influence motility in the rectum as well as sexual functions like erection. [1] [2]
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 internal anal sphincter, IAS, or sphincter ani internus is a ring of smooth muscle that surrounds about 2.5–4.0 cm of the anal canal. It is about 5 mm thick, and is formed by an aggregation of the smooth (involuntary) circular muscle fibers of the rectum.
The pudendal nerve is the main nerve of the perineum. [1]: 274 It is a mixed (motor and sensory) nerve and also conveys sympathetic autonomic fibers.It carries sensation from the external genitalia of both sexes and the skin around the anus and perineum, as well as the motor supply to various pelvic muscles, including the male or female external urethral sphincter and the external anal sphincter.
Stimulation of the parasympathetic will cause the detrusor muscle (urinary bladder wall) to contract and simultaneously relax the internal sphincter muscle between the bladder and the urethra, allowing the bladder to void. Also, parasympathetic stimulation of the internal anal sphincter will relax this muscle to allow defecation.
The detrusor muscle, also detrusor urinae muscle, muscularis propria of the urinary bladder and (less precise) muscularis propria, is smooth muscle found in the wall of the bladder. The detrusor muscle remains relaxed to allow the bladder to store urine , and contracts during urination to release urine.