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The external anal sphincter (or sphincter ani externus) is an oval tube of skeletal muscle fibers. [1] Distally, it is adherent to the skin surrounding the margin of the anus . [ 2 ] It exhibits a resting state of tonical contraction [ 1 ] and also contracts during the bulbospongiosus reflex .
The pudendal nerve that branches to supply the external anal sphincter also branches to the dorsal nerve of the clitoris and the dorsal nerve of the penis. [14] In addition to nerve endings, pleasure from anal intercourse may be aided by the close proximity between the anus and the prostate for males, and vagina, clitoral legs and anal area for ...
The sphincter urethrae, or urethral sphincter, controlling the exit of urine from the body. At the anus, there are two anal sphincters which control the exit of feces from the body, the internal anal sphincter and external anal sphincter. The inner sphincter is involuntary and the outer is voluntary.
The external anal sphincter muscle is the voluntary muscle that surrounds and adheres to the anus at the lower margin of the anal canal. This muscle is in a state of tonic contraction , but during defecation , it relaxes to allow the release of feces .
It is an important anatomical landmark in humans, and forms the boundary between the anal canal and the rectum according to the anatomic definition. [1] Colorectal surgeons instead define the anal canal as the zone from the anal verge to the anorectal ring (palpable structure formed by the external anal sphincter and the puborectalis muscle). [1]
This finding was shown to be absent in healthy subjects, and may be the cause of denervation-related atrophy of the external anal sphincter. Some authors suggest that pudendal nerve damage is the cause for pelvic floor and anal sphincter weakening, and may be the underlying cause of a spectrum of pelvic floor disorders. [5]
It is composed of fibers of the levator ani muscle that unite with the muscle of the opposite side, muscle fibres from external anal sphincter, and fibrous connective tissue. [ 1 ]
The anal wink, anal reflex, perineal reflex, or anocutaneous reflex is the reflexive contraction of the external anal sphincter upon stroking of the skin around the anus. [1] A noxious or tactile stimulus will cause a wink contraction of the anal sphincter muscles and also flexion.