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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. [3] [4] [5] [6]
Onuf's nucleus is the origin of innervation for the striated muscles of the rectum and urethral sphincters.The neurons of Onuf's nucleus are responsible for controlling external sphincter muscles of the anus and urethra in humans.
The inferior rectal nerves (inferior anal nerves, inferior hemorrhoidal nerve) usually branch from the pudendal nerve but occasionally arises directly from the sacral plexus; they cross the ischiorectal fossa along with the inferior rectal artery and veins, toward the anal canal and the lower end of the rectum, and is distributed to the sphincter ani externus (external anal sphincter, EAS) and ...
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 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 .
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.
The nerves that compose the cauda equina innervate the pelvic organs and lower limbs to include motor innervation of the hips, knees, ankles, feet, internal anal sphincter and external anal sphincter. In addition, the cauda equina extends to sensory innervation of the perineum and, partially, parasympathetic innervation of the bladder. [1]
The middle fibers are inserted into the side of the rectum, blending with the fibers of the sphincter muscles; lastly in the male, the anterior fibers descend upon the side of the prostate to unite beneath it with the muscle of the opposite side, joining with the fibers of the external anal sphincter and transverse perineal muscles, at the ...