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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]
The external anal sphincter can be relaxed by the application of glyceryl trinitrate creams, and constipation is managed with laxatives and improving hydration. [9] Some fissures may require botulinum toxin injection; worst cases may require surgical intervention, such as "lateral internal anal sphincterotomy or advancement anoplasty ...
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 sphincter has a plethora of nerve endings— specifically, the pudendal nerve that branches to supply the external anal sphincter also branches to the dorsal nerve of the clitoris and the ...
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 ...
In humans, the anal canal is approximately 2.5 to 4 cm (0.98 to 1.57 in) long, from the anorectal junction to the anus. [2] [3] [4] It is directed downwards and backwards.. It is surrounded by inner involuntary and outer voluntary sphincters which keep the lumen closed in the form of an anteroposterior sl
The superficial branches supply sensation to the perineum, and the scrotum in men or the labia majora in women. [1] The deep branch supplies superficial transverse perineal muscle, the bulbospongiosus muscle, the ischiocavernosus muscle, the bulb of penis, levator ani, and the external anal sphincter. [1]
In some cases, the fibers of the deeper layer of the external anal sphincter cross over in front of the anus and are continued into this muscle. Occasionally it gives off fibers, which join with the bulbocavernosus of the same side. There are some variations: it may be absent or double, or insert into the bulbocavernosus or the external sphincter.