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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]
This results in less smooth muscle contraction of the colon, increasing the colon transit time. [12] The reduced dopamine levels also causes dystonia of the striated muscles of the pelvic floor and external anal sphincter. This explains how Parkinson's disease can lead to constipation. [14]
In females, there is no union, nor a tendinous perineal raphe; the parts are disjoint primarily and arise from the same central tendinous point of the perineum, which is the tendon that is formed at the point where the bulbospongiosus muscle, superficial transverse perineal muscle, and external anal sphincter muscle converge to form this major ...
Kegel exercises can train the perineal muscles by increasing the oxygen supply and the strength of those muscles. [19] The names of the perineal muscles are: ischiocavernosus (erection), bulbocavernosus (ejaculation), external sphincter of the anus, striated urethral sphincter, transverse perineal, levator of the prostate, and puborectalis. [20]
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. Movement of the feces is also controlled by the involuntarily controlled internal anal sphincter ...
The pelvic floor are the muscles that attach to the pelvis in the abdomen. Anal sphincter dyssynergia can be caused by obstructions, but mostly improper relaxing of the anal sphincters or pelvic floor muscle during defecation. Also if there is a decrease in intrarectal pressure defecation can occur. [5]
The conjoint longitudinal muscle is a muscle layer in the wall of the anal canal between the internal anal sphincter (deep to CLM) and external anal sphincter (superficial to CLM). It is continuous proximally with the longitudinal (outer) smooth muscle layer of the rectum. It receives autonomic innervation in common with the internal anal ...
The external anal sphincter, by contrast, is made up of skeletal (or striated muscle) and is therefore under voluntary control. It can contract vigorously for a short time. Contraction of the external sphincter can defer defecation for a time by pushing stool from the anal canal back into the rectum.