An anal sphincter is a group of muscles at the end of the rectum that surrounds the anus and controls the release of stool, thereby maintaining continence. There are two sphincter muscles: one is internal and one is external. The external muscle helps maintain continence and keep stool in the rectum. If there is a loss of muscle control in the sphincter, incontinence may occur. The inner muscle is not under voluntary control but rather is controlled by the autonomic nervous system.
The external anal sphincter or sphincter ani externus is a flat plane of skeletal muscle fibers, elliptical in shape and intimately adherent to the skin surrounding the margin of the anus. In a considerable proportion of cases the fibers decussate in front of the anus, and are continuous with the superficial transverse perineal muscle. Posteriorly, they are not attached to the coccyx, but are continuous with those of the opposite side behind the anal canal. The upper edge of the muscle is ill-defined, since fibers are given off from it to join the levator ani. The action of this muscle is peculiar.
Medically reviewed by Drugs. Last updated on May 13, When stool feces leaks out from the rectum accidentally, it is known as fecal incontinence. Under normal circumstances, stool enters the end portion of the large intestine, called the rectum, where it is temporarily stored until a bowel movement occurs.
Jump to navigation. A sphincter injury refers to a tear or damage to the muscle that surrounds the anal canal. These muscles are used to control bowel movements. Damage to one or both of these muscles can result in the decreased ability to control bowel movements and can contribute to symptoms of accidental bowel leakage.