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The anus is surrounded by a group of muscles called the anal sphincter, which controls the release of stool. The anal sphincter consists of two muscles: the internal anal sphincter and the external anal sphincter. The external anal sphincter is an oval tube of skeletal muscle fibres that attaches to the skin surrounding the anus. The internal anal sphincter can become narrowed in a condition called anal stenosis, which makes it difficult to have a bowel movement. The anal sphincter can also be affected by conditions such as Crohn's disease and anorectal malformations.
| Characteristics | Values |
|---|---|
| Does the anus have muscles? | Yes, the anal sphincter is a group of muscles at the end of the rectum. |
| Number of muscles | Two: the internal anal sphincter and the external anal sphincter. |
| Location | The anal sphincter surrounds the anus. |
| Function | The anal sphincter controls the release of stool. |
| Conditions | The anal sphincter may be damaged if you have trouble holding in stool and/or urine, or if you have pain in your rectum. |
| Innervation | The sphincter receives innervation from the bilaterally paired inferior anal nerve (each a branch of the pudendal nerve which is derived from ventral rami of S2-S4). |
| Muscle fibres | The external anal sphincter is an oval tube of skeletal muscle fibres. |
| Muscle contraction | The external anal sphincter exhibits a resting state of tonical contraction and also contracts during the bulbospongiosus reflex. |
| Relative size | The external anal sphincter is far more substantial than the internal anal sphincter. |
| Overlap | The proximal portion of the external anal sphincter overlaps the internal anal sphincter. |
| Historical description | The sphincter was historically described as consisting of three parts: deep, superficial, and subcutaneous. |
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What You'll Learn
- The anal sphincter is a group of muscles at the end of the rectum
- The rectum is located at the last few inches of the large intestine (colon)
- The anal sphincter surrounds the anus and controls the release of stool
- There are two muscles: the internal anal sphincter and the external anal sphincter
- The external anal sphincter is far more substantial than the internal anal sphincter
The anal sphincter is a group of muscles at the end of the rectum
The anal sphincter may be damaged if you have trouble holding in stool and/or urine (or it leaks out) or if you have pain in your rectum. Anal fissures may be treated with topical medications, medications that help relax the sphincter muscle, or surgery. Anismus is a functional disorder of the pelvic floor muscles, including the external anal sphincter. It is caused by a problem with the way these muscles contract and relax during defecation. Anal stenosis is a condition in which the internal anal sphincter becomes narrowed to the point where it is difficult to have a bowel movement.
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The rectum is located at the last few inches of the large intestine (colon)
The anal sphincter muscles may be damaged if you have trouble holding in stool and/or urine, or if you experience rectal pain. Anal fissures, a condition that causes pain and bleeding, can be treated with topical medications, medications that relax the sphincter muscle, or surgery. Anismus, a functional disorder of the pelvic floor muscles, can also affect the external anal sphincter. It is caused by a problem with the way these muscles contract and relax during defecation.
Anorectal malformations are a type of birth defect that causes the anus to develop abnormally. They can affect the sphincter and/or other parts of the rectum and anus. Surgery is required to correct these malformations. Crohn's disease, which can affect any part of the digestive tract, can also impact the anal sphincter. It is estimated that around one-third of patients with Crohn's disease will experience complications in the perianal area.
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The anal sphincter surrounds the anus and controls the release of stool
The anus is surrounded by a group of muscles called the anal sphincter, which controls the release of stool. There are two muscles that make up the anal sphincter: the internal anal sphincter and the external anal sphincter. The external anal sphincter is an oval tube of skeletal muscle fibres that attaches to the skin surrounding the anus. It is far more substantial than the internal anal sphincter, which is located a little further inside the body. The two muscles overlap, separated by the conjoint longitudinal muscle.
The anal sphincter is responsible for maintaining continence. If the anal sphincter is damaged, a person may experience difficulty holding in stool and/or urine, or they may feel pain in their rectum. Anal fissures, which can be caused by surgery, laxative overuse, or infections, may also affect the anal sphincter. They can be treated with topical medications, medications that relax the sphincter muscle, or surgery.
Another condition that can affect the anal sphincter is anismus, a functional disorder of the pelvic floor muscles, including the external anal sphincter. Anismus is caused by a problem with the way these muscles contract and relax during defecation and is often treated with pelvic floor exercises.
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There are two muscles: the internal anal sphincter and the external anal sphincter
The anus does have muscles. The anal sphincter is a group of muscles at the end of the rectum, which is located at the last few inches of the large intestine (colon). The anal sphincter surrounds the anus and controls the release of stool, thereby maintaining continence.
The internal anal sphincter can become narrowed to the point where it is difficult to have a bowel movement, a condition known as anal stenosis. Anal stenosis can occur after surgery, especially haemorrhoid removal, or be associated with laxative overuse or infections. The external anal sphincter can be affected by anismus, a functional disorder of the pelvic floor muscles caused by a problem with the way these muscles contract and relax during defecation.
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The external anal sphincter is far more substantial than the internal anal sphincter
The anus has two muscles: the internal anal sphincter and the external anal sphincter. The external anal sphincter is far more substantial than the internal anal sphincter. It is an oval tube of skeletal muscle fibres that attaches anteriorly onto the perineal body and posteriorly onto the anococcygeal ligament. The muscle receives innervation from the bilaterally paired inferior anal nerve, which is a branch of the pudendal nerve. It may also receive additional motor innervation from the nerve to levator ani. The external anal sphincter consists mostly of slow twitch fibres that allow extended continuous contraction.
The proximal portion of the external anal sphincter overlaps the internal anal sphincter superficially. Where the two overlap, they are separated by the intervening conjoint longitudinal muscle. Historically, the sphincter was described as consisting of three parts: deep, superficial, and subcutaneous.
The anal sphincter muscles may be damaged if you have trouble holding in stool and/or urine or if you have pain in your rectum. Anal fissures may be treated with topical medications, medications that help relax the sphincter muscle, or surgery. Anismus is a functional disorder of the pelvic floor muscles, including the external anal sphincter. It is caused by a problem with the way these muscles contract and relax during defecation.
Frequently asked questions
Yes, the anus has muscles. The anal sphincter is a group of muscles at the end of the rectum.
The internal and external anal sphincters are two muscles that surround the anus and control the release of stool. The external anal sphincter is an oval tube of skeletal muscle fibres, while the internal anal sphincter is smaller and located a little further from the anal orifice.
If the anal sphincter is damaged, it can cause trouble holding in stool and/or urine, or pain in the rectum.
Anal stenosis is a condition where the internal anal sphincter becomes narrowed, making it difficult to have a bowel movement. It can be caused by surgery, especially hemorrhoid removal, or be associated with laxative overuse or infections.
Anismus is a functional disorder of the pelvic floor muscles, including the external anal sphincter. It is caused by a problem with the way these muscles contract and relax during defecation.
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