Sphincter ani externus muscle

Sphincter ani externus muscle

Muscle infobox
Name = Sphincter ani externus muscle
Latin = musculus sphincter ani externus
GraySubject = 120
GrayPage = 425


Caption =


Caption2 = Coronal section through the anal canal. B. Cavity of urinary bladder V.D. Ductus deferens. S.V. Seminal vesicle. R. Second part of rectum. A.C. Anal canal. L.A. Levator ani. I.S. Sphincter ani internus. E.S. Sphinear ani externus.
Origin =
Insertion =
Action = keep the anal canal and orifice closed
Blood =
Nerve = branch from the fourth sacral and twigs from the inferior hemorrhoidal branch of the pudendal nerve
MeshName =
MeshNumber =
DorlandsPre = m_22
DorlandsSuf = 12550801
The Sphincter ani externus (external anal sphincter) is a flat plane of muscular fibers, elliptical in shape and intimately adherent to the integument surrounding the margin of the anus.

Anatomy

It measures about 8 to 10 cm in length, from its anterior to its posterior extremity, and is about 2.5 cm broad opposite the anus.

It consists of two strata, superficial and deep.

* The "superficial", constituting the main portion of the muscle, arises from a narrow tendinous band, the anococcygeal raphé, which stretches from the tip of the coccyx to the posterior margin of the anus; it forms two flattened planes of muscular tissue, which encircle the anus and meet in front to be inserted into the central tendinous point of the perineum, joining with the Transversus perinæi superficialis, the Levator ani, and the Bulbocavernosus.

* The "deeper" portion forms a complete sphincter to the anal canal. Its fibers surround the canal, closely applied to the Sphincter ani internus, and in front blend with the other muscles at the central point of the perineum.

In a considerable proportion of cases the fibers decussate in front of the anus, and are continuous with the Transversi perinæi superficiales.

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.

Actions

The action of this muscle is peculiar.

(1) It is, like other muscles, always in a state of tonic contraction, and having no antagonistic muscle it keeps the anal canal and orifice closed.

(2) It can be put into a condition of greater contraction under the influence of the will, so as more firmly to occlude the anal aperture, in expiratory efforts unconnected with defecation.

(3) Taking its fixed point at the coccyx, it helps to fix the central point of the perineum, so that the Bulbocavernosus may act from this fixed point.

Pathology

Anismus is a paradoxical contraction of the external anal sphincter, when the intent is relaxation, which can result in obstructed defecation and constipation. Abnormal function of this muscle is also seen in anorectal malformation and after certain surgeries, including coccygectomy.


=Additional

ee also

*Puborectalis muscle

External links

*
* - "The Male Perineum and the Penis: The External Anal Sphincter"
* (NormanAnatomyFig|analtriangle3)
* (NormanAnatomyFig|rectum)


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Look at other dictionaries:

  • Sphincter ani internus muscle — Muscle infobox Name = Sphincter ani internus muscle Latin = musculus sphincter ani internus GraySubject = 120 GrayPage = 426 Caption = Coronal section through the anal canal. B. Cavity of urinary bladder V.D. Ductus deferens. S.V. Seminal vesicle …   Wikipedia

  • Sphincter ani — can refer to: * Sphincter ani externus muscle * Sphincter ani internus muscle …   Wikipedia

  • musculus sphincter ani externus — noun an external ring of striated muscle surrounding the anus • Hypernyms: ↑skeletal muscle, ↑striated muscle • Part Holonyms: ↑anal sphincter, ↑sphincter ani, ↑musculus sphincter ani …   Useful english dictionary

  • sphincter ani — noun the sphincter muscle of the anus • Syn: ↑anal sphincter, ↑musculus sphincter ani • Hypernyms: ↑sphincter, ↑anatomical sphincter, ↑sphincter muscle • Part Holonyms: ↑ …   Useful english dictionary

  • musculus sphincter ani — noun the sphincter muscle of the anus • Syn: ↑anal sphincter, ↑sphincter ani • Hypernyms: ↑sphincter, ↑anatomical sphincter, ↑sphincter muscle • Part Holonyms: ↑anus …   Useful english dictionary

  • sphincter muscle — ▪ anatomy  any of the ringlike muscles surrounding and able to contract or close a bodily passage or opening. One of the most important human sphincter muscles is the sphincter pylori, a thickening of the middle layer of stomach muscle around the …   Universalium

  • sphincter muscle of anus external — musculus sphincter ani externus …   Medical dictionary

  • Anal sphincter muscles — can refer to:* Sphincter ani externus muscle * Sphincter ani internus muscle …   Wikipedia

  • sphincter — A muscle that encircles a duct, tube, or orifice in such a way that its contraction constricts the lumen or orifice. SYN: musculus s. [TA], s. muscle [TA]. [G. sphinkter, a band or lace] s. of ampulla s. of hepatopancreatic ampulla. anatomic s.… …   Medical dictionary

  • Muscle — is the tissue of the body which primarily functions as a source of power. There are three types of muscle in the body. Muscle which is responsible for moving extremities and external areas of the body is called "skeletal muscle." Heart… …   Medical dictionary

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