Theexternal anal sphincter(orsphincter ani externus) is an oval tube ofskeletal muscle fibers.[1]Distally, it is adherent to theskinsurrounding the margin of theanus.[2]It exhibits a resting state of tonical contraction[1]and also contracts during thebulbospongiosus reflex.[3][4][5][6]
| External anal sphincter | |
|---|---|
 | |
 Coronal section through theanal canal.B. Cavity ofurinary bladderV.D.Ductus deferens.S.V.Seminal vesicle.R. Second part ofrectum.A.C. Anal canal. L.A.Levator ani.I.S.Sphincter ani internus.E.S.Sphincter ani externus. | |
| Details | |
| Nerve | Branch from the fourth sacral and contributions from the inferior hemorrhoidal branch of thepudendal nerve |
| Actions | Keep theanal canalandorificeclosed |
| Identifiers | |
| Latin | sphincter ani externus |
| TA98 | A04.5.04.012 |
| TA2 | 2426 |
| FMA | 21930 |
| Anatomical terms of muscle | |
Anatomy
editThe external anal sphincter is far more substantial than the internal anal sphincter. The proximal portion of external anal sphincter overlaps the internal anal sphincter (which terminates distally a little distance proximal to the anal orifice) superficially; where the two overlap, they are separated by the interveningconjoint longitudinal muscle.[1]
Structure
editHistorically, the sphincter was described as consisting of three parts (deep, superficial, and subcontinuous). This is not supported by current anatomical knowledge. Some sources still describe it in two layers, deep (or proximal) and superficial (or distal or subcutaneous).[1]
Some of the muscles fibres decussate at the anterior midline and posterior midline, so forming an anterior commissure and posterior commissure.[1]
Attachments
editThis sectionneeds expansion.You can help byadding to it.(July 2023) |
The muscle attaches anteriorly onto theperineal body,and posteriorly onto the anococcygeal ligament.[1]
Innervation
editThe sphincter receives innervation from the bilaterally pairedinferior anal nerve(each a branch of thepudendal nervewhich is derived from ventral rami of S2-S4). It may also receive additional motor innervation from thenerve to levator ani.[1]
Histology
editThe sphincter consists mostly ofslow twitch fibersthat allow extended continuous contraction.[1]
Gallery
edit-
Intestines -
Anatomy of the human anus. -
Muscles of male perineum. -
Muscles of the female perineum. -
Sagittal (vertical) section of bladder, penis, and urethra.
See also
editReferences
edit- ^abcdefghStandring, Susan (1201).Gray's Anatomy: The Anatomical Basis of Clinical Practice(42th ed.). New York. p. 683.ISBN978-0-7020-7707-4.OCLC1201341621.
- ^Gray, Henry (1918).Gray's Anatomy(20th ed.). pp. 424–425.
- ^Vodušek DB, Deletis V (2002). "Intraoperative Neurophysiological Monitoring of the Sacral Nervous System".Neurophysiology in Neurosurgery, A Modern Intraoperative Approach:153–165.doi:10.1016/B978-012209036-3/50011-1.ISBN9780122090363.S2CID78605592.
- ^Sarica Y, Karacan I (July 1987). "Bulbocavernosus reflex to somatic and visceral nerve stimulation in normal subjects and in diabetics with erectile impotence".The Journal of Urology.138(1): 55–58.doi:10.1016/S0022-5347(17)42987-9.PMID3599220.
- ^Jiang XZ, Zhou CK, Guo LH, Chen J, Wang HQ, Zhang DQ, et al. (December 2009). "[Role of bulbocavernosus reflex to stimulation of prostatic urethra in pathologic mechanism of primary premature ejaculation]".Zhonghua Yi Xue Za Zhi(in Chinese).89(46): 3249–3252.PMID20193361.
- ^Podnar S (February 2012). "Clinical elicitation of the penilo-cavernosus reflex in circumcised men".BJU International.109(4): 582–585.doi:10.1111/j.1464-410X.2011.10364.x.PMID21883821.S2CID27143105.
This article incorporates text in thepublic domainfrompage 425of the 20th edition ofGray's Anatomy(1918)
External links
edit- Anatomy photo:42:13-0100at the SUNY Downstate Medical Center - "The Male Perineum and the Penis: The External Anal Sphincter"
- perineumat The Anatomy Lesson by Wesley Norman (Georgetown University) (analtriangle3)
- pelvisat The Anatomy Lesson by Wesley Norman (Georgetown University) (rectum)
