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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]
The internal anal sphincter, IAS, or sphincter ani internus is a ring of smooth muscle that surrounds about 2.5–4.0 cm of the anal canal. It is about 5 mm thick, and is formed by an aggregation of the smooth (involuntary) circular muscle fibers of the rectum. [citation needed]
Anatomy of the human anus. Frontal section. The anus is the final part of the gastrointestinal tract, and directly continues from the rectum, passing through the pelvic floor. The top and bottom of the anus are surrounded by the internal and external anal sphincters, two muscular rings which control defecation.
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 sphincter urethrae, or urethral sphincter, controlling the exit of urine from the body. At the anus, there are two anal sphincters which control the exit of feces from the body, the internal anal sphincter and external anal sphincter. The inner sphincter is involuntary and the outer is voluntary.
The anal triangle is the posterior part of the perineum. ... Sphincter ani externus muscle; ... perineum at The Anatomy Lesson by Wesley Norman ...
Anal sphincter muscles may refer to: External anal sphincter; Internal anal sphincter This page was last edited on 2 January 2025, at 16:44 (UTC). Text is ...
The anocutaneous line is slightly below the pectinate line and a landmark for the intermuscular border between internal and external anal sphincter muscles. The anocutaneous line represents the transition point from non-keratinized stratified squamous epithelium of the anal canal to keratinized stratified squamous epithelium of the anus and ...