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The muscular layer (muscular coat, muscular fibers, muscularis propria, muscularis externa) is a region of muscle in many organs in the vertebrate body, adjacent to the submucosa. It is responsible for gut movement such as peristalsis. The Latin, tunica muscularis, may also be used.
It usually has two layers of smooth muscle:
However, there are some exceptions to this pattern.
The inner layer of the muscularis externa forms a sphincter at two locations of the gastrointestinal tract:
In the colon, the fibres of the external longitudinal smooth muscle layer are collected into three longitudinal bands, the teniae coli.
The thickest muscularis layer is found in the stomach (triple layered) and thus maximum peristalsis occurs in the stomach. Thinnest muscularis layer in the alimentary canal is found in the rectum, where minimum peristalsis occurs.
The muscularis layer is responsible for the peristaltic movements and segmental contractions in and the alimentary canal. The Auerbach's nerve plexus (myenteric nerve plexus) is found between longitudinal and circular muscle layers, it starts muscle contractions to initiate peristalsis.