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.
Histological section of the ureter, showing the thick muscular layers surrounding the lumen.
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It usually has two layers of smooth muscle:
- inner and "circular"
- outer and "longitudinal"
However, there are some exceptions to this pattern.
- In the stomach there are three layers to the muscular layer.
- In the upper esophagus, part of the externa is skeletal muscle, rather than smooth muscle.
- In the vas deferens of the spermatic cord, there are three layers: inner longitudinal, middle circular, and outer longitudinal.
- In the ureter the smooth muscle orientation is opposite that of the GI tract. There is an inner longitudinal and an outer circular layer.
The inner layer of the muscularis externa forms a sphincter at two locations of the gastrointestinal tract:
- in the pylorus of the stomach, it forms the pyloric sphincter
- in the anal canal, it forms the internal anal sphincter
This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)
- Muscularis externa of the colon - BioWeb at University of Wisconsin System
- Smooth muscle layers of the gut - BioWeb at University of Wisconsin System
- UIUC Histology Subject 23
- Histology image: 11601ooa – Histology Learning System at Boston University — "Muscle Tissue: smooth muscle, muscularis externa"
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