The muscular layer (muscular coat, muscular fibers, muscularis propria, muscularis externa) is a region of

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

in many organs in the vertebrate body, adjacent to the

submucosa The submucosa (or tela submucosa) is a thin layer of tissue (biology), tissue in various organ (anatomy), organs of the gastrointestinal tract, gastrointestinal, respiratory tract, respiratory, and genitourinary system, genitourinary tracts. It i ...

. It is responsible for gut movement such as

peristalsis Peristalsis ( , ) is a radially symmetrical contraction and relaxation of muscles that propagate in a wave down a tube, in an anterograde direction. Peristalsis is progression of coordinated contraction of involuntary circular muscles, which ...

. The Latin, tunica muscularis, may also be used.

Structure

It usually has two layers of

smooth muscle Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...

: * inner and "circular" * outer and "longitudinal" However, there are some exceptions to this pattern. * In the

stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...

there are three layers to the muscular layer. Stomach contains an additional oblique muscle layer just interior to circular muscle layer. * In the upper

esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...

, part of the externa is ''

skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

'', rather than smooth muscle. * In the

vas deferens The vas deferens or ductus deferens is part of the male reproductive system of many vertebrates. The ducts transport sperm from the epididymis to the ejaculatory ducts in anticipation of ejaculation. The vas deferens is a partially coiled tube ...

of the spermatic cord, there are three layers: inner longitudinal, middle circular, and outer longitudinal. * In the

ureter The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In a human adult, the ureters are usually long and around in diameter. The ureter is lined by urothelial cells, a type of transitional epit ...

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 A sphincter is a circular muscle that normally maintains constriction of a natural body passage or orifice and which relaxes as required by normal physiological functioning. Sphincters are found in many animals. There are over 60 types in the hum ...

at two locations of the

gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organ (biology), organs of the digestive syste ...

: * in the

pylorus The pylorus ( or ), or pyloric part, connects the stomach to the duodenum. The pylorus is considered as having two parts, the ''pyloric antrum'' (opening to the body of the stomach) and the ''pyloric canal'' (opening to the duodenum). The ''pylori ...

of the

, it forms the

pyloric sphincter The pylorus ( or ), or pyloric part, connects the stomach to the duodenum. The pylorus is considered as having two parts, the ''pyloric antrum'' (opening to the body of the stomach) and the ''pyloric canal'' (opening to the duodenum). The ''pylori ...

. * in the

anal canal The anal canal is the part that connects the rectum to the anus, located below the level of the pelvic diaphragm. It is located within the anal triangle of the perineum, between the right and left ischioanal fossa. As the final functional seg ...

, it forms the internal anal sphincter. In the colon, the fibres of the external longitudinal smooth muscle layer are collected into three longitudinal bands, the

teniae coli The taeniae coli (also teniae coli or tenia coli) are three separate longitudinal ribbons (''taeniae'' meaning ribbon in Latin) of smooth muscle on the outside of the ascending, transverse, descending and sigmoid colons. They are visible and can b ...

. The thickest muscularis layer is found in the

(triple layered) and thus maximum peristalsis occurs in the stomach. Thinnest muscularis layer in the alimentary canal is found in the

rectum The rectum is the final straight portion of the large intestine in humans and some other mammals, and the Gastrointestinal tract, gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the s ...

, where minimum peristalsis occurs.

Function

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

References

External links

* * * * — "Muscle Tissue: smooth muscle, muscularis externa" {{Authority control Membrane biology