View source for Muscular layer

{{Short description|Layer of many organs in vertebrates}}
{{Infobox anatomy
| Name        = Muscular layer
| Latin       = tunica muscularis
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| Image       = Gray1134.png
| Caption     = [[Histology|Histological]] section of the [[ureter]], showing the thick muscular layers surrounding the [[Lumen (anatomy)|lumen]].
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{{Gastrointestinal wall series}}
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.

==Structure==
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. Stomach contains an additional oblique muscle layer just interior to circular muscle 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]].

In the [[Large intestine|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.

==Function==
The muscularis layer is responsible for the [[Peristalsis|peristaltic movements]] and   [[Segmentation contractions|segmental contractions]] in and the [[alimentary canal]]. The [[Myenteric plexus|Auerbach's nerve plexus]] (myenteric nerve plexus) is found between longitudinal and circular muscle layers, it starts muscle contractions to initiate [[peristalsis]].

==References==
{{Gray's}}
{{Reflist}}

==External links==
* {{BiowebUW|/APlab/Lab-Unit-14/lab-14-28.html|Muscularis externa of the colon}}
* {{BiowebUW|/APlab/Lab-Unit-11/Lab-11-07.html|Smooth muscle layers of the gut}}
* {{UIUCHistologySubject|23}}
* {{BUHistology|11601ooa}}&nbsp;— "Muscle Tissue: smooth muscle, muscularis externa"

{{Digestive tract}}
{{Urinary system anatomy}}
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[[Category:Membrane biology]]