muscularis

Muscularis is a term used in anatomy to refer to the muscular coat of the wall of hollow organs, most commonly the gastrointestinal tract. It comprises two main components: the muscularis mucosae, a thin smooth muscle layer at the boundary between the mucosa and submucosa, and the muscularis externa (also called the muscularis propria), the thicker layer responsible for the major motor movements of the tract.

Muscularis externa is typically organized into two smooth muscle layers: an inner circular layer and an outer longitudinal layer, which in the stomach may include a third oblique layer. Contractions of these layers produce peristalsis, propulsion, and segmentation, helping to move and mix luminal contents.

The muscularis is supplied and regulated by the enteric nervous system. The myenteric (Auerbach) plexus lies between the circular and longitudinal layers and coordinates motility, while the submucosal (Meissner) plexus governs secretory and blood flow aspects of the mucosa. Interstitial cells of Cajal act as pacemaker cells to generate slow rhythmic contractions.

Anatomically, the muscularis lies beneath the submucosa and is bounded externally by either serosa (in intraperitoneal segments) or adventitia (in retroperitoneal segments). The term is often used with the GI tract, but muscularis muscle layers also exist in other hollow organs.

Disorders of muscularis motility, such as achalasia or intestinal pseudo-obstruction, reflect dysfunction of the enteric motor circuitry within this layer.