Längsmuskelschicht

Längsmuskelschicht, or longitudinal muscle layer, is one of the two main muscle coats of the muscularis externa in many hollow organs, consisting of smooth muscle cells arranged along the length of the organ. It lies outside the inner circular layer and together with it forms the muscularis externa that governs gut motility.

In the gastrointestinal tract, the longitudinal layer runs around the circumference of the organ and, in the colon, thickened regions form the teniae coli, three distinct longitudinal bands. The relative thickness and arrangement of the longitudinal layer can vary along different segments, contributing to region-specific motility patterns. Besides the GI tract, similar longitudinal smooth muscle layers are found in other tubular organs involved in propulsion and constriction.

Functionally, the longitudinal layer works in concert with the inner circular layer to produce coordinated movements such as peristalsis and segmentation. Contraction of the longitudinal layer shortens and lengthens a gut segment, while the circular layer constricts the lumen; together these actions generate propulsion and mixing of contents.

Nervous control is provided by the enteric nervous system, particularly the myenteric (Auerbach) plexus situated between the circular and longitudinal layers. This plexus regulates the rhythmic contractions and tone of the muscularis externa, with parasympathetic activity generally enhancing motility and sympathetic activity often inhibiting it. Abnormal function of these layers can contribute to motility disorders.