The musculature and innervation of the alimentary canal

Abstract

The alimentary canal is traditionally divided into two basic parts, the esophagus and the gastrointestinal tract. As is well known, both portions are composed of four concentric layers: the mucosa, lined by epithelial cells, contains a supporting layer of connective tissue, the lamina propria, and the muscularis mucosae, which is present in most but not all of the alimentary canal; the submucosa, a second layer of loose connective tissue; the tunica muscularis, which is smooth muscle throughout the digestive tube, except for the sup-perior one-third of the esophagus, which contains striated muscle; and the serosa which is the most external of the four layers. The tunica muscularis, in turn, is divided into an inner band of circular muscle and an outer band of longitudinal muscle. Thus, muscle is actually located in two areas of the canal wall, the muscularis mucosae and the tunica muscularis (1,2).