What is the muscularis in the digestive tract?

• A. The layer responsible for motility in the digestive tract
• B. The innermost layer
• C. The layer containing blood vessels and nerves
• D. The outermost layer

Answer: (A)

Motility of the digestive tract is driven by the muscularis externa, the layer of smooth muscle that contracts to move and mix contents. It has an inner circular layer and an outer longitudinal layer, and its activity is coordinated by the enteric nervous system, including the myenteric (Auerbach) plexus situated between these muscle layers. The mucosa is the innermost lining involved in secretion and absorption; the submucosa contains blood vessels, nerves, and glands; the outermost layer is the serosa (or adventitia). Because this layer powers peristalsis and segmentation, it is the correct choice.