Gastrointestinal Wall Figure 62-2 shows a typical cross section of the intestinal wall, including the following layers
from outer surface inward: (1) the serosa, (2) a longitudinal smooth muscle layer, (3) a circular smooth muscle layer, (4) the submucosa, and (5) the mucosa. In addition, sparse bundles of smooth
muscle fibers, the mucosal muscle, lie in The deeper layers of the mucosa.
Gastrointestinal Smooth Muscle
The smooth muscle of the gastrointestinal tract is excited by
almost continual slow, intrinsic electrical activity along the membranes of the muscle fibers. This
activity has two basic types of electrical waves: (1) slow waves and (2) spikes, both of which are
shown in Figure 62-3. In addition, the voltage of the resting membrane potential of the gastrointestinal
smooth muscle can be made to change to different levels, and this, too, can have important effects in
controlling motor activity of the gastrointestinal tract.
