Physiological Basis of Electrogastrography

Abstract

In this chapter, the anatomical, functional, and in vivo myoelectrical characteristics of the normal stomach are reviewed. The anatomical regions of the stomach are shown in Figure 3.1. Major areas are the fundus, the body (corpus), antrum, and pyloroduodenal area. Extrinsic innervation of the stomach is provided by the vagus nerve and splanchnic nerves. The pacemaker region is shown on the greater curvature of the stomach between the fundus and the corpus. From the pacemaker region, spontaneous electrical depolarization and repolarization occurs and generates the myoelectrical waves that are termed the gastric pacesetter potentials, or slow waves. The prominent muscle layers of the stomach are the circular and the longitudinal muscle layers (see Fig. 3.1, middle). The oblique muscle layer is included in the muscularis. Between these smooth muscle layers lie the neurons of the myenteric plexus, the gastric components of the enteric nervous system. Afferent neurons, interneurons, and postganglionic parasympathetic neurons all have synaptic interactions in the myenteric plexus. Intrinsic neurons and extrinsic excitatory and inhibitory neurons from the vagus nerve and splanchnic nerves, intraluminal contents, and hormones modulate contraction and relaxation of the smooth muscle in the different regions of the stomach. Important anatomical and functional relationships exist among the circular smooth muscle layer, the myenteric neurons, and the interstitial cells of Cajal (ICCs) (see Fig. 3.1, bottom). The ICCs are the pacemaker cells, the cells that spontaneously depolarize and repolarize and set the myoelectrical rhythmicity of the stomach and other areas of the gastrointestinal tract. The interstitial cells are electrically coupled with the circular muscle cells. Low-amplitude rhythmic circular contractions occur at the pacemaker rhythm. Rhythmicity and contractility of the circular muscle layer are modulated by ongoing activity excitatory and inhibitory of myenteric neurons that synapse with the interstitial cells. The interstitial cells have a variety of other receptors. Electrocontractile activities of the gastric smooth muscle are modified by neuronal and hormonal inputs appropriate for fasting and specific postprandial conditions. Control of rhythmicity may be modulated by a variety of stimuli that affect the interstitial cells and is a focus of intense investigation.