Figure 1.

The enteric nervous system and its glial components

(A) The human alimentary tract extending from the esophagus to the rectum contains an intrinsic network of neuro-glial circuits termed the enteric nervous system (ENS).

(B) The bowel is visualized in cross-section (here the small intestine) to illustrate the location of the two major enteric plexuses in relation to the laminar structure of the bowel. The larger plexus, the myenteric plexus, is located in between the outer longitudinal and inner circular layers of the muscularis propria. The smaller submucosal plexus is situated in the submucosa, in between the mucosa and the muscularis propria.

(C) Schematic of higher magnification view of small bowel cross-section illustrating that while neuronal cell bodies are largely restricted to the enteric plexuses (gray), enteric glial cells (EGCs) are distributed more widely across all the lamina. Mucosal EGCs (Type III), located closest to the intestinal lumen, are multipolar with long branches. Intraganglionic EGCs (Type I), located within both the submucosal and myenteric plexuses, are extensively branched. EGCs within nerve fibers that connect ganglia of the same type are elongated and less extensively branched (Type II), and intramuscular EGCs located along small nerve fibers in the muscle layers are bipolar in morphology (Type IV). Glia have been detected in all layers of the human bowel wall, and while the morphological subtypes shown here have been established in rodent models, emerging evidence supports similar morphologies in humans.