Figure 1.

Simplified organization of the gut-brain axis. The main anatomical and functional subdivisions of a mammalian gut-brain axis are represented with neurons belonging to the enteric and extrinsic autonomic systems in different colors. Importantly, the enteric nervous system is entirely contained within the gastrointestinal wall. For purposes of simplification, all the nerve branches supplying the gut, pancreatic post-ganglionic neurons and the sacral parasympathetic system are not depicted in this figure.