The gastrointestinal tract has a self-contained, 'enteric', nervous system within its walls. These are drawn as solid and dashed lines on the inner side of the GI tract. The central nervous system also plays a role in the tract's motility and secretions. Stimulatory nerves are shown as solid orange lines and inhibitory nerves are dashed orange lines.
The right illustration depicts the role of this system in the motility of the stomach. Nerves embedded in the stomach wall (drawn along the inner stomach wall) relay impulses from stretch receptors in the stomach wall (top small square) to surrounding muscles. These impulses increase the motility of the stomach when food is present. These same receptors also send stimulatory nerve signals to the central nervous system (CNS square) that returns stimulatory nerve signals to the muscles of the stomach wall to reinforce motility.
When food leaves the stomach and enters the small intestine, stretch receptors in that location (lower small square) send inhibitory nerve signals (dashed blunt-end line) back up to the stomach muscles. This decreases gastric motility until food moves further down the small intestine. Hydrogen ion receptors ( small square) operate by the same mechanism and have the same effect on gastric motility. This interplay between the small intesting and the stomach is often referred to as the 'intestinal phase' of gastric activity.
The left illustration depicts the role of the central nervous system (CNS square) in initiating the secretion of 'gastric juice'. This is often referred to as the 'cephalic phase' of gastric activity. Stimulatory nerves, represented as solid blunt-end lines, innervate chief (zymogenic) cells and parietal cells that line the gastric pits in the upper regions of the stomach. They are illustrated in the map as labeled circles. The solid-headed dashed arrows that lead from these circles indicates they are secreting their products into the stomach.
Last update: 7/19/2005