Figure 1  .

Extrinsic and intrinsic control of gastrointestinal motility. The extrinsic sympathetic and parasympathetic supply to the gut modulates the function of the enteric brain located in ganglionated plexi along the gastrointestinal tract. Transmitters released from the enteric neurons, which are the intrinsic neural control of the gut, modulate the peristaltic reflex. The major transmitters in the peristaltic reflex are shown on the right, acetylcholine (ACh) and substance P (SubP) are the predominant excitatory neurotransmitters, and vasoactive intestinal polypeptide (VIP) and nitric oxide are the predominant inhibitory neurotransmitters. SubK, substance K; NOS, nitric oxide synthase. (Reproduced with permission, Ann Rev Med 1999 (in press).)