Figure 2. Components of the peristaltic reflex and relationship to enteric and extrinsic neural control.

In the peristaltic reflex, distension of the intestine by a bolus is sensed by the intrinsic primary afferent neurons, which stimulate interneurons to activate ascending contraction proximal to the bolus through excitatory neurons. Stimulation of muscles occurs through effects of transmitters such as acetyl choline and neurokinins such as substance P and substance K. The intrinsic primary afferent neuron also stimulates descending inhibition in the receiving segment of the intestine distal to the bolus, and this effect is mediated by inhibitory transmitters, such as VIP and nitric oxide (NO).