Mixing and moving in the gut

The motility of the gastrointestinal tract consists of local, non-propulsiv e mixing (pendular or segmental) and propulsive (peristaltic) movements. It is generally considered that mixing movements are produced by intrinsic pa cemakers which generate rhythmic contractions, and peristalsis by intrinsic excitatory and inhibitory neural reflex pathways, but the relationship bet ween mixing and peristalsis is poorly understood. Peristalsis is compromise d in mice lacking interstitial cells of Cajal, suggesting that these pacema ker cells may also be involved in neural reflexes. Here we show that mixing movements within longitudinal muscle result from spontaneously generated w aves of elevated internal calcium concentration which originate from discre te locations (pacing sites), spread with anisotropic conduction velocities in all directions, and terminate by colliding with each other or with adjac ent neurally suppressed regions. Excitatory neural reflexes control the spr ead of excitability by inducing new pacing sites and enhancing the overall frequency of pacing, whereas inhibitory reflexes suppress the ability of ca lcium waves to propagate. We provide evidence that the enteric nervous syst em organizes mixing movements to generate peristalsis, linking the neural r egulation of pacemakers to both types of gut motility.