Colonic motor activity.

The colon exhibits three types of contractions: individual phasic (short and long duration), organized groups (MMCs and nonmigrating motor complexes), and ultrapropulsive (giant migrating contractions). The individual phasic contractions and the MMCs and nonmigrating motor complexes produce extensive mixing and kneading of fecal material and slow net distal propulsion. The GMCs produce mass movements and expel feces during defecation. All contractions are controlled by myogenic, neural, and chemical mechanisms. The myogenic mechanisms determine the timing and frequency of contractions and the duration and distance of propagation of contractions. The neurochemical mechanisms determine whether the contractions will occur at a given site.