Phasic organization of the migrating motility complex

The article presents some old and new data regarding organization of the migrating motility complex (MMC) and its phases. The MMC cycle is one of two main motility patterns present in the gastrointestinal tract of humans and animals. The MMC is composed of three or four phases numbered consecutively. Both generation and organization of the cycle are still incompletely understood. Any progress in this area can help in further recognition of mechanisms of pattern generation and arrival what is of clinical importance since many MMC disturbances are observed. Thus the article presents some old and new data further explaining the role of phase 3 of the cycle and suggesting revised MMC organization. Its inactive phase is commonly labeled as phase 1 of the MMC, implying that the entire MMC pattern is initiated just during this phase. Irregular phase 2 could represent the spontaneous activity. The highly propulsive and specific phase 3 of the MMC commences in the course of phase 2b and apparently is embedded in this phase. Phase 3 is thus often considered the most characteristics and important in the cycle and it can be assumed that the triggering of phase 3 of the MMC initiates the appearance of the whole MMC cycle, at least when a given locus is considered. Phase 4 of the MMC, also irregular and thus similar to the phase 2, may represent the terminal part of phase 2. Therefore the numbering of the classical phases 1, 2a, 2b, 3 and 4 as phases 2, 3a, 3b, 1, and 3c, respectively seems more relevant. It is believed that presented view of the MMC organization will help in a better understanding of the character of the cycle.