FIGURE 2.

The colonic motor complex (CMC) at different levels of excitation. In this and all subsequent figures, black identifies contraction, and white relaxation or distention; the top of all figures is the proximal part of the colon. (A) Upon mild excitation by increased intraluminal pressure, proximal rhythmic (pacemaker) activity appear in the colon always starting in the most proximal pacemaker activity. These are usually rhythmic, and almost always start in the proximal colon to propagate a short distance. (B) Fast propagating contractions (FPCs). Further excitation may elicit a CMC, which is always rhythmic and triggered by proximal activity. The weakest form of CMCs presented as single FPCs, clustered-FPCs or a mix of short contractions that together form a complex of pan-colonic activity. (C) Long distance contractions (LDCs). Full-blown LDCs are shown here, which are manifestations of CMCs at their highest level of excitation. (D) This figure shows how proximal rhythmic contractions can develop from proximal activity to eventually trigger LDCs. (E) This figure shows how proximal activity can occur rhythmically and at a high frequency where only every 3rd or 5th activity triggers an LDC. (F) “Broken” long distance contractions. The CMC can show many compositions in between low-amplitude FPCs and full-blown LDCs. Here we see many LDCs we have previously identified as “broken LDCs” (Chen et al., 2013), where it appears that the LDC is interrupted by one or many streaks of inhibition.