Frequency gradients of the basic electrical and mechanical rhythms along the rat intestine.
The basic mechanical rhythm (BMR), initiated and maintained by the basic electrical rhythm (BER), ensures the muscular tonus of the intestine during the interdigestive phases. The frequency and amplitude gradient for the BER waves and, correlated with them, the frequency and size gradient of the BMR contraction force have an anatomic determination. The circular muscle layer is discontinuous, consisting of cylindrical segments separated by conjunctive tissue, segments whose size increases starting from the duodenum to the ileocecal valve. The electrical connection between the cylindrical segments formed by the circular muscles is provided by the layer of longitudinal muscle fibres. Each and every segment generates a general voltage which is higher than that of the preceeding segment, so that the slow BER wave becomes amplified along the intestine. In correlation with the electrical phenomena, the BMR contractile waves will become more ample in the terminal region of the intestine, facilitating the progress through peristalsis of the luminal content with greater viscosity.