Numerical simulation of motility patterns of the small bowel. 1. Formulation of a mathematical model

A complete mathematical model of the periodic myoelectrical activity of a f unctional unit of the small intestine is presented. Based on real morpholog ical and electrophysiological data, the model assumes that: the functional unit is an electromyogenic syncytium; the kinetics of L-type Ca2+, T-type C a2+, Ca2+-activated K+, voltage dependent K+ and Cl- channels determine the electrical activity of the functional unit; the enteric nervous system is satisfactorily represented by an efferent cholinergic neuron that provides an excitatory input to the functional unit through receptor-linked L-type C a2+ channels and by an afferent pathway composed of the primary and the sec ondary sensory neurons; the dynamics of propagation of the wave of depolari zation along the unmyelinated nerve axons satisfy the Hodgkin-Huxley model; the electrical activity of the neural soma reflects the interaction of N-t ype Ca2+ channels, Ca2+-activated K+ and voltage dependent Na+, K+ and Cl- channels; the smooth muscle syncytium of the locus is a null-dimensional co ntractile system. With the proposed model the dynamics of active force gene ration are determined entirely by the concentration of cytosolic calcium. T he model describes: the mechanical excitation of the free nerve endings of the mechanoreceptor of the receptive field of the pathway; the electrical p rocesses of the propagation of excitation along the afferent and efferent n eural circuits; the chemical mechanisms of nerve-pulse transmission at the synaptic zones; the slow wave and bursting type electrical activity; cytoso lic calcium concentration; the dynamics of active force generation. Numeric al simulations have shown that the model can display different electrical p atterns and mechanical responses of the locus. The results show good qualit ative and quantitative agreement with the results of experiments conducted on the small intestine. (C) 1999 Academic Press.