Numerical simulation of the gradual reflex of the small bowel

A biomechanical model of the gradual reflex of the small intestine and results of its numerical simulation are presented. It is assumed that the small intestine is composed of longitudinal smooth muscle fibres. Their mechanical activity is under the control of a simple reflex arc represented by a single cholinergic motor neuron. The model describes electromechanical processes of excitation propagation along the reflex arc, chemical mechanisms of nerve-pulse transmission via neuromuscular cholinergic synapse and dynamics of active force generation in the motor unit. Numerical calculation from the model shows that the action potential of amplitude 69 mV propagating along the unmyelinated axon reflex pathway, generates an excitatory postsynaptic potential of amplitude 87 mV at the neuromuscular synapse. The depolarization wave propagates electrotonically along the muscle membrane at a velocity of 1.6 cm/s over the distance of 1.0 cm and initiates the development of a contractile force in the motor unit. Maximum force, equivalent to 19.2 mN occurs in the vicinity of the zone of synaptic contact. After 0.39s the contractile force decreases to 5.8 mN. Comparison of the results calculated using the model are in good agreement with published data from experimental recordings of small bowel longitudinal muscle contraction.