Phase Setting and Locomotion

Abstract

The nematode Ascaris suum has been the object of intensive study by the group working under the direction of Antony Stretton at Madison and there is an extensive picture of the motorneuronal types of synapses in the worm, as well as the neural architecture (see Stretton, 1978, 1985 for further references). However, the way that the elements in the circuit combine to produce motion is not understood. The present report examines the viability of a mechanism for control of locomotion. Ascaris has approximately 300 neurons and, of these, 80 or so, including interneurons, control locomotion. The neural architecture can be thought of as consisting of five repetitions of a basic pattern of eleven motor neurons, some excitatory and some inhibitory. There is a dorsal nerve cord and a ventral nerve cord, which synapse onto dorsal and ventral muscle cells, respectively. Here we focus on the propagation of a wave in a single chain of muscles which could represent either the dorsal or ventral chain, and do not address the question of coordination of the two cords.