© 1974 by The Society for Integrative and Comparative Biology
Neural Control of Swimming in the Leech
Department of Molecular Biology, University of California Berkeley, California 94720
Leeches swim by undulating; they alternately form crests then troughs at their anterior end and move Them backward, thereby producing forward thrust. These movements are accomplished by alternating contractions of dorsal and ventral longitudinal muscles in each of the 21 body segments. These contractions are caused by bursts of impulses in groups of excitatory and inhibitory motor neurons. Connections among motor neurons help to coordinate these bursts: synergistic muscle excitors are electrotonically coupled, which aids in keeping their bursts nearly synchronous; muscle inhibitors also inhibit the excitors to the same muscles, and it is this inhibition which keeps the excitors from being tonically active during swimming. Neurons sensitive to either dorsal or ventral body wall stretch produce reciprocal stretch reflexes to the muscle excitors, probably via the inhibitors. That these stretch reflexes may be involved in generating the periodic bursts is supported by the results of both behavioral and electrophysiological experiments.