Mechanical responses of the body wall muscle of the earthworm, Lumbricus terrestris, to segmental nerve stimulation

Abstract

Suitable nerve–muscle preparations are described for recording the electrical and mechanical responses of the longitudinal and circular muscle to segmental nerve stimulation in the earthworm, Lumbricus terrestris. The longitudinal muscle response to prolonged repetitive stimulation consists of a smooth increase in tension to form a peak in less than 10 s followed by a slow decline in tension to about one-half peak tension in 45 s. The circular muscle response to prolonged repetitive stimulation consists of two distinct phases of tension development: an initial, rapidly developing peak resembling that in longitudinal muscle and a slow, irregularly developing second phase. The circular and longitudinal muscle responses are obtained at frequencies above f or 2/s, with the amplitude of each response being a function of the stimulus strength within a range of 0.4–1.4 V (2 ms) and the stimulus frequency within a range of 5–50/s. In addition there is a threshold-dependent inhibition of the second phase of the circular muscle response.Circular and longitudinal responses to single stimuli are obtained with stimulus strengths approximately 10 times greater than those of the responses to repetitive stimulation and the amplitude of these responses appears to be a function of the strength of stimulation. The single stimulus response appears to be a result of repetitive firing in the same motor fibers which mediate the response to repetitive stimulation.