Reflex Control of Abdominal Flexor Muscles in the Crayfish: I. The Twitch System

Abstract

ABSTRACT The polyneuronal innervation of crustacean muscles has been well explored in decapod limbs, both comparatively at the level of entire muscles (Wiersma & Ripley, 1952) and, by means of single motor axon stimulation and microelectrode recording, at the level of single muscle fibres (Fatt & Katz, 1953 a, b; Furshpan, 1955; Hoyle & Wiersma, 1958). Experiments of the latter sort have shown that motor axons produce excitatory junctional potentials (e.j.p.s) that may or may not give rise to active electrogenic events (spikes). The e.j.p.s evoked by different motor axons may differ in amplitude, rate of rise or fall, and tendency to facilitate upon repetitive stimulation; axons that evoke more sharply rising e.j.p.s exhibiting little facilitation have been termed ‘fast’, and others ‘slow.’