Crayfish escape behavior

Summary

• 1. Intracellular recordings from neuronal somata and extracellular recordings from peripheral nerves were used to study the effects of impulses in the giant escape command interneurons upon the extensor systems in the crayfish abdomen.

• 2. Extensor motoneurons are inhibited by command cell impulses. Inhibitory postsynaptic potentials (IPSPs) occur in the phasic motoneurons at short latency and last for 20–30 ms. IPSPs also occur, but less reliably, following antidromic stimulation of the fast flexor motoneurons (Figs. 1, 2).

• 3. The peripheral inhibitors to both the phasic and tonic extensor muscles are excited by command cell impulses; a single command cell impulse can produce a burst of impulses in the inhibitors (Figs. 3–5).

• 4. The largest ‘accessory’ neuron or peripheral inhibitor of the muscle receptor organ (MRO) is also excited by the escape command cells (Fig. 6).

• 5. The durations of IPSPs in the phasic extensor motoneurons, MROs, and phasic extensor muscles are all less than half as long as IPSPs in flexor elements. Thus, they are short enough to permit the extensors to be activated at the termination of the flexion phase (Fig. 7).

• 6. No evidence was obtained in isolated cords for rebound from inhibition or delayed excitation of extensor motoneurons. The exclusive effect of a command impulse upon the extensor systems is inhibition. Inhibition occurs centrally, and peripherally at sensory elements and muscles.