Crayfish escape behavior

Abstract

1. Intracellular recordings were made from the somata of central neurons in semi-intact preparations in order to trace sensory pathways in the phasic extensor system. 2. The tonic and phasic muscle receptor organs (MROs or stretch-receptors) produce unitary EPSPs in the phasic extensor motoneurons (Figs. 1, 2). 3. The tonic MRO also produces large, unitary EPSPs in the peripheral inhibitor to the phasic flexors (FI); smaller EPSPs are produced by the phasic MRO (Fig. 2). 4. The MRO-produced EPSPs in FI can summate with central excitation to fire FI (Fig. 3). The EPSPs appear to be monosynaptic and chemical, and show slight posttetanic potentiation (Fig. 5). 5. Each MRO distributes excitation to at least 3 ganglia, but EPSPs in the ganglion where the axon enters are several times larger than EPSPs in neighboring ganglia. The connections made by the MROs are highly specific — the MROs do not contact the fast flexor motoneurons or extensor inhibitors (Figs. 6, 7, 8). 6. The MROs appear to be the exclusive source of monosynaptic sensory input to the extensor motoneurons, but excitation via polysynaptic pathways can be produced by stimulating any sensory root in the abdomen (Fig. 9). Polysynaptic excitation peaks at about 30 ms, which is close to the time when the extensors should fire during the tail flip.