Nerve Impulse Patterns and Reflex Control in the Motor System of the Crayfish Claw

Open Access
Publisher Website
Google Scholar
Abstract
The opener muscle of the crayfish claw receives, under nearly natural conditions, a train of excitatory nerve impulses which may show a temporal patterning to which the muscle is specially sensitive. Especially at high frequencies the impulse train contains doublets which form a separate class in the interval distribution. Their appearance at high frequencies gives rise to an increase in the coefficient of variation of interval lengths. Excitatory and inhibitory motor neurons to the same opener muscle seem to be part of the same commonly excited motor neuron pool. Frequency changes in the two axons generally show positive correlations. For most inputs and for ‘spontaneous’ central drive the excitor has the lowest threshold and shortest latency, and it gives the earliest indication of changes of excitatory state. Proprioceptive input from the claw may excite both motor neurons, but generally the inhibitory one gives the earlier, bigger response. The peripheral inhibition completes a negative feedback loop. Inhibitory frequencies plotted against concurrent excitatory frequencies give points falling into two groups with different slopes dependent upon input source. For general body inputs the slope is less than one and for proprioceptive claw input it is much more than one. This divergence leads to greater effectiveness of either excitation or inhibition as overall level of output increases, with a good separation of antagonistic functions in spite of the apparent lack of reciprocal interaction.