Efferent activity during reflex opening of the crayfish dactylopodite

Abstract

1. Extracellular recording of activity of efferent axons and muscle fibers of the intact crayfish, together with recording of mechanical movements of the claw dactylopodite were used to investigate the activity of inhibitory and motor neurons of the abductor muscle during reflex movement. 2. The action of different receptive zones on the efferent neuron was investigated. During stimulation of some receptive zones there is an increase in activity of the motoneuron and inactivation of the inhibitory neuron; during stimulation of other receptive zones, opening of the dactylopodite takes place with an increase in firing of the motoneuron and it is associated with persistence of activity of the inhibitory neuron. 3. During all forms of afferent stimulation contraction of the abductor muscle of the dactylopodite is determined not only by an increase in the mean frequency of motor spikes, but also by their redistribution into volleys containing 2, 3, or more impulses. Grouping of the spike discharge appears not only in the motor axon (during opening of the claw dactylopodite), but also in the inhibitory axon (during inhibition of the opening reflex). 4. A relationship was found between the amplitude of the muscle potentials and the rate of abduction of the dactylopodite. This relationship is disturbed by activation of the inhibitory neuron. 5. Two components of inhibition (central and peripheral) are used to stop the reflex.