INTERACTIONS AMONG AN ENSEMBLE OF CHORDOTONAL ORGAN RECEPTORS AND MOTOR NEURONS OF THE CRAYFISH CLAW

Action potentials of crayfish propodite-dactyl (PD) chordotonal organ receptors and two claw motor neurons, the opener inhibitor (OI) and slow closer excitor (CE) were simultaneously monitored during imposed step and ramp movements of the dactyl or while the dactyl was held at various positions. The activities of the cells during imposed displacements were analyzed using peristimulus time histograms and response and contour planes. The proprioceptive fields (PFs) of individual receptors resemble components of the more complex motor neuron PFs. Some receptors are briefly active after each successive opening step, while others do not respond to steps near the closed position but respond as the joint angle increases, becoming active when the claw is held open. Another type of receptor responds to closing movements. Interactions among the various types of receptors and the two motor neurons were detected and analyzed by various statistical methods and intracellular recording techniques. The results indicate that receptors activated during opening movements and when the dactyl is held at open positions excite OI and CE via divergent functional connections. The efficacies of the connections made by a receptor may differ. Receptors activated by closing movements produce hyperpolarizing synaptic potentials in both efferents, possibly directly or via interneurons. It is concluded that several types of chordotonal organ receptors form an ensemble of parallel input channels, which modulates the activities of OI and CE and contributes to the generation of the spatial temporal nonuniformities of their proprioceptive reflex responses.