Role of proprioceptive feedback from nonspiking mechanosensory cells in the sand crab, Emerita analoga.

The two programmes underlying uropod beating in Emerita ('swimming' and 'treading water') are distinguished by a difference in timing of the power stroke within the interval between return strokes (cycle). While 'swimming' (cycles approx. 80-400 ms) the phase and while 'treading water' (cycles approx. 100-700 ms) the latency of the power stroke are relatively invariant. Analyses of electromyograms of untrestrained Emerita, before and after bilateral surgical ablation of the four nonspiking mechanoreceptive cells associated with each uropod, established that power strokes in 'treading water' are dependent upon proprioceptive feedback from the nonspiking cells. As cycle duration increases from 80 to 700 ms, the function of the reafference changes from reinforcement of the centrally generated 'swimming' pattern to production of the 'treading water' pattern.