The femoral chordotonal organ of the stick insect Cuniculina impigra was stimulated by moving its apodeme with staircase-like waveforms having independently controllable acceleration and velocity values. Intracellular recordings were made of receptor units in the sensory nerve. Apart from receptors encoding position and velocity (see preceding paper, Hofmann, Koch & Bässler, 1985) specific acceleration receptors and also receptors responding to both the acceleration and the velocity of the stimulus could be distinguished. The pure acceleration receptors fall into two categories: units reacting only to one sign of acceleration (e.g. onset of relaxation and end of elongation) and units reacting to both signs of accelerations. Individual thresholds for each sign of acceleration were measured and analysed. Latencies of the receptors were determined and found to be dependent on the degree of acceleration.
A possible role for the acceleration receptors in an alarm system of the animal is discussed.