THE LOCUST ABDOMINAL MUSCLE RECEPTOR ORGAN - RESPONSE CHARACTERISTICSAND ITS ROLE IN THE CONTROL OF SEGMENTAL DISTANCE

A single mutipolar receptor cell is located at the dorsal edge of the lateral internal dorsal muscle in each abdominal segment of the locust (Locusta migratoria). Muscle and receptor cell form the abdominal mus cle receptor organ. The receptor cell monitors length changes in the i ntersegmental muscle, and as a consequence also detects the length of an abdominal segment (cuticule and intersegmental membrane). The muscl e receptor organ responds in a phasictonic fashion. The phasic compone nt encodes the rate of change in the stimulus independent from the pre vailing length of the muscle receptor organ. The tonic component monit ors the absolute length of the muscle. Stimulation of a single muscle receptor organ leads to reflex effects on the ipsilateral longitudinal muscles in at least three adjacent segments. Muscles that shorten the abdomen are activated while their extending antagonists receive reduc ed activity. The reflex activation of the muscles is polysynaptic. Mon osynaptic connections between the receptor and the motoneurones were n ot found. We identified an interneurone that receives monosynaptic inp ut from the muscle receptor organs in at least three adjacent segments . The interneurone excites motorneurones to the longitudinal muscles o f the next posterior segment.