The Physiology of A Lepidopteran Muscle Receptor

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Abstract
When a single MRO of a caterpillar is stretched at least 32 motor units show clear reflex changes in activity. The great majority of muscles are excited., and the latency of the reflex differs only slightly from one muscle to another. The response has both tonic and phasic components which reflect more or less faithfully the magnitudes of the same components in the sensory discharge. Muscles are affected on the contralateral side of the stimulated segment and on the ipsilateral side of adjacent segments. The reflex fields of neighbouring receptors therefore overlap; spatial facilitation produces a disproportionate increase in the overall response when two receptors are stimulated simultaneously. The reflex pathway for muscles innervated by nerve 2 is shown to involve synaptic connexions in the ganglion of the segment anterior to the stimulated receptor and responding muscles. The muscles most strongly excited are those which he functionally in parallel with a stretched sense organ. It is concluded that a major function of the caterpillar MRO is to mediate a negative feedback reflex tending to stabilize bodily position independent of load.