The Exoskeleton and Insect Proprioception

Abstract

ABSTRACT In the cockroach tibia, the activities of campaniform sensilla that monitor cuticular strain have been recorded in free-walking animals. In walking, sensillum firing is correlated with myographic activity of the flexor and extensor tibiae muscles. The specific activity of a single campaniform sensillum depends upon the orientation of its cuticular cap. In slow walking, proximal sensilla, whose ovoid cuticular caps are oriented perpendicular to the leg long axis, fire in bursts that are initiated just prior to the onset of extensor tibiae activity in the stance phase of locomotion. The firing frequency within bursts of proximal sensilla is generally inversely related to the frequency of the slow extensor tibiae motoneurone and ceases when motoneurone activity exceeds 200 Hz. Distal campaniform sensilla, oriented parallel to the leg long axis, only fire when slow extensor tibiae activity exceeds 300 Hz. In slow walking, distal sensillum activity typically occurs as a short intense burst near the end of the stance phase of the step cycle, when slow extensor frequency is maximal. Distal sensillum firing is greatly increased when forward progression is impeded. The patterns of afferent activity seen in slow walking indicate that the campaniform sensilla function in load compensation and limitation of muscle tensions. The proximal sensilla respond to initial loading of the leg and can reflexly excite the slow extensor motoneurone in compensation. The distal sensilla respond to cuticular strains that result from large extensor contractions and can reflexly inhibit the slow motoneurone. In rapid walking, activities of both subgroups of campaniform sensilla shift in phase relative to slow extensor firing. Proximal sensilla activity occurs after the onset of slow extensor firing. Distal sensilla bursts follow the termination of slow extensor activity. These phase shifts limit the reflex functions of the tibial campaniform sensilla in rapid walking. Shifts in phase of afferent activity may contribute to the need for central programming of locomotion.