Tuning posture to body load: decreases in load produce discrete sensory signals in the legs of freely standing cockroaches |
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Authors: | Bridget R Keller Elizabeth R Duke Ayman S Amer Sasha N Zill |
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Institution: | (1) Department of Anatomy and Pathology, Joan C. Edwards School of Medicine, Marshall University, Huntington, WV 25704, USA |
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Abstract: | Decreases in load are important cues in the control of posture and walking. We recorded activities of the tibial campaniform
sensilla, receptors that monitor forces as strains in the exoskeleton, in the middle legs of freely moving cockroaches. Small
magnets were attached to the thorax and body load was changed by applying currents to a coil below the substrate. Body position
was monitored by video recording. The tibial sensilla are organized into proximal and distal subgroups that have different
response properties and reflex effects: proximal sensilla excite extensor motoneurons while distal receptors inhibit extensor
firing. Sudden load decreases elicited bursts from distal sensilla, while increased load excited proximal receptors. The onset
of sensory discharges closely approximated the time of peak velocity of body movement in both load decreases and increases.
Firing of distal sensilla rapidly adapted to sustained unloading, while proximal sensilla discharged tonically to load increases.
Load decreases of small amplitude or at low rates produced only inhibition of proximal activity while decrements of larger
size or rate elicited distal firing. These response properties may provide discrete signals that either modulate excitatory
extensor drive during small load variations or inhibit support prior to compensatory stepping or initiation of swing. |
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Keywords: | Force Insect Mechanoreception Unloading Posture |
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