Adaptive reconfiguration of a reflex circuit during different motor programmes in the locust |
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Authors: | T Jellema W J Heitler |
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Institution: | (1) The Gatty Marine Laboratory, University of St. Andrews, St. Andrews, Fife KY16 8LB, Scotland, Tel.: +44-1334/463489, Fax: +44-1334/463443, e-mail: tj@st-and.ac.uk, GB |
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Abstract: | The cuticle strain which develops in the hindleg tibiae when a locust prepares to kick, or when the tibia thrusts against
an obstacle, is detected by two campaniform sensilla, which reflexly excite the fast extensor tibiae motoneuron, some of the
flexor tibiae motoneurons and nonspiking interneurons. The reflex excitation is adaptive for the extensor motoneuron during
both co-activation and thrusting, but is only adaptive for the flexor motoneurons during co-activation, and is maladaptive
during thrusting. We show that the femoral chordotonal organ, which monitors tibial position, controls the efficacy of the
strain feedback. The campaniform sensilla-induced depolarization in the extensor motoneuron is about twice as large when the
tendon is in mid position (reflecting a tibial-femoral angle of 90°) than when fully stretched (reflecting tibial flexion),
while in the flexors the reverse is true. The amplitudes of excitatory postsynaptic potentials evoked by single campaniform
sensilla spikes, are, however, not affected. Our data suggests that the chordotonal organ modulates the gain of the strain
feedback onto the motoneurons by exciting interneuronal circuits whose output sums with the former. Thrusting typically occurs
with the tibia partially extended, therefore the actions of the chordotonal organ support the production of a maximal thrusting
force.
Accepted: 27 December 1996 |
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Keywords: | Grasshopper Schistocerca gregaria Campaniform sensilla Proprioceptor Kicking |
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