Abstract
An earlier proposed model of the de-efferented muscle spindle mechano-receptors has been developed further to simulate the effects of the dynamic fusimotor (γ D) activation of the group Ia afferents (primary endings).
The rate sensitivity of the original second order receptor model might be increased simply by increasing the overall viscous damping of the simulated polar regions of the nuclear bag fibre. However, adequate simulation of the typical time course of the stretch response of the primary endings during γ D-activation required a subdivision of the polar regions into an active and a passive part. A reasonable behaviour of the model was obtained by simulating a local contraction covering about 50–90% of the polar regions of the nuclear bag fibres.
The ramp response of the model showed a “quick” rate response component that increased by increasing the rate of the simulated stretch. This component was not significantly influenced by the simulated γ D-activation.
A “slow” rate component appeared to increase approximately in the same proportion as the intensity of the simulated γ D-activation.
The behaviour of the model closely corresponds to that of the biological prototype. The study demonstrates that the electrophysiological effects of activating the dynamic fusimotor fibres are indeed compatible with peripheral mechanical events associated with contraction phenomena within the polar regions of the nuclear bag intrafusal muscle fibres.
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Rudjord, T. Model study of muscle spindle primary endings subjected to dynamic fusimotor activation. Kybernetik 11, 148–153 (1972). https://doi.org/10.1007/BF00270671
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DOI: https://doi.org/10.1007/BF00270671