Abstract

AbstractFusimotor activity has been assessed from the changes in the response of muscle spindle receptors to a linear stretch and release of the muscle at various levels of fusimotor drive. The background fusimotor activity of the spinal cat caused an increased dynamic responsiveness of primary endings of ankle flexor as well as the ankle extensor muscles. Further, dynamic activation of both flexor and extensor primary endings was observed during electrical stimulation of the ipsilateral saphenous and the contralateral lateral popliteal nerve. Definite signs of activity in static fusimotor neurones were not found in spinal preparations. The observations support the hypothesis of an independent control of the static and dynamic properties of primary endings of the muscle spindle. It is suggested that the activity in the dynamic fusimotor system largely is supported by dorsal root inflow, whereas the static fusimotor system mainly depends upon descending suprasegmental activation.

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