Fusimotor »Set« vs. α-γ Linkage in Voluntary Movement in Cats
The performance of voluntary movement can be influenced by spindle afferent activity at a number of different levels of the central nervous system. Spindle afferents themselves are in turn strongly influenced by the CNS, via activity in fusimotor efferent fibres. Two categories of fusimotor neurones, static and dynamic, are commonly distinguished. In experiments on reduced preparations the functional properties of these fusimotor fibres have been investigated in great detail. At present it seems permissible to state that static and dynamic fusimotor neurones are equipped with the requisite properties to act, together, as a gain or sensitivity-controlling system. However, what is rather poorly understood, is how, and to what end, fusimotor neurones are in fact used during natural movements. Owing to the fact that direct recordings from identified fusimotor neurones under these conditions have not so far been achieved, present knowledge of fusimotor function is restricted to qualitative and often uncertain deductions from spindle afferent recordings during natural movement.
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