This term is used here to denote the reduction in preparedness for action found in the muscles when there are defects in certain areas of the extra-pyramidal part of the central nervous system . In this case the excitatory influence exerted by the extra-pyramidal system upon the motoneuron pools is diminished and as a result, the muscles show a reduction in sensitivity to stretch. This may, at first sight, be confused with muscle paralysis because the muscles may appear to be totally or almost totally flail. It is, however, very different.
The muscles have a normal lower motor neuron supply but the factors exerting an influence upon the motoneuron pools are seriously disturbed. There is a reduction of excitatory influence upon the small anterior horn cells which give rise to the fusimotor fibres. Because of this the fusimotor fibres are inactive and therefore activity of the intrafusal…
