Muscle spindle receptors and their impact on Parkinson´s disease and Cerebral Palsy subjects.

In some neurological conditions, like Parkinson's disease (PD) and Cerebral Palsy (CP), as well as with ageing, muscle spindles have been mentioned as participating in the pathological response of observed muscles. The aim of this review has therefore been to examine what is known about muscle spindle receptors, their function and how they are involved in regulating precise muscle movement in relation to these two conditions. Data from acoustic myography (AMG) studies with healthy controls (HC), CP and PD subjects have been re-examined with a view to identifying possible effects of changes in muscle movement which could be related to muscle spindle receptor function. Studies of muscle spindles have shown that during shortening and lengthening contractions the fusimotor system is activated differently with different discharge frequencies and sensitivities. With increasing age comes a loss of precise proprioception, something that coincides with a change in the AMG E-score towards lower values, indicating a reduced level of coordination and efficiency of muscle use. With PD and CP there is likewise a documented decrease in proprioception, also showing lower E-values than age-matched HC subjects. We conclude that the decrease in proprioception observed in these subjects must be partly due to a change in the muscle spindle / C-centre feedback system.