Analysis of the dynamic responses of deefferented primary muscle spindle endings to ramp stretch

A detailed analysis of the complex dynamic response of 8 deefferented primary muscle spindle endings to ramp stretches of the extensor digitorum longus muscle (EDL) was made in anaesthetized cats. The analysis was based on Lennerstand's linear muscle spindle model, in which the dynamic peak, i.e. the peak frequency at the end of the dynamic phase of a ramp stretch, is assumed to consist of three components: a position response, a slow velocity response, and a quick velocity response. The components of the dynamic peaks analysed were fairly well correlated with the static behaviour of the primary muscle spindle endings, the latter, in turn, being regarded as an indicator of the spindles' location in the non-homogeneous extrafusal muscle. The results thus provide a satisfactory explanation of the high correlations between the static and gross dynamic behaviour of deefferented primary muscle spindle endings of the EDL previously reported from our laboratory.