Time constants of the slow velocity responses of deefferented primary muscle spindle endings

Responses to ramp muscle stretches of constant amplitude (10 mm) and varying velocity (0.4-70 mm/sec) were recorded from deefferented primary spindle endings in the extensor digitorum longus (EDL) and tibialis anterior (TA) muscles of the cat. A linear model was applied to the relationship between peak frequency at ramp offset and velocity and estimates of the time constants of the slow velocity responses were made by fitting theoretical curves to the experimental data. A satisfactory fit was obtained with two time constants, one always taken as 90 sec, the other ranging from 1.0 to 2.3 sec for TA and from 2.5 to 4.0 sec for EDL.