Characteristic curves of the dynamic response of primary muscle spindle endings with and without gamma stimulation.

Abstract

1. The characteristic curves of the dynamic response of primary muscle spindle endings (i.e. the dependence of dynamic response on the stretch volocity) have been recorded with and without gamma stimulation in 75 muscle spindles of the cats' M. tibialis anterior. They can be described by a power function DR=a · vr.n 2. Under dynamic fusimotor stimulation the prefactor ‘a’ increases and the exponent ‘n’ decreases; under static gamma stimulation vice versa. 3. The characteristic curves with and without gamma stimulations of a single spindle are intersecting, because of the change of the exponent ‘n’. 4. The dyamic response under dynamic gamma stimulation usually increases, but we observed a decrease, too. Under static gamma stimulation the dynamic response usually decreases. 5. In the following we looked on the gamma stimulations statistically. We had 47 dynamic gamma stimulations. Here we observed a separation into an upper and a lower group of the characteristic curves, which proved to be statistically significant, according to their effects on the course of the characteristic curves and the velocity sensitivity. 6. The lower group of the dynamic gamma stimulations and all 24 static gamma stimulations do not differ significantly i) from the group of characteristic curves without gamma stimulation and ii) in the absolute course of the characteristic curves and in the velocity sensitivity under gamma stimulation. 7. The upper group of dynamic gamma stimulations is the only one to cause significantly strong effects on the course of the characteristic curves and velocity sensitivity. 8. The upper group of dynamic gamma fibre stimulations extends the measurable velocity range to very small stretch velocities, which otherwise do not cause a measurable dynamic response.