The effect of low amplitude muscle vibration on the discharge of fusimotor neurones in the decerebrate cat.

Abstract

Longitudinal vibration (50-100 .mu.m, 100-300 Hz) was applied to the triceps surae tendon to examine its effect on the tonic discharges of gastrocnemius medialis fusimotor neurons in the decerebrated cat. For 19 of 27 fusimotor neurons vibration consistently caused a small rise in discharge frequency. The remaining 8 neurons showed no response to the vibration which always evoked a considerable discharge in .alpha. motoneurons. The reflex excitation of fusimotor neurons was attributed to activity in primary endings of muscle spindles, since control experiments confirmed that these receptors were powerfully excited by the vibration used, whereas secondary endings and Golgi tendon organs remained unaffected. Tonic discharges of fusimotor neurons of unknown destination were also recorded from lumbar 7 and sacral 1 ventral root filaments in decerebrated cats. Of 30 cells 7 were inhibited, 5 were excited and the remaining 18 units were unaffected by vibration of the triceps surae. These findings are discussed in relation to the role of muscle stretch receptors in the autogenetic control of fusimotor neurons.