Observations on the effects on spindle primary endings of the stimulation at low frequency of dynamic beta-axons.

Stimulation of single dynamic beta-axons at presumed physiological frequencies (10-30/s) significantly increases the sensitivity of spindle primary endings of cat peroneus brevis muscle to ramp and sinusoidal stretches. This action becomes greater as the amplitude of stretch and the initial muscle length is increased. Stimulation at low frequency of two dynamic beta-axons supplying the same spindle greatly enhances the effect elicited by each axon individually.