Recovery curves of thresholds of muscle spindle, leaf-like and tendon receptors in the frog sartorius muscle after an antidromic discharge.

In three previous papers5,6,7),functional properties of spindle,leaf-like and tendon receptors in the frog sartorius muscle have been compared with each other during contractions or passive stretch of the muscle.It has been demonstrated that those properties were not only dependent upon the excitability of their sensory nerve endings,but also largely upon the visco-elastic properties of the underlying tissues where they are embedded.The present study was undertaken to clarify the excitability of the sensory nerve fibers in conditions that eliminated as possible the effects of the visco-elastic properties of their underlying tissues. Electrical stimulation of the nerve endings(LIPPOLD, NICHOLLS and REDFEARN11))seems to be best for the study,but full isolation from surrounding tissues is difficult,especially in the case of the tendon receptors which could not be isolated from the tendon tissues.Pressure stimulation of the receptors was used in the present study;as it is able to directly excite the receptors with relatively little participation of the visco-elastic properties of their underlying tissues,as has been demonstrated by BRIDGEMAN and ELDRED1).