Observations on reflex responses to rhythmical stimulation in the frog

Abstract

The primary object of this investigation was the study of the relation between the frequency and intensity of stimulation, and the resulting reflex reactions. I first studied the effect of alteration of frequency at a given intensity of stimulation and found that under these conditions the frequency has an optimal value. With moderate and rapid frequency stimuli there is also an optimal intensity value, though with those of low frequency this is not the case. It was also hoped that some light might be thrown on the mechanism of the spinal reflex centre by the comparison of the isometrically recorded reflex tetanus, with the tetanus obtained directly by stimulation of the efferent nerve at varying intensity and frequency of stimulation. In particular, an attempt was made to settle the question as to whether stimulation of a nerve can set into action the whole of the reflex centre to which it is afferent. Camis (4) concluded that the cells of a spinal motor centre can be regarded from a functional point of view, as divided into several independent groups, though this division is not absolute. On the other hand, Dreyer and Sherrington’s (5) observations point rather to the physiological unity of the spinal motor centre; since they showed that the maximal mechanical power of tetanic contraction, obtainable from a muscle under spinal reflex action, is sometimes as great as that which can be evoked from it by direct faradisation of the motor nerve itself.