Recruitment type of reflexes

Abstract

In our previous papers comparison between isometric myograms of the ipsilateral knee flexor reflex and of the crossed knee-extensor reflex was, for the latter, practically confined to the decerebrate condition. We here supplement it by observations on the crossed knee-extensor reflex in the purely spinal preparation. The observations have been made after spinal transection in the 1st lumbar segment at times varying between two and nine days subsequent to the transection. The severance of the cord has been performed under deep anæsthesia and with full precautions for asepsis. At the subsequent examination of the reflexes the animal (cat) was decerebrated under profound anæsthesia. The myograph was, as before, isometric. The characteristics attaching to the crossed extensor’s reflex, as described in our previous papers, we find largely obtain in the spinal preparation also. The ascent curve of the reflex has the long climbing course (fig. 1, A, B, C). Its duration has, in these experiments, varied between 1·3 seconds and 9 seconds, and in the latter instance the stimulus was finally withdrawn while the ascent was still in progress. In one experiment (4th day subsequent to spinal transection) the form of the ascent resembled somewhat that shown in fig. 12 E of the previous paper, there taken from a decerebrate preparation. In other experiments the ascent began less steeply and was of longer continuance, resembling the sub-variety D of fig. 12 of the decerebrate records. In this form the contraction tended to commence with a single small step followed by a slight decline before entering, perhaps a third of a second later, on its gradual continuous course of ascent. Besides the characteristic slow prolonged ascent the reflex in its spinal form likewise presents relative insensibility to omission of a stimulus from the series exciting the afferent nerve, a feature noted in the decerebrate condition. Thus the suppression, during the course of the reflex, of one member of a series of break-shocks at 28 per second caused no remission whatever of the tension obtaining in the myogram, resembling in so far the result instanced in fig. 9 of a previous paper illustrating the decerebrate reaction.