The Influence of Muscle Pain on Spinal Reflexes. *

Abstract

Summary

Stimuli such as injection of hypertonic NaCl solution into striated muscle or faradization of muscles which cause “muscle pain” in man, and pupillary dilatation and vocalization in the anesthetized animal modify spinal reflexes in the latter. It is shown that in general ipsilateral “painful” stimuli increase the response of a flexor reflex and diminish the response of the knee jerk to a standard stimulus. On the other hand, contralateral “pain” stimulation causes an increase in the knee jerk and a decrease in the flexor reflex. If excessive stimuli are used the knee jerk may be inhibited not only from the ipsi- but also from the contralateral side. The fact that “muscle pain” greatly enhances the effect of electrical stimulation of the motor cortex is not due to the alteration of spinal centers but suggests the involvement of supraspinal mechanisms.