POTENTIALS PRODUCED IN THE SPINAL CORD BY STIMULATION OF DORSAL ROOTS

Publisher Website
Google Scholar
Abstract
Electrodes were placed on the dorsum of the spinal cord of the cat in various positions with respect to one of the larger lumbar roots and the potentials induced in the cord by stimulation of the root with single induction shocks recorded with a cathode ray oscillograph. The first event recorded is a spike with the constants known to obtain in peripheral nerve. It obviously arises in the intramedullary course of the dorsal root fibers. Because the potentials do not seem to be generated in either the first or the last neurone, they have been designated as intermediary potentials and are differentiated according to their sign as positive or negative. They increase in size with the strength of stimulation; they are prolonged by cooling and are very sensitive to asphyxia but resistant to narcosis. Immediately following the spike there appear 2 much larger waves, one recording in the negative direction with a mean crest time of 2.2[sigma] and an apparent duration of 10.2[sigma], the other recording in the positive direction with a crest time of 20[sigma]- and a duration of 80 to 100[sigma]. With threshold responses or in deep anesthesia the waves are smooth; but when reflexes develop, additional potentials appear which are spike-like in character. After the production of one negative intermediary potential wave a second one of the same area cannot be produced until 70[sigma] or longer, whether the stimuli be applied to the same or adjacent roots. Simultaneous stimulation of adjacent homolateral roots results in a negative wave much smaller than the sum of the two component waves, indicating that the wave is produced at a point at which convergence has already taken place. As the potentials cannot be produced by stimulating an anterior root antidromically, they are believed to arise in internuncial neurones.

This publication has 1 reference indexed in Scilit: