DEPOLARIZATION OF THE CENTRAL TERMINALS OF CUTANEOUS AFFERENT FIBERS

Abstract

The depolarizing action of cutaneous and muscle afferent volleys on the central terminals of cutaneous fibers has been studied directly by intracellular recording, and also indirectly by testing for increases in excitability as measured by responses to applied current pulses. Group Ia afferent volleys from muscle had no action, but all other medullated afferents from muscle, Groups Ib, II and III, regularly had a depolarizing action, particularly when applied by brief high frequency bursts, though it was usually smaller than the depolarization produced by single cutaneous volleys. The dorsal root potentials produced by prolonged tetanization of cutaneous nerves, declined from an initial peak to a plateau which may be as large as 80% of the peak height, and which continued at a steady level for several seconds. These prolonged depolarizations give a continued presynaptic inhibition and hence are a very effective negative feed-back device that operates upon all flexor reflex afferents.