CORD CELLS RESPONDING TO TOUCH, DAMAGE, AND TEMPERATURE OF SKIN

Abstract

Primary afferent" neurons of skin and the cells on which they end in the spinal cord have been studied in spinal cats with intracellular microelectrodes. Afferent fibers: (1) Single light touch fibers innervate areas averaging 5x4 mm. (2) Pressure-sensitive A fibers form a continuous group within which the threshold varies with fiber diameter. (3) Pattern of discharge in a single fiber is fixed by the intensity and duration of the stimulus, and by the position of the stimulus within the sensitive area. (4) Some of the smaller fibers respond both to pressure and temperature. Primary Central Cells: (1) Cells that respond to light touch are arranged in a definite lamina in the dorsal part of the dorsal horn. Within this lamina there is a topographic organization, with the peripheral part of the leg medial and the proximal part lateral. This region is also shown to be the termination of the fast-conducting fibers of skin nerves. (2). Each central cell responds to light touch in a contiguous oval area of skin with an average size of 63 x 32 mm. (3) The afferent fiber projection shows no signs of a subliminal fringe. (4) The afferent fibers converging onto a single cell run together in a small microbundle in the dorsal root. (5) All cells that respond briefly to light touch also respond with a prolonged discharge to heavy pressure and to temperature. (6) It is suggested that fibers of many different diameters converge onto these cells so that they respond to all modalities of skin sensation, but differences in the pattern of discharge depend on the nature of the stimulus.