Functional properties of mechanoreceptors in glabrous skin of the raccoon's forepaw

Abstract

Utilizing a mechanical stimulator which permits precise control over the velocity and extent of skin displacement, response properties of 76 single myelinated median nerve fibers innervating mechanoreceptors in raccoon glabrous forepaw skin were examined. All units fell into one of two categories, rapidly adapting (34 units), responding only during skin movement, and slowly adapting (42 units), responding during both moving and static phases of skin displacement. Both types had single receptive fields, 85% of which were less than 1 mm 2 in diameter, and low thresholds to mechanical displacement. Frequency of discharge during the moving phase of stimulation was a power function of velocity for both types, but discharge patterns varied. Power function slope constants were greater for the rapidly adapting units, but the slowly adapting units exhibited a higher maximum discharge rate. Results are discussed with particular reference to the possible roles of these receptors in tactile exploratory behavior.