Structure and function of the tactile hair receptors on the cat's foreleg.

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AbstractThe cat's carpal sinus hairs are shown to be supplied by free nerve endings and Merkel cellneurite complexes. Using a mechanical stimulator permitting hair displacements at varying rates and amplitudes, dynamic and static responses were analyzed. Most units respond to static displacement by slowly adapting discharges which after an initial decline in frequency attain a steady state whose frequency is related to the displacement amplitude by a power function. The frequency in the dynamic phase rises with the rate of rise, increasing during the movement and decreasing as the final plateau is attained. The dynamic response is related to the rate of rise by a power function. Most of these slowly adapting receptors respond most effectively to proximal hair movements. Movement of one hair elicits responses in several units which may have reciprocal directional sensitivity. Each fiber supplies only one hair. Effects of pilomotor muscle activation on the afferent inflow were demonstrated in experiments concerning the possible existence of an efferent regulating mechanism. Above a minimum velocity some receptors discharged in the dynamic phase, being silent in the static phase. These rapidly adapting receptors responded to movements in all directions and displayed off responses. Fiber conduction velocities were determined.