Hair Discs and Pacinian Corpuscles Functionally Associated with the Carpal Tactile Hairs in the Cat

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Abstract
A hair disc containing Merkel cell‐neurite complexes at the base of the epidermis lateral to each carpal sinus hair in the cat is demonstrated. The physiological properties of these receptors and of the Pacinian corpuscles around the sinus hair root were analyzed using electro‐physiological techniques and a mechanical stimulator permitting displacements at different rates and amplitudes. The hair disc receptor could be excited by direct mechanical stimuli and by lateral deflection of the hair. The dynamic response was displacement‐rate sensitive. The slowly adapting static response was related to the displacement amplitude. The Pacinian corpuscles followed a sinusoidal skin stimulation from 20 c/s to 300–400 cis. A plot of the lowest amplitude giving one imp/cycle at different frequencies gave a U‐shaped curve with lowest threshold at 125–250 c/s. These receptors were also sensitive to vibratory stimulation of the hairs; on rapid hair displacement on and off responses resulted. An example is given of simultaneous activation of slowly adapting hair receptors and Pacinian corpuscles by displacement of a hair. The functional significance of the unique combination of four different types of mechanoreceptor in “the tactile hair organ” is discussed.