New specific sensory structures in hairy skin

Abstract

1. Cutaneous “touch spots” in hairy skin, with mechanical thresholds as low as 2 mg. weight, were identified by recording electrically from single myelinated cutaneous afferent nerve fibres in anaesthetised cats. 2. The discharge elicited by mechanical stimulation of a “touch spot” was slowly-adapting. Movements of the adjacent hairs were ineffective stimuli unless the hairs were pressed down on to the “touch spot”. A brief low frequency afferent discharge could be elicited by lowering the temperature of the skin. 3. The “touch spots” could be seen on the surface of the skin in the living animal as hemispherical domes, 100 to 250 μ diameter. Histological examination of a “spot” showed a specialised epithelium, containing flat terminal nerve discs, 10 μ diameter, innervated by branches of a single thick myelinated axon. 4. It is suggested that the results provide strong support for the concept of a specialisation of function and structure in some cutaneous afferent nerves.