The properties of 125 C fibre units recorded from the peripheral nerves of conscious man were studied. On the basis of receptive field properties and responses to natural stimulation, 120 of the units were classified as polymodal C nociceptors. Five of the units were identified as specific C warm receptors. In contrast to the polymodal nociceptors, which often had comparatively large and complex receptive fields with several receptive maxima, receptive fields of the thermo-receptors consisted of one single spot. Polymodal nociceptors responded readily to moderately intense and noxious mechanical stimuli whereas the warm receptors produced inconsistent responses to even intense mechanical skin stimulation. Thermal stimulation in the innocuous range, perceived as warmth, optimally excited the thermoreceptors whereas the polymodal C nociceptors fired most intensely to noxious painful heat.
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