Abstract
Warmth and cold sensations are known to derive from separate warm and cold cutaneous thermoreceptors in the form of differentiated afferent nerves. The firing rate of warm-sensing nerves increases as the temperature increases; the firing rate of cold-sensing nerves increases if the temperature is reduced. I postulate that the primary sensitivity of the warm sensors derives from voltage-gated Ca(2+) membrane channels configured such that an increase in temperature opens channels and increases the ion influx while a reduction in temperature increases the ion influx through voltage-gated Na(+) channels in the cold sensory nerve ends. In either case, the initial cation influx causes a small cellular depolarization that further opens Ca(2+) channels, admitting more cations in a positive feedback process that leads to the depolarization of the membrane, thus initiating an action potential pulse. Monte Carlo calculations based on a well defined model of such processes, which include effects of noise, demonstrate quantitative agreement of the model with an extensive body of data.