Thermoreceptors

The Skin thermoreceptors are the naked terminals of small diameter afferents. They are slowly adapting and tonically active. The Thermoreceptor afferents each have merely 3-4 terminals and have very small RFs, however infrared radiation is poorly localized.

There are two kinds of thermoreceptor, warm and cold, that fire over various temperature ranges as shown in figure below. They do not react to noxious temperatures. The Skin temperature is perceived by comparing the associative activities of the warm and cold receptors. Thermoreceptors signal the direction in which the temperature modifies. The Skin cooling temporarily silences warm receptors and causes the cold receptor firing rates to increase. Likewise, skin warming silences the cold receptors and boosts the warm receptor firing.

                         Figure: The Frequency response of populations of cutaneous cold & warm thermoreceptors.