Nonpainful temperature sensations originate from receptors in the skin and they depend on the
neocortex for their conscious appreciation.
Thermoreceptors are neurons that are exquisitely sensitive to temperature. Temperature-
sensitive neurons clustered in the hypothalamus and the spinal cord are important in
maintaining stable body temperature. Thermoreceptors in the skin contribute to our perception
Temperature sensitivity is not spread uniformly across the skin. Some spots about 1 mm wide
are especially sensitive to either hot or cold, but not both. The fact that the locations of hot and
cold sensitivity are different demonstrates that separate receptors encode them.
The sensitivity of a sensory neuron to a change in temperature depends on the type of ion
channels the neuron expresses. Receptors responding to temperatures above 43°C are ‘hot’
receptor proteins called Trpv1. ‘Cold’ receptor are Trpm8 and are activated by nonpainful
decreases in temperature below 25°C.
There are six distinct Trp channels in thermoreceptors that confer different temperature
sensitivities (see Fig. 12.34). Different thermoreceptive neurons appear to express only a single
type of channel. This explains how different regions of skin can show distinctly different
sensitivities to temperature.
An exception is the cold receptors that also exp