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 express Trpv1. They are also sensitive to
temperature increases above 43°C. If heat is restricted to small regions of skin
innervated by a cold receptor, it can produce a paradoxical feeling of cold.
Thus, the CNS does not know WHAT kind of stimulus causes the receptor to fire, but it
continues to interpret all activity from its cold receptor as a response to cold.
Responses of thermoreceptors adapt during long-duration stimuli (see Fig. 12.35). The
differences between the response rates of warm and cold receptors are greatest during, and
shortly after, temperature changes. Our perceptions of temperature often reflect these skin
It is the sudden change in the quality of a stimulus that generates the most intense
neural and perceptual responses
The Temperature Pathway
The temperature pathway is virtually identical to that of the pain pathway.
Cold receptors are coupled to Aδ and C fibers while warm receptors are coupled to only
Small-diameter axons synapse within the substantia gelatinosa of the dorsal horn.
The axons of second-order neurons immediately decussate and ascend in the
contralateral spinothalamic tract.
o If the spinal cord is transacted on one side, there will be a loss of temperature
sensitivity on the opposite side of the body.