CBSE Class 10 Answered

Receptors for warmth and cold are specialized free nerve endings. A thermoreceptor is a sensory receptor, or more accurately the receptive portion of a sensory neuron, that codes absolute and relative changes in temperature, primarily within the innocuous range. In the mammalian peripheral nervous system warmth receptors are thought to be unmyelinated C-fibres (low conduction velocity; reaches brain within a few seconds ), while those responding to cold have both C-fibers and thinly myelinated A delta fibers (faster conduction velocity; reaches brain within one second).

A rise in skin temperature above body temperature causes a sensation of warmth, while a fall in skin temperature below body temperature is experienced as cold sensation; pain is felt if skin temperature increases above 45 °C or decreases below 10 °C; the mucous membrane of the mouth is less sensitive than the skin.

The adequate stimulus for a warm receptor is warming, which results in an increase in their action potential discharge rate. Cooling results in a decrease in warm receptor discharge rate. For cold receptors their firing rate increases during cooling and decreases during warming. Some cold receptors also respond with a brief action potential discharge to high temperatures, i.e. typically above 45°C, and this is known as a paradoxical response to heat.

The hypothalamus is involved in thermoregulation.

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