29- Temperature Perception (4.6.26)

Temperature Perception

4.6.26

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• Thermoreceptors - receptors in the skin that detect temperature

• 3 main types:
• warm
• cool
• nociceptive (pain)

• Thermoreceptors - receptors in the skin that detect temperature

• 3 main types:
• warm
• cool
• nociceptive (pain)

Warm & cold fibers are responsible for the majority of temperature perception.

Warm fibers

Warm fibers are most active for skin temperatures between 75-115°F.

Cold fibers

Cold fibers are most active for skin temperatures between 50-104°F.

Warm, cold, and nociceptive (pain) fibers work together to signal skin temperature.

Extreme Heat

Warm fibers do not continue to detect heat when it gets too hot (e.g., extremely hot and harmful temperature of 45°C (113°F) or hotter

• Instead nociceptors (for pain perception) respond

Extreme Cold

Cold fibers do not respond to very cold temperatures, below 10°CAgain, nociceptors respond initially

• However, with sustained very cold temperatures, cold fibers eventually stop sending signals

Neither Hot Nor Cold

• When skin temperature is maintained at 30° to 36°C (86° to 97°F), a person does not notice a thermal sensation.

• Note that both warm and cold receptors respond at these temperatures.

• Thus, despite sensation (response of thermal receptors), the person doesn't register temperatures in this range as hot or cold.

• Exception: if temperature is abruptly changed across this range.

Abrupt Changes in Temperature

• Abrupt changes in skin temperature are signaled by changes in firing rate of temperature-sensitive fibers
• Which fiber type depends on which direction of change

• Purpose: Abrupt changes in temperature signal that some feature of the environment has changed (and may need to be responded to)

Skin abruptly warmed --> warm fiber firing rate increases

Skin abruptly cooled --> cold fiber firing rate increases

Skin temperature-induced changes in firing rate

• Warm & cool fiber firing rate has to do with which types of ion channels are open

• The more extreme the temperature, the more channel types are open

Opposing changes occur in the skin in response to warming vs. cooling

When the skin is warmed

When the skin is cooled

Responses to abrupt changes in skin temperature can be used to benefit deeper tissues (i.e. muscle, bone)

The brain can also respond to changes in blood temperature (instead of skin temperature).

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