Signal
How the body detects and transmits temperature.
Temperature is detected at the skin.
The skin contains specialized sensory neurons called thermoreceptors. When skin temperature changes, these receptors generate electrical signals that travel via afferent nerve fibers to the spinal cord and brain. This is how the nervous system becomes aware of temperature changes in the external environment.
Cutaneous thermoreception is established physiology. Cold-sensitive neurons primarily express the TRPM8 ion channel, which activates at skin temperatures below approximately 28 °C and increases firing rate as temperature decreases. Source records pending — evidence ledger in progress.
Skin temperature is not core temperature.
The temperature your skin registers during cold exposure is not the same as your body's core temperature. Localized cold application changes skin temperature rapidly, but core temperature changes slowly and requires sustained, extensive cooling.
The signal is not the interpretation.
When TRPM8 channels activate, they send a signal. That signal arrives in the brain. But what happens next — the feeling of discomfort, the urge to remove the cold, the interpretation of whether the sensation is tolerable — involves processing well beyond thermoreception.
The next chapter, Notice, examines how people perceive and interpret these internal body signals. The signal itself is physiology. Its interpretation is where individual experience begins.