Thermal sensation: warm and cold receptors
- Mechanism
- For completeness
Separate nerve endings in the skin report cold and warmth; extreme cold or heat switches on pain endings instead.
Also called: Thermoreceptors, TRP channels
See it in 3D: Skin · Dorsal root ganglia · Spinal cord · Thalamus
What it is
Skin temperature is sensed by three groups of free nerve endings: cold receptors, warm receptors and thermal pain receptors. Each group fires most over its own temperature range, and the brain reads the temperature from the mix of their activity. Temperature-gated TRP ion channels are the transducers. The signals ascend with pain in the anterolateral system.
How it works, step by step
- Temperature changes the gating of TRP channels in the free nerve endings, letting cations in and depolarizing the ending.
- Below ≈ 15 °C cold-pain fibres start firing; cold fibres peak near ≈ 25 °C and fade above ≈ 40 °C.
- Warm fibres start ≈ 30 °C and peak ≈ 40–45 °C; above ≈ 45 °C heat-pain fibres take over.
- Near ≈ 30–36 °C both cold and warm fibres fire little, and skin feels neutral.
- Above ≈ 45 °C some cold fibres fire again, so very hot water can briefly feel cold (paradoxical cold).
- Large areas sum their input: warming the whole body is noticed at much smaller changes than warming a fingertip.
Approximate skin temperature ranges (illustrative)
| Parameter | Value |
|---|---|
| Cold pain | below ≈ 10–15 °C |
| Cold fibre peak firing | ≈ 25 °C |
| Thermally neutral skin | ≈ 30–36 °C |
| Warm fibre peak firing | ≈ 40–45 °C |
| Heat pain (TRPV1) | above ≈ 43–45 °C |
Approximate values for a healthy adult at rest; each laboratory sets its own ranges.
Clinical notes
- Syringomyelia: a cyst in the central cord cuts crossing fibres in the anterior white commissure, giving 'cape' loss of pain and temperature with touch preserved.
- Small-fibre neuropathy (e.g., diabetes) often removes temperature sense first, so burns go unnoticed.
- Lateral medullary infarct: loss of pain and temperature on the ipsilateral face and contralateral body.
Test yourself
Think of the answer, then tap the question to see it.
Why does a menthol lozenge feel cold although it does not lower temperature?
Menthol opens TRPM8, the same channel that cooling opens in cold receptor endings, so the brain reads the signal as cold.
A patient with a cervical syrinx burns both hands without noticing but feels light touch normally. Why?
The syrinx cuts pain and temperature fibres crossing in the anterior white commissure; touch travels in the dorsal columns, which are spared early.
Why do you feel the cold of a metal handle faster than the warmth of a heater?
Cold signals travel partly on myelinated Aδ fibres, while warmth travels on slower unmyelinated C fibres.
Why does a warm bath feel less warm after a few minutes?
Thermoreceptors respond strongly to change and then partly adapt, so firing falls while the skin temperature stays the same.
Connections
See it in 3D4
The structures of Durgical's 3D anatomy where it happens.
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: Physiology, Integument (StatPearls (NCBI Bookshelf), 2024); Neuroanatomy, Spinal Cord (StatPearls (NCBI Bookshelf), 2024); Neuroanatomy, Medulla Oblongata (StatPearls (NCBI Bookshelf), 2024).
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Representative model, for educational purposes only.