Thermoreceptors & Mechanoreceptors: Sensory Physiology of Temperature & Touch
Specialized cutaneous nerve endings transduce physical stimuli into neural signals:
| Receptor Type | Stimulus | Primary Subtypes | Fiber Type | Key Features |
|---|---|---|---|---|
| Thermoreceptors | Temperature change | Cold (TRPM8), Warm (TRPV3/4), Noxious cold/heat (TRPA1, TRPV1) | Aδ (cold), C (warm/pain) | Phasic-tonic adaptation; encode ΔT, not absolute T |
| Mechanoreceptors | Mechanical deformation | Merkel (SA1), Meissner (RA1), Ruffini (SA2), Pacinian (RA2) | Aβ (all) | Differ in adaptation, receptive field, frequency tuning |
Clinical Relevance
- Peripheral neuropathy: Small-fiber loss → impaired temperature/pain (thermoreceptors/nociceptors); large-fiber loss → vibration/proprioception loss (mechanoreceptors).
- Diabetic neuropathy: Often small-fiber first → burning feet, thermal insensitivity.
- Herpes zoster: Viral damage to dorsal root ganglion → allodynia, thermal hyperalgesia.
- Spinothalamic tract lesion: Contralateral loss of pain/temperature; dorsal column lesion → ipsilateral vibration/position loss.
Testing
- Bedside: Tuning fork (vibration), cotton swab/wisp (light touch), cold/warm test tubes (temperature), pinprick (pain).
- Quantitative: QST (quantitative sensory testing), skin biopsy (intraepidermal nerve fiber density).
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