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. 2021 Jun 21;144(5):1312–1335. doi: 10.1093/brain/awab048

Table 3.

Characterization of human C-fibre nociceptors using microneurography

Nociceptor afferents and subpopulations Response characteristics Neurophysiological properties Receptive fields
C-mechanosensitive (‘polymodal’)

  • Mean mechanical response ∼30 mN (range 3.4–750 mN). Majority respond in 10–300 mN range

  • Weak and transient response to algogensa

  • Respond to cowhage and histamine

  • ADS: Low latency changes during low-frequency stimulation e.g. <2% during 5 min 0.25-Hz stimulation

  • High (>10%) latency changes during 2-Hz stimulation

  • CV ∼1 m/s

  • 10 mA activation thresholdb

  • 100 mm2 (10–363 mm2)

  • Uniform shape, some irregular; size varies depending on body site
C-mechano-heat Mean temperature response ∼40°C; >45°C linear response between stimulus temperature and firing frequency
C-mechano-heat-cold Also respond to cold <20°C
C-high threshold mechanoreceptors Only respond to mechanical stimuli; no thermal response
C-mechanoinsensitive

  • Unresponsive or very strong mechanical stimulus >750 mN

  • Thermal response at >48°C

  • Strong and sustained response to algogens (unresponsive to endothelin 1)

  • ADS: High latency changes during low-frequency stimulation e.g. >5% during 0.25-Hz stimulation

  • High (>10%) latency changes during 2-Hz stimulation

  • CV ∼ 0.8 m/s

  • >30 mA activation thresholdb

 500 mm2, discontinuous patches, irregular in shape, heterogeneous physiological response properties across receptive field
C-mechanoinsensitive-heat- insensitive (‘silent’) Unresponsive to mechanical/thermal stimulus; can be sensitized after algogen (mustard oil/capsaicin) application
C-mechanoinsensitive-histamine-positive (‘pruriceptors’, C-itch afferents) Very sensitive to histamine, no response to cowhage

From human in vivo microneurography studies C-fibre nociceptive afferents comprise two classes. This table summarizes key differences between C-mechanosensitive nociceptors and C-mechanoinsensitive afferent responses to mechanical, thermal, and chemical stimuli. C-mechanosensitive nociceptive afferents are also called type 1A fibres and C-mechanoinsensitive type 1B fibres. ADS = activity-dependent slowing; CV = conduction velocity.

a

Algogens include mustard oil, capsaicin, bradykinin, acetylcholine, serotonin, prostaglandin E2, and endothelin 1.

b

In response to monopolar skin surface stimulation.