Low‐threshold mechanoreceptive and nociceptive units with unmyelinated (C) fibres in the human supraorbital nerve.

Abstract

SUMMARY1. In recordings from the human supraorbital nerve with tungsten microelectrodes, eleven afferent units with unmyelinated (C) axons were identified on the basis of their conduction velocities (0-6-1-4 m/s).2. Eight units had low mechanical thresholds (< 0-23 g) and could be activated up to their maximal firing rates of about 100 impulses/s by weak tactile stimuli, whereas three units had higher thresholds (5 5 g) and responded vigorously to noxious stimuli only.3. During a skin indentation the low-threshold units adapted to an irregular lowfrequency discharge, and release of the stimulus elicited a prominent off-response often ending with an after-discharge. Slow stroking was a particularly effective stimulus, even when done with cotton wool, whereas rapid stroking reduced the response. All types of stroking stimuli were occasionally followed by after-discharges. Repeated mechanical stimulation at short intervals resulted in a decline of the response, indicating receptor fatigue. For two units a response to skin cooling was observed.4. The above low-threshold C units have all the main characteristics of the C mechanoreceptors known from the cat and primates but not previously proven to exist in man. The high-threshold C units are similar to the polymodal nociceptors found in other human skin areas.

Activity‐dependent slowing of conduction differentiates functional subtypes of C fibres innervating human skin

“…This raises the possibility that our type 3 units could correspond to low-threshold mechanoreceptors. Nordin (1990) has described low-threshold C mechanoreceptor units in human supraorbital nerve, which discharged at up to Activity-dependent slowing in human C fibres J. Physiol. 515.3 809 Figure 13.…”

Respiratory and cardiac modulation of single sympathetic vasoconstrictor and sudomotor neurones to human skin

“…Therefore it is difficult to exclude the possibility that the maximum number of spikes and the highest instantaneous firing frequencies exhibited by a unit may be overestimated. On the other hand we could not exclude very short intervals unless the spikes differed in amplitude and shape, and it is known that non-myelinated afferents in human subjects can sustain high frequency discharges of approximately 100 Hz (Nordin, 1990;Vallbo et al 1993). The reason for the irregular firing pattern and widely varying instantaneous firing frequencies may be that a single postganglionic neurone is driven by two (or more) preganglionic neurones possessing strong synapses (McLachlan et al 1997).…”

Machine Learning for Functional Brain Mapping

“…), and a parallel network of thin, unmyelinated so called C-tactile fibers, which are primarily activated by gentle types of touch and signal hedonic, pleasant features of the tactile sensation Löken et al (2009);Olausson et al (2002); Vallbo et al (1999;. The C-tactile system was recently discovered in humans, and is currently under intense research Edin (2001); Löken et al (2007); Nordin (1990);Vallbo et al (1999). The C-tactile system is difficult to study in relation to brain processing, mainly since it cannot be activated selectively -any mechanical stimulation of the skin invariably co-activates thick, myelinated fibers in healthy subjects.…”

“…www.intechopen.com Stimulation: Light stimulation, known to vigorously activate C-tactile afferents in humans as well as in other species Bessou et al (1971); Douglas & Ritchie (1957);Edin (2001); Kumazawa & Perl (1977); Nordin (1990);Vallbo et al (1999;Zotterman (1939), was delivered using a seven centimeter wide soft brush with an indentation force 0.8 N. The experimenter manually stroked the brush in a proximal to distal direction on the right forearm or thigh. Scanning protocol: The experimenter applied the tactile stimulation according to timing cues from the scanner, and all subjects were instructed to focus on the stimulus throughout the fMRI scanning session.…”