The Journal of Neurophysiology Vol. 78 No. 5 November 1997, pp. 2641-2648
Copyright ©1997 The American Physiological Society

Innervation Territories of Mechanically Activated C Nociceptor Units in Human Skin

Roland Schmidt¹, Martin Schmelz², Matthias Ringkamp², Hermann O. Handwerker², and H. Erik Torebjörk¹

¹ Department of Clinical Neurophysiology, University Hospital, S-75185 Uppsala, Sweden; and ² Department of Physiology and Experimental Pathophysiology, University of Erlangen, Nürnberg, Germany

Schmidt, Roland, Martin Schmelz, Matthias Ringkamp, Hermann O. Handwerker, and H. Erik Torebjörk. Innervation territories of mechanically activated C nociceptor units in human skin. J. Neurophysiol. 78: 2641-2648, 1997. Innervation territories of single mechanically activated C nociceptors in the skin of the leg and foot were explored in normal human subjects. Microneurographic recordings were obtained in the peroneal nerve from 70 mechano-heat responsive (CMH) and 7 mechano-(but not heat) responsive (CM) units. Units were identified by their constant long-latency response to intracutaneous electrical stimulation of their terminals. Responsiveness to mechanical, heat, or transcutaneous electrical stimuli was verified by transient slowing of conduction velocity after activation by such stimuli. We determined their thresholds to mechanical stimuli (mean 33.7 mN, median 30 mN, range 3-750 mN) and heat (mean 42.5°C, median 42.5°C, range 37-49°C). Most mechano-receptive fields (mRFs) were found on the foot dorsum (60 units) and some on the lower leg (14 units) and toes (3 units). Most units had one continuous mRF, but 10 units had more complex fields. Areas of mRFs mapped with a von Frey filament (750 mN) ranged from 10 to 363 mm² (mean, 106 mm²). The mRFs were oval or irregularly shaped with greatest diameters ranging from 3 to 45 mm. Mean areas of mRFs were largest on the lower leg (198 mm²), smaller on the foot dorsum (88 mm²), and smallest on the toes (35 mm²). Forty-nine of the 77 units had identical mRFs and electro-receptive fields (eRFs). Twenty-six units had larger eRFs than mRFs, whereas the opposite was found for two units only. Areas of eRFs ranged from 16 to 511 mm² (mean 121 mm²). An estimate of the innervation density based on the present data and the presumed number of C fibers in cutaneous fascicles of the peroneal nerve suggests a considerable overlap of nociceptive endings in the skin. Such overlapping nociceptor innervation in the skin allows for substantial spatial summation in response to punctate noxious stimuli, which may be a prerequisite for high accuracy in localizing painful events from a C-fiber input. The reduction in size of innervation territories distally allows for finer discrimination of spatial dimensions of noxious stimuli distally as compared with proximal regions of the extremities. Mean maximal diameters of the mechano-receptive fields of CMH and CM units on the lower leg (22.3 mm) and foot (15.3 mm) are of similar size as the radius of axon reflex flares evoked by noxious mechanical stimuli in these regions.

This article has been cited by other articles:

				L. M. Johanek, R. A. Meyer, T. Hartke, J. G. Hobelmann, D. N. Maine, R. H. LaMotte, and M. Ringkamp Psychophysical and Physiological Evidence for Parallel Afferent Pathways Mediating the Sensation of Itch J. Neurosci., July 11, 2007; 27(28): 7490 - 7497. [Abstract] [Full Text] [PDF]

				H. Bostock, M. Campero, J. Serra, and J. L. Ochoa Temperature-dependent double spikes in C-nociceptors of neuropathic pain patients Brain, September 1, 2005; 128(9): 2154 - 2163. [Abstract] [Full Text] [PDF]

				H. H. Kramer, M. Schmelz, F. Birklein, and A. Bickel Electrically Stimulated Axon Reflexes Are Diminished in Diabetic Small Fiber Neuropathies Diabetes, March 1, 2004; 53(3): 769 - 774. [Abstract] [Full Text] [PDF]

				M. Schmelz, R. Schmidt, C. Weidner, M. Hilliges, H. E. Torebjork, and H. O. Handwerker Chemical Response Pattern of Different Classes of C-Nociceptors to Pruritogens and Algogens J Neurophysiol, May 1, 2003; 89(5): 2441 - 2448. [Abstract] [Full Text] [PDF]

				J. Wessberg, H. Olausson, K. W. Fernstrom, and A. B. Vallbo Receptive Field Properties of Unmyelinated Tactile Afferents in the Human Skin J Neurophysiol, March 1, 2003; 89(3): 1567 - 1575. [Abstract] [Full Text] [PDF]

				R. Schmidt, M. Schmelz, C. Weidner, H. O. Handwerker, and H. E. Torebjork Innervation Territories of Mechano-Insensitive C Nociceptors in Human Skin J Neurophysiol, October 1, 2002; 88(4): 1859 - 1866. [Abstract] [Full Text] [PDF]

				P. S. Khalsa, C. Zhang, and Y.-X. Qin Encoding of Location and Intensity of Noxious Indentation Into Rat Skin by Spatial Populations of Cutaneous Mechano-Nociceptors J Neurophysiol, May 1, 2000; 83(5): 3049 - 3061. [Abstract] [Full Text] [PDF]

				M. Schmelz, R. Schmid, H. O. Handwerker, and H. E. Torebjork Encoding of burning pain from capsaicin-treated human skin in two categories of unmyelinated nerve fibres Brain, March 1, 2000; 123(3): 560 - 571. [Abstract] [Full Text] [PDF]

				Y. B. Peng, M. Ringkamp, J. N. Campbell, and R. A. Meyer Electrophysiological Assessment of the Cutaneous Arborization of Adelta -Fiber Nociceptors J Neurophysiol, September 1, 1999; 82(3): 1164 - 1177. [Abstract] [Full Text] [PDF]

				A. B. Vallbo, H. Olausson, and J. Wessberg Unmyelinated Afferents Constitute a Second System Coding Tactile Stimuli of the Human Hairy Skin J Neurophysiol, June 1, 1999; 81(6): 2753 - 2763. [Abstract] [Full Text] [PDF]

				M. Schmelz, R. Schmidt, A. Bickel, H. E. Torebjork, and H. O. Handwerker Innervation Territories of Single Sympathetic C Fibers in Human Skin J Neurophysiol, April 1, 1998; 79(4): 1653 - 1660. [Abstract] [Full Text] [PDF]