Peripheral projections of nociceptive unmyelinated axons in the human peroneal nerve.
1. Previous knowledge of the anatomical course of unmyelinated (C) axons along a peripheral nerve has been scarce and has led to the concept of the axons in a constantly interchanging position. 2. Results obtained by microneurography in the peroneal nerve at knee or ankle levels in awake humans demonstrated that the receptive fields of neighbouring C units in the nerve cluster in close vicinity on the skin of the foot or the ankle. These findings indicate that C afferents run closely together throughout large portions of the peripheral nerve. 3. Intraneural microstimulation performed at neural sites where nociceptive C units were recorded induced painful sensations projected to the skin. When the stimulus intensity was increased, there was typically a concentric increase in the area of projected pain, rather than recruitment of several scattered pain projections. This finding further supports the hypothesis of a neighbouring relation of nociceptive C axons within nerve fascicles, implying spatial recruitment of adjacent axons in the nerve with adjacent peripheral projections. 4. A pain locognosia test performed during ischaemic block of impulse conduction in myelinated fibres demonstrated a fairly precise cerebral localization of noxious events on the foot from the input of C afferent fibres alone.
Jørum
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Department of Clinical Neurophysiology, University Hospital, Uppsala, Sweden.
Lundberg
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LE
Torebjörk
H E
HE
D000328:Adult; D001369:Axons / Q000502:physiology; D005260:Female; D005528:Foot / Q000294:innervation; D006801:Humans; D008297:Male; D009434:Neural Pathways; D009475:Neurons, Afferent / Q000502:physiology; D009619:Nociceptors / Q000502:physiology*; D010146:Pain; D010543:Peroneal Nerve / Q000502:physiology*; D011930:Reaction Time; D011999:Recruitment, Neurophysiological / Q000502:physiology; D012867:Skin / Q000294:innervation