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Recovery of excitability of cutaneous afferents in the median and sural nerves following activity
Author(s) -
Lin Cindy S.Y.,
Mogyoros Ilona,
Burke David
Publication year - 2000
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/(sici)1097-4598(200005)23:5<763::aid-mus14>3.0.co;2-d
Subject(s) - sural nerve , refractory period , cutaneous nerve , medicine , stimulus (psychology) , median nerve , nerve conduction velocity , electrophysiology , sensory system , anatomy , forearm , neuroscience , anesthesia , psychology , psychotherapist
In acquired polyneuropathies, symptoms and signs are typically distal and symmetrical, more prominent in the lower limbs than the upper limbs. This study was undertaken to measure the extent of the decrease in excitability produced by single impulses and by impulse trains in cutaneous afferents in the median and sural nerves, and to compare the resulting changes in excitability of these afferents. Threshold tracking was used in 10 healthy subjects to measure the changes in threshold for a compound sensory action potential of 50% maximum produced by conditioning stimuli. Following a single supramaximal conditioning stimulus, the threshold changes occurring during the refractory and supernormal periods were identical for the two nerves, but there was a greater increase in threshold during the late subnormal period for median afferents. Following a train of 10 supramaximal conditioning stimuli, threshold increased by ∼40% for median afferents and by ∼20% for sural afferents. These differences are consistent with differences in a slow K + conductance. It is suggested that the hypo‐excitability produced by brief trains of impulses may be sufficient to disturb conduction in diseased nerve fibers, and that the lesser expression of slow K + conductances on cutaneous afferents in the sural nerve could render them more sensitive to depolarizing stresses than median afferents. This could be a factor in the ease with which sural afferents become ectopically active in polyneuropathies. © 2000 John Wiley & Sons, Inc. Muscle Nerve 23: 763–770, 2000