Activity-dependent variations in threshold and conduction velocity of human sensory fibers.
Activity-dependent changes in threshold with a sequential set of events (action potential, refractoriness, supernormal and subnormal period) can regularly be observed in sensory fibers of the human median nerve, the whole recovery cycle lasting for 120-200 ms in different subjects. Supernormality is probably due to an after-depolarization of the membrane potential and has its peak 5-8 ms after the conditioning pulse. The subsequent period of subnormal excitability results from a long-lasting hyperpolarization of the membrane and reaches its maximum 40-60 ms after the conditioning pulse. In contrast to some findings in slow-conducting fibers of different experimental animals, the fast-conducting fibers of the human median nerve do not reveal the phenomenon of supernormal conduction velocity.
D000200:Action Potentials; D000293:Adolescent; D000328:Adult; D004558:Electric Stimulation; D006801:Humans; D007700:Kinetics; D008475:Median Nerve / Q000502:physiology*; D008875:Middle Aged; D009475:Neurons, Afferent / Q000502:physiology*; D012016:Reference Values; D012684:Sensory Thresholds