Differences in activity‐dependent hyperpolarization in human sensory and motor axons

摘要: The present study was undertaken to determine whether activity-dependent changes in axonal excitability are greater motor axons than cutaneous afferents for the same impulse load. In nine healthy subjects, supramaximal stimulation at 8 Hz delivered median nerve wrist. Changes threshold current required generate compound and sensory potentials approximately 50% of maximum other indices were tracked before after repetitive 10 min. long-lasting produced a prolonged depression both axons, with gradual recovery control levels over 15-20 These associated reduction refractoriness, an increase supernormality decrease strength-duration time constant, consistent hyperpolarization. Greater occurred axons: increased by 9.9% 16.4% test stimulus durations 0.1 1 ms, respectively, 5.4% 8.3% afferents. With higher frequencies thereby loads, could be induced It is argued that hyperpolarization resulted from activity electrogenic Na(+)-K+ pump, it requires > 125 ms restore resting state following action potential, significant intracellular Na+ accumulation occurs during steady 8-Hz train. findings imply physiological discharge rates will activate pump produce hyperpolarization, extent which vary A plausible explanation due less inward rectification as result hyperpolarization-activated cation conductance (IH)