Abstract
In large mixed nerves, such as the sciatic, the action potential started by local stimulation is much more protracted after conduction than at the locus of stimulation, and, in the former case, presents 3 principal elevations of the continuous potential. 1 Bishop and Heinbecker recognize 4 main elevations and believe that the potentials contributed to these elevations are supplied by fibers of different types.2, 3 Measurements of the duration of axon potentials hitherto have been based on superimposed axon responses recorded at the site stimulated. Inasmuch as axons respond to stimulation with different latencies 4 this method cannot give the axon potential in its true form. By employing nerves containing only a few fibers at the lead, long distances of conduction and very high amplification, it is possible to record discretely the undistorted potentials of some, often of all, and to ascertain the characteristics of each, of the constituent axons.
When either the relative voltage of threshold induction shocks or the rheobasic voltage from a condenser is plotted against conduction rate the resulting curves both are hyperbolic in form, the slower fibers having the higher thresholds. Likewise a smooth curve, hyperbolic in form, can be drawn between the points relating time to maximum of the action potential to conduction rate; the slower the conduction rate the longer is the time to maximum. And in so far as it is possible to correlate the data on the relation of the absolutely refractory periods to conduction rates the result is a similar hyperbolic curve. The refractory periods without exception are longer than the corresponding times to maximum. The data on action voltage, due to possible occasional failure to recognize deflections produced by 2 perfectly superimposed axon potentials, are not absolutely reliable.
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