PROPERTIES OF THE NERVE FIBERS OF SLOWEST CONDUCTION IN THE FROG

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Abstract
All of the components of the action potential that have been recognized in frog A fibers can be identified in frog C fibers. A spike lasting 8 [plus or minus] msec. is followed immediately by a large positive after-potential lasting 1 to 2 sec. Intercurrent in the trough of the latter there occurs a vestigial negative after-potential. When the nerve has been previously conditioned by a tetanus, the neg. after-pot. in a single response is large; and the pot. develops to enormous proportions in nerves poisoned with veratrine. It is then followd by a 2nd pos. pot.; the pos. after-pot. normally seen in a single action now appears as an incisure in the early part of the neg. after-pot. Tetanization increases both the neg. and the pos. after-pot. At the end of the tetanus the pos. after-pot. appears in 2 parts, of which the 1st portion corresponds to the potential following a single spike. The size and duration of the 2nd part depend upon the severity of the tetanus. The absolutely refractory period lasts 7.5 to 8.5 msec. The spike then recovers through a relatively refractory period to a supernormal height, and the supernormality lasts until the pos. after-pot. is dissipated. In a train of spikes staircasing occurs. The excitability, on the other hand, does not become supernormal. Recovery is arrested short of completion at about 30 msec, and there supervenes a subnormal period lasting as long as the pos. after-pot. In modified states in which neg. after-pots. develop, supernormal excitability appears.