THE ELECTRICAL EXCITABILITY OF MAMMALIAN STRIATED MUSCLE

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Abstract
The electric responses of muscles stimulated directly are readily distinguished by their promptness from the responses elicited by indirect stimulation in which the neuromuscular delay causes a lag. The electrical excitability of innervated muscles stimulated directly could thus be studied independently of that of the corresponding nerve fibers. The electrical excitability of both nerve and muscle decreased after some mins. (20 to 60) of repetitive stimulation. This decrease took place whether (frequency 60 per sec.) or not (frequency 30 per sec.) neuromuscular transmission fatigue developed. The phenomenon was reversible. No significant change of muscular excitability was found when prolonged stim. at 60 per sec. led to renewed transmission (5th stage) following fatigue (4th stage). Complete curarization occurred without any change of the muscular electrical excitability. Curare, however, caused a decrease of excitability. Although prostigmin did not modify the muscular excitability, it caused an increase if injected after curare. While the response of muscles to single nerve volleys were repetitive after prostigmin, those to direct stimulation were single. The electrical theory of neuromuscular transmission fails to explain the 4th and 5th stages, the block of transmission produced by curare, and the repetitive character of the responses to nerve volleys after prostigmin.

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