Electro-physiology . electrophysiolog02bied Year: 1896-98 ix ELECTRICAL EXCITATION OF NERVE 19:1 As regards the break excitation, it should be observed that it requires stronger currents (here as everywhere) than the make effect, and may, like this last, produce opposite changes of form in the muscle under certain conditions. In consequence of the inferior strength of the opening stimu- lus, however, it only excites the muscle in the majority of cases, and seldom reaches sufficient proportions to inhibit a pre-existing tonus. But if in such a case the exciting action of the current fails to f
Electro-physiology . electrophysiolog02bied Year: 1896-98 ix ELECTRICAL EXCITATION OF NERVE 19:1 As regards the break excitation, it should be observed that it requires stronger currents (here as everywhere) than the make effect, and may, like this last, produce opposite changes of form in the muscle under certain conditions. In consequence of the inferior strength of the opening stimu- lus, however, it only excites the muscle in the majority of cases, and seldom reaches sufficient proportions to inhibit a pre-existing tonus. But if in such a case the exciting action of the current fails to find expression, the effects of stimulation both at make and at break of the circuit may consist in a transitory relaxation of the tonically contracted muscle: the curve then presents two depressions, one beginning at closure, and disappearing only during the passage of the current, the other less considerable—corresponding with the break of the exciting circuit (Fig. 199). In view of the double, partly inhibitory, partly exciting effect of stimulating the two muscles of the crayfish claw with the constant current, the important question arises whether— under the presumption of pure polar action of current—the two effects, at make on the one hand, at break on the other, proceed from the same electrode, or whether there is an antagonism between the respective discharges of excitation and inhibition. It has already been stated of the atonic adductor muscle that the order of excitatory effects corresponds throughout with Pfliiger's law ; both on applying very strong currents, and after excluding the influence of the central electrode by partially killing the nerve, the descending current takes effect at make, the ascending current at break only of the circuit. Since in the first case—owing to the enormous resistance in the exciting circuit, and low density within the part traversed— the current must be of very considerable intensity in order to obtain the third stage
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