EXCITABILITY OF THE TURTLE AURICLE DURING VAGUS STIMULATION

Publisher Website
Google Scholar
Abstract
In 24 experiments on 13 turtles (each experiment including a number of tests of excitability for 3-7 hrs.) changes in rheobase, in chronaxie and in "least time" produced by vagus stimulation were made on the auricle, which was either rendered quiescent, slowed, or allowed to beat at a normal rhythm. Providing the region in contact with the stimulating electrode is directly inhibited and not merely arrested as a result of the cessation of activity elsewhere, vagus stimulation produces a definite rise in the threshold (rheobase) of excitation by the constant current; a slight or moderate shortening of the chronaxie, which is always associated with a rise in the rheobase; and a lengthening of the time required for excitation by a current of greater than rheobasic strength. The effects of acetyl choline are the same as those of vagus stimulation. Atropine eliminates the vagus effects on excitability. In the same heart the magnitude of the observed changes in excitability is roughly proportional to the degree of inhibitory weakening of the systoles. When different hearts are compared, the same fact usually holds. The changes in excitability were never observed in the absence of conspicuous inotropic action of the vagus on the auricle tested. If excitability be defined in terms of the quantity of energy required for excitation, then vagus stimulation decreases excitability.

This publication has 4 references indexed in Scilit: