Nature and origin of automatic activity in the respiratory center of the frog

Summary

Stimulation of interneurons at the level of entrance of the vagus fasciculus near the fasciculus solitarius provokes local contraction of only “inspiratory” muscles, while stimulation of the interneurons at the level of the exit of the II spinal root, also near the dorsal portion, causes local contraction of only “expiratory” muscles. In normal automatic activity the functional characteristics of the “inspiratory” and “expiratory centers” is identical with that of the efferent region. With the exclusion of the impulsation from the aortic receptors, when automatism ceases, the rheobase in the “inspiratory center” assumes a double value, while chronaxie is increased 4–10 times, accomodation constant (λ) is cut nearly in half. At the same time the functional characteristics of both the “expiratory” center and the efferent area approach the initial one. Hence a conclusion was drawn that the automatic excitation is being formed only in the region of the “inspiratory center”.