CYCLIC CHANGES IN THE RESPIRATORY CENTERS, REVEALED BY THE EFFECTS OF AFFERENT IMPULSES

Publisher Website
Google Scholar
Abstract
Progressive changes in the respiratory centers of anesthetized cats during inspiration and expiration were revealed by stimulating the superior laryngeal nerves and recording electrically the impulses discharged by single phrenic motoneurones. One or 2 volleys of afferent impulses immediately after the 1st impulse discharged by a motoneurone at the start of inspiration slightly delayed the 2d impulse. The delay of the 2d impulse increased progressively with number of afferent volleys, up to a critical number, at which the delay abruptly increased many-fold. When afferent impulses were initiated later in inspiration, a sufficient number sometimes abruptly stopped the motoneurone activity; sometimes a few motor impulses were discharged following the afferent impulses before inspiration stopped prematurely. The threshold number of afferent volleys required to stop inspiration declined linearly throughout inspiration. A few volleys of afferent impulses during expiration delayed the start of the next inspiration, the delay being less the earlier in expiration the afferent impulses were initiated. The delay was reduced more by 1-second advance in timing of the stimuli in animals with short expiratory pauses than in animals with longer pauses. The delay was about equally reduced by advancing the stimuli from the end to the start of expiration, in all prepns., regardless of the duration of expiration. These findings are explained by assuming that the respiratory center is influenced by an as-yet-undefined state somewhere within it, which is developed progressively during natural inspiration and subsides gradually during expiration. Activity of inspiratory neurones in the center is assumed to stop when this state attains a certain level and to resume when another, lower, level is reached. The state may receive contributions from afferent impulses over the vagus nerves, but it is certainly also developed by other factors. During persistence of the central state developed by afferent nerve stimulation there was no corresponding reduction in frequency of discharge from phrenic motoneurones. This suggests that the central state is not an inhibitory state associated with the inspiratory cells in the respiratory centers, but may be an excitatory state at the central expiratory neurones.

This publication has 7 references indexed in Scilit: