The functional organization of respiratory neurones: A review

Abstract

The classical work reviewed by Pitts and consolidated by stimulation, transec-tion and ablation experiments reviewed by Wang and Ngai,2 revealed a subdivision of medullary respiratory neurones into mutually inhibiting inspiratory and expiratory centres, Pontine, apneustic and pneumotaxic centres were thought to excite the inspiratory and expiratory centres respectively. The apneustic centre was presumed to be tonically active while the pneumotaxic centre was periodically active and generated respiratory rhythmicity with the aid of vagal afferents. Microelectrode techniques used to examine individual neurones by Burns and Salmoiraghi26amp;-28 and reviewed by Salmoiraghi,3 have led to a new theory of respiratory neuronal organization. As previously, mutually inhibitory populations of inspiratory and expiratory neurones form the basic medullary oscillator. These neurones are not located in centres but intermingled and apparently connected in self re-exciting chains. The oscillator is driven by chemoreceptor and lung afferents and also by the general medullary traffic. Pontine functions are not thought to be essential to its operation but as aiding the smooth transition from one respiratory phase to the next. Further microelectrode studies36amp;-38 have indicated the complexity of behaviour of respiratory neurones, and re-emphasized the importance of pontine neurones. Cohen30 has proposed a model of the functional organization of respiratory neurones which employs several subsidiary control loops acting upon the main oscillator, in order to account for these findings. It is argued, however, that the complex behaviour of individual respiratory neurones may be due to their varying degrees of excitation from the medullary environment, so that the model of Salmoiraghi and Bums is still appropriate. © 1972 Canadian Anesthesiologists.