CHAPTEE XIII 



THE NEKVOUS CONTROL OF RESPIRATORY RHYTHM 



CONTENTS. 1. Motor nerves to respiratory muscles and smooth muscle cells of 

 bronchi. 2. Bulbar respiratory centres and their localisation. 3. Spinal respira- 

 tory centres. 4. Cerebral respiratory centres. 5. Each of these centres results 

 from the association of an inspiratory and an expiratory centre, which function 

 rhythmically and alternately. 6. Automatic regulation of normal respiratory 

 rhythm, by afferent pulmonary fibres of vagus. 7. Influence exerted on respiratory 

 rhythm via the cerebral tracts and sensory nerves in general. 8. Phenomena 

 consequent on the separation of the bulb from the brain and spinal cord. 9. 

 Dyspnoea and its different forms. 10. Eupnoea or normal quiet respiration. 11. 

 Experimental apnoea from artificial respiration with the bellows. 12. Foetal apnoea, 

 and the analogous forms of experimental apnoea that can be produced in the adult. 

 13. Voluntary, as compared with experimental apnoea. 14. Apnoea produced 

 by continuous ventilation in birds. 15. Periodic respiration, or Cheyne-Stokes 

 phenomenon. 16. Physiological theory of respiratory rhythm. Bibliography. 



THE previous chapter shows that the respiratory processes are 

 highly complex, owing to the number of muscles, anatomically 

 very distinct, and even remote from each other, which co-operate 

 in them. Their efficacy in determining the rhythmical dilatation 

 and constriction of the thoracic cavity, and consequent pulmonary 

 ventilation, which are indispensable to life, is entirely due to co- 

 ordination, i.e. to the harmonious association and sequence of the 

 contractions of the individual inspiratory and expiratory muscles. 

 If, for example, the external intercostals were to contract before 

 the scaleni, or if the diaphragm became active along with the 

 internal intercostals, no adequate renewal of pulmonary air would 

 be obtained except with a useless expenditure of energy. 



Since the rhythmical activity of respiration results from the 

 co-ordinated functions of many and very distinct muscles, it cannot 

 be founded (as that of the heart may possibly be), on a physio- 

 logical property inherent in the muscles, but must necessarily 

 depend (as the facts prove clearly) upon the rhythmical co- 

 ordinating function of complex nervous processes, which are the 

 subject of the present chapter. 



I. The nervous mechanisms on which the respiratory rhythm 

 depends are as follows : 



(a) Motor nerves to the individual muscles which take part in 

 the inspiratory or expiratory movements ; 



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