528 



RESPIRATION 



CHAPTER XLII 

 THE NERVOUS REGULATION OF RESPIRATION 



The Respiratory Center and Its Nervous Connections. The nerv- 

 ous mechanism concerned in respiration, consists of a center and 

 different efferent and afferent conducting paths. On the efferent side 

 the nerve paths always remain the same, because the same muscles 

 are constantly at work expanding the lung and producing related motor 

 effects. The impulses generated in the respiratory center, reach these 

 different effectors by way of their respective nerves, and hence, the 

 efferent half of the respiratory arc is formed by the different nerves 

 innervating the muscles ordinarily concerned in 

 respiration. On the afferent side, on the other 

 hand, conditions are not so simple, because the 

 character of the respiratory movements is subject 

 to variations in consequence of a very large number 

 of sensory impressions. Practically any one of 

 the receptors, internal as well as external, may be 

 the recipient of impressions which are eventually 

 relayed to the respiratory center, where they incite 

 an alteration in the rate and depth of the respira- 

 tions. In accordance with this brief preliminary 

 statement, it should be evident that the destruction 

 of the efferent paths must entail an immediate 

 arrest of the respiratory movements, because the 

 impulses generated by the respiratory center, are 

 then no longer able to reach the respiratory mus- 

 cles. An arrest of respiration must also follow the 

 destruction of the center itself, for the reason that 

 the stimuli upon which the contraction of these 

 muscles depends, then fail to materialize. Con- 

 trary to these results, the division of the afferent 

 path does not stop the respiratory movements, 

 because it does not destroy the rhythmic discharges from the center. 

 It is to be noted, however, that the movements are then wholly de- 

 pendent upon the automatic activity of the center and can no longer 

 be varied by afferent impulses arising in other parts of the body. 



The Location of the Respiratory Center. In accordance wiih the 

 experiments of Lorry, 1 Le Gallois 2 and Flourens, 3 the respiratory cen- 

 ter is situated in the medulla oblongata at the level of the apex of the 

 calamus scriptorius. More recent experiments by Volkmann and 



1 Memoires pro's, a 1'acad. des Sciences, i, iii, 366. 



2 Exper. sur la principe de la vie, Paris, 1812. 



3 Rech. exp. sur la systeme nerveaux, Paris, 1824. 



FIG. 262. THE 

 NERVOUS REGULATION 

 OF RESPIRATION. 



C, respiratory 

 center is under the 

 control of afferent 

 impulses (.A) from 

 different receptors 

 (ft). On the efferent 

 side (E) it is in con- 

 nection with the dif- 

 ferent muscles of res- 

 piration (M). 



