NERVOUS MECHANISM OF RESPIRATION. 



343 



FIG. 154. 



Diagram of the Nervous Mechanisms of Respiration. (After Fick.) 

 sc. Centre for inspiratory movements, from which pass efferent channels, 

 represented by the continuous white line (o) to the inspiratory muscles rep- 

 resented by the diaphragm (D). EC. Centre for expiratory movements, 

 from which efferent channels (p) pass down the cord to the muscles of ?x- 

 piration, represented by the abdominal muscles (A). To both these centres 

 afferent impulses come (1) from the cerebral centres (a, 6, c, d) to check or 

 excite activity. These voluntary impulses may be called afferent as far as 

 the respiratory centres are concerned. From (2) the cutaneous surface, and 

 (3) the nose, impulses (e,f, g) arrive, which modify the action of the inspi- 

 ratory centre. From the (4) larynx (G) come checking impulses (h) to the 

 inspiratory, and exciting impulses (i) to the expiratory centre ; and, finally, 

 (5) from the lungs come both exciting and inhibiting impulses (k, I, m, n) 

 to both the expiratory and inspiratory centres, and by these channels the 

 rhythm of ordinary breathing is regulated. 



