INFLUENCE OF NERVOUS SYSTEM. 185 



Influence of the Nervous System in Respiration. 



Like all other functions of the body, the discharge of which 

 is necessary to life, respiration must be essentially an involun- 

 tary act. Else, life would be in constant danger, and would 

 cease on the loss of consciousness for a few moments, even in 

 sleep. But it is also necessary that respiration should be to 

 some extent under the control of the will. For were it not 

 so, it would be impossible to perform those voluntary respira- 

 tory acts which have been just enumerated and explained, as 

 speaking, singing, straining, and the like. 



The respiratory movements and their regular rhythm, so far 

 as they are involuntary and independent of consciousness (as 

 on all ordinary occasions they are), seem to be under the ab- 

 solute governance of the medulla oblongata, which, as a ner- 

 vous centre, receives the impression of the " necessity of 

 breathing," and reflects it to the phrenic and such other motor 

 nerves as will bring into co-ordinate and adapted action the 

 muscles necessary to inspiration. 



In the cases of voluntary respiratory acts, we may believe 

 that the brain, as well as the medulla oblongata, is engaged in 

 the process ; for we have no evidence of the mind exercising 

 either perception or will through any other organ than the 

 brain. But even when the brain is thus in action, it appears 

 to be the medulla oblongata which combines the several re- 

 spiratory muscles to act together. In such acts, for example, 

 as those of coughing and sneezing, the mind first perceives the 

 irritation at the larynx or nose, and may exercise a certain 

 degree of will in determining the actions, as e. g., in the taking 

 of the deep inspiration which always precedes them. But the 

 mode in which the acts are performed, and the combination of 

 muscles to effect them, are determined by the medulla oblon- 

 gata, independently of the will, and have the peculiar char- 

 acter of reflex involuntary movements, in being always, and 

 without practice or experience, precisely adapted to the end or 

 purpose. 



In these, and in all the other extraordinary respiratory 

 actions, such as are seen in dyspnoea, or in straining, yawning, 

 hiccough, and others, the medulla oblongata brings into 

 adapted combination of action many other muscles besides 

 those commonly exerted in respiration. Almost all the muscles 

 of the body, in violent efforts of dyspnoea, coughing, and the 

 like, may be brought into action at once, or in quick succes- 

 sion ; but more particularly the muscles of the larynx, face, 

 scapula, spine, and abdomen, co-operate in these efforts with 

 the muscles of the chest. These, therefore, are often classed 



