CHAPTER XXXVIII 

 THE CONTROL OF THE RESPIRATION 



The participation of such widespread groups of muscles in the respira- 

 tory act demands that some mechanism be provided to insure its adequate 

 control. With every inspiration, for example, the muscles of the alse 

 nasi act so as to cause dilatation of the nares, the vocal cords are ab- 

 ducted, and the intercostal muscles, along with the scalenes and the 

 diaphragm are contracting while the muscles of the abdominal wall are 

 relaxing; and all these events occur at exactly the proper time so as to 

 bring about the most efficient opening up of the thoracic cavity. Evi- 

 dently there must be some mechanism to insure this perfect control. This 

 is effected through the nervous system. 



THE RESPIRATORY NERVE CENTERS 



The efferent fibers to the various groups of muscle originate in their 

 respective motor neurons, which in most cases are situated in the gray 

 matter of the spinal cord. The harmonious action of these motor neu- 

 rons, or subsidiary centers, is brought about by the transmission to them 

 of impulses from a higher or master center placed in the medulla ob- 

 longata, the pathway of transmission between this master center and the 

 subsidiary centers being in the lateral columns of the spinal cord. 



The evidence that the chief respiratory center is in the medulla is fur- 

 nished by observing the effects produced on the respiratory movements 

 by serial destruction of the cerebrospinal axis from above downward. 

 By this method the approximate position of the center is found, its exact 

 location being then determined by punctiform destruction or stimulation 

 of the supposed locus of the center. If we destroy the cerebrum from 

 before backward, piece by piece, we shall find that no marked effect is 

 produced on the respirations until we arrive at about the middle of the 

 medulla, when immediate paralysis of the respiratory movements occurs. 

 If we now proceed to puncture various areas on the floor of the fourth 

 ventricle in another animal, we shall find an area called the noeud vital, 

 located about the tip of the calamus scriptorius, destruction of which 

 causes immediate cessation of respiration. It is believed that the center 

 resides in the group of nerve cells known to neurologists as the fasciculus 

 solitarius. It is bilateral. 



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