CHAPTER XV 

 NERVOUS CONTROL OF THE RESPIRATORY APPARATUS 



276. The movements of respiration may go on in ordi- 

 nary quiet breathing without consciousness and without 

 volition, but they are also, in a measure, under voluntary 

 control not wholly so, for it is impossible to commit 

 suicide by holding the breath. 



277. The Respiratory Center and Nerves (Fig. 107). A 

 certain restricted area in the medulla oblongata is recog- 

 nized as the respiratory center, and there are believed to 

 be other such centers lower down in the spinal cord. Nerv- 

 ous impulses pass from the center down the spinal cord, 

 and thence by the anterior roots of many of the spinal 

 nerves to the plexuses which those nerves form. By com- 

 municating branches from these plexuses connection is 

 made with the spinal ganglia of the sympathetic system, 

 and with the tenth and eleventh cranial nerves. From 

 these various sources motor fibers pass on to the numerous 

 muscles concerned in respiration. That which supplies 

 the diaphragm is the phrenic nerve, which is traced back 

 to the three or four upper pairs of spinal nerves. 



If the spinal cord be divided below the fourth pair of 

 spinal nerves, the diaphragm will continue to act, but the 

 intercostal muscles will be paralyzed. If the cord be cut 

 just below the medulla oblongata, all respiratory movement 

 of the chest ceases ; and if that small portion of the medulla 



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