254 THE NERVOUS SYSTEM 



pressions to and motor impulses from the brain must all pass 

 through by this route. 



As a reflex nerve center the medulla also resembles the cord, 

 though impressions reflected through this organ are frequently 

 much less simple than those reflected through the cord. Reflex 

 action in the medulla is dependent on (3), to be noticed now. 



3. The most important center presiding over coordinated 

 movements is that for respiration. The encephalon may be cut 

 away down as far as the medulla, and life will continue for a cer- 

 tain time. It is al so ti ue that the medulla itself may be gradually 

 cut away from above downward until a certain point is reached, 

 when respiration suddenly ceases. Likewise the spinal cord may 

 be cut away upward till this point is reached, when the same re- 

 sults will follow. This is the true respiratory center, and is situ- 

 ated at the site of origin of the vagi. Its destruction is followed 

 by an immediate suspension of respiration and consequent death 

 by asphyxia, though there is no manifestation of the distress 

 usually accompanying this condition. The sense of want of air is 

 simply lost. There is one of these centers for each side, but they 

 act synchronously, being connected by commissural fibers. 

 Probably the usual mode of stimulation of the respiratory center 

 is by afferent impressions, but it may also be stimulated directly, as 

 by deoxygenated blood. Mutilation of the medulla, on account 

 of the presence of this center, is followed by the nearest approach 

 to instantaneous death, and the respiratory center has, therefore, 

 been called the "vital spot," though death from any cause can- 

 not be instantaneous. 



Some other reflex centers are for deglutition, sucking, secretion 

 of saliva, vomiting, coughing, sneezing, dilatation of the pupil, se- 

 cretion of sweat, secretion of glycogen, etc. Typical of these is 

 the reflex act of sneezing, in which case impressions are conveyed 

 to the medulla by the nasal branches of the fifth nerve. 



Additional centers in the medulla are those which preside over 

 inhibition and acceleration of the heart, vaso-motor centers for the 



