FUNCTIONS OF THE MEDULLA OBLONGATA. 481 



The afferent cells give origin to fibers which pass to the cerebral 

 cortex. Around both groups of cells, the afferent or sensor cranial 

 nerves terminate in tuft-like expansions. In a subsequent section the 

 origin, course, and distribution of the various cranial nerves will be 

 considered. But as the function of the nerve is but to transmit 

 energy from the cell of which it constitutes a part, the function 

 ascribed to it may without impropriety be transferred to the cell 

 itself. 



Since it is by means of nerve-cells and their associated fibers that 

 many important functions of organic life are initiated and maintained, 

 it would naturally be expected from its. extensive nerve connections 

 that this region of the nerve system plays an extensive role in this 

 respect. As the accomplishment of these functions requires the 

 cooperation and coordination of a number of separate but related 

 structures, it is evident that there must exist in the medulla and pons 

 a number of coordinating mechanisms consisting of nerve-cells and 

 nerve-fibers which are associated in various ways for the accomplish- 

 ment of definite functions. To such a coordinating mechanism the 

 term " center" has been given: e. g., respiratory, cardiac, deglutitory, 

 etc.* 



As centers for reflex activities. Experimentation has shown 

 that the medulla and pons contain a number of such centers, the 

 more important of which are as follows : 



1. A cardiac center, which exerts (i) an accelerator influence over the 



heart's pulsations through nerve-fibers emerging from the spinal 

 cord in the roots of the first and second dorsal nerves and reach- 

 ing the heart through the sympathetic nerve] (2) an inhibitor 

 or retarding influence on the action of the heart through efferent 

 fibers in the trunk of the pneumogastric nerve. (See page 295.) 



2. A vaso-motor center, which regulates the caliber of the blood- 



vessels throughout the body in accordance with the needs of the 

 organs and tissues for blood, through nerve-fibers passing by 

 way of the spinal nerves to the walls of the blood-vessels. (See 

 page 327.) 



3. A respiratory center, which coordinates the muscles concerned in 



the production of the respiratory movements. (See page 



3 8o.) 



4. A mastication center, which excites to activity and coordinates the 



muscles of mastication. (See page 157.) 



5. A deglutition center, which excites and coordinates the muscles 



* By the term center as here employed is meant a collection of nerve-cells and 

 nerve-fibers occupying an area of greater or less extent, though its exact anatomic 

 limits may not be 'accurately defined. That an area may merit the term center, it 

 is necessary that its stimulation should increase, its destruction should abolish or 

 impair, functional activity. 

 3* 



