338 



THE NERVE SYSTEM 



FlG - 119 



Neuralgia cells of brain shown 

 by Golgi's method. A. Cell with 

 branched processes. B. Spider-cell 



\vilh unhfitnclicd processes. (After 

 Andriezen.) (From Schfifer's 7?.\-.sv//- 

 tials of I 



of cells glia cells and glia 

 fibers. There are two varie- 

 ties of the latter ependy- 

 mal cells and astrocytes. 

 The supporting tissue ele- 

 ments of the brain, etc., 

 do not possess the power 

 of developing or conveying 

 nerve impulses; they are 

 spoken of as non-neural. 



The Origin of Nerves. 

 Efferent nerves, those 

 which conduct impulses 

 to the periphery, muscles, 

 glands, bloodvessels, etc., 

 in response'to stimuli from 

 the brain and spinal cord, 

 originate in the nerve cells 

 of the gray substance of 

 these structures, and the 

 axones are prolonged to 

 form the nerve fibers. 

 Nerves emerge from the 

 brain and spinal cord as 

 single rounded cords. They 

 may possess only a single 

 root of origin or two roots 

 widely apart from each 

 other, yet each of the two 

 roots may be different in 

 function, as seen in the 

 spinal nerves, the anterior 

 root being motor or effer- 

 ent, the posterior sensor or 

 afferent. The point at 

 which a single nerve root 

 leaves the brain or spinal 

 cord is called the super- 

 ficial origin of a nerve; 



