NERVOUS SYSTEM 



363 



Structure of a neurone or nerve cell. — A neurone, 

 commonly called a nerve cell, consists of a cell body and its 

 processes. There are 

 usually several short 

 processes called den- 

 drites and one long 

 process or axon with 

 a central fiber or axis 

 cylinder. Dendrites 

 are usually branched 

 like the limbs of a 

 tree. The axon be- 

 comes the nerve fiber 

 of the nerves. Im- 

 pulses pass to and 

 from the cell body 

 along the axis cylinder 

 of the axon. The 

 dendrites of each cell 

 body surround or 

 come into close con- 

 tact with the dendrites 

 of other cell bodies 

 so that commimica- 

 tion is believed to be 

 established between 

 them; that is, an im- 

 pulse may travel from 

 one cell to another Fig. 182. 

 through its dendrites. 



External stimuli 

 have their origin in 

 a nerve ending in 



Diagram ■ showing relation of 

 centers of language and their principal 

 associations. A, auditory center; V, visual 

 center; M, motor speech center; E, motor 

 writing center; O. O., intellectual center. 

 (After Grasset.) 



some part of the body, as in the retina of the eye. Visual 

 stimuli are carried along the axis cylinders of the nerves to the 



