NERVOUS SYSTEM 



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 communica- 

 tion is believed to be 

 established between 

 them; that is, an im- 

 pulse may travel from 

 one cell to another 

 through its dendrites. 



External stimuli 

 have their origin in 



FIG. 182. 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.) 



a nerve ending in 



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 



