384 



A YEAR IN SCIENCE 



outside world. Parts of our body must, receive impres- 

 sions from the outside world, and then these must be 

 communicated from them to other parts. This adjust- 

 ment and regulation of the parts of the body to each 

 other and to the outside world is the work of the 

 nervous system. 



Parts of nervous system. 



^vcv* 



Cell 

 Body 



Axon 



-Sheath 



Endings 



177. Diagram to show the 



structure of a neuron. 



The nervous system con- 

 sists of nerve centers and 

 nerves. The nerve centers 

 are the brain, the spinal 

 oor ^ an d smaller centers 

 called ganglia scattered in 

 different parts of the body. 

 From these nerve centers 

 nerves arise. These divide 

 a great many times and 

 their branches penetrate all 

 the organs and tissues of 

 the body. 



The nerve cell, The unit 

 of structure in the nervous 

 system is the nerve cell, or 

 neuron. This is not so 

 simple in structure as many 

 of the other cells in the 

 body. It consists of a large 

 cell from which there are 

 many projections called 

 dendrites. One of these 



