282 



COORDINATION AND SENSATION 



of the nervous system with all parts of the 

 body, no amount of study of its gross struc- 

 tures reveals the nature of its connections 

 or suggests its method of operation. In- 

 sight into the real nature of the nervous 

 s y stern is obtained only through a study of 

 its minute structural elements. These, in- 

 stead of being called cells, a*s in the case of 

 the other tissues, are called neurons. The 

 use of this term, instead of the simpler one 

 of nerve cell, is the result of recent ad- 

 vances in our knowledge of the nervous 

 system. 1 



The neurons are in all respects cells. 

 They differ widely, however, from all the 

 other cells of the body and are, in some 

 respects, the most remarkable of all cells. 

 j , They are characterized by minute exten- 

 branches sions, or prolongations, which in some in- 

 J\^ stances extend to great distances. Though 



' , T.. the neurons in certain parts of the body 

 tic. 1 20. Dia- f J 



gram of a mon-ax- differ greatly in form and size from those 

 onic neuron (great- in other parts of the body, most of them 

 ly enlarged except as may be i nc i u d e d in one or the other of 



to length). Thecen- . . 



... , . ., two classes, known as mon-axonic neurons 



tral thread in the 



axon is the axis cyl- and di-cixonic neurons. 



Mon-axonic Neurons. Neurons of this 



III b 



1 Almost to the present time, physiologists have described the nervous system as 

 being made up of two kinds of structural elements which were called nerve cells 

 and nerve fibers. The nerve cells were supposed to form the ganglia and the fibers 

 to form the nerves. Recent investigators, however, employing new methods of 

 microscopic study, have established the fact that the so-called nerve cell and nerve 

 fiber are but two divisions of the same thing and that the nervous system is made up 

 of, not two, but one kind of structural element The term "neuron" is used to 

 denote this structural element, or complete nerve cell. 



