. SECTION II. 



THE PHYSIOLOGY OF THE CENTRAL 

 NERVOUS SYSTEM. 



CHAPTER VI. 



STRUCTURE AND GENERAL PROPERTIES OF THE 

 NERVE CELL. 



The Neuron Doctrine. Since the last decade of the nineteenth 

 century the physiology of the nervous system has been treated 

 from the standpoint of the neuron. According to this point of 

 view, the entire nervous system is made up of a series of units, 

 the neurons, which are not anatomically continuous with each 

 other, but communicate by contact only. It has been taught also 

 that each neuron represents from an anatomical and physiological 

 standpoint a single nerve cell. The typical neuron consists of 

 a cell body with short, branching processes, the dendrites, and a 

 single axis cylinder process, the axon or axite, which becomes a 

 nerve fiber, acquiring its myelin sheath at some distance from the 

 cell. According to this view, the peripheral nerve fibers are simply 

 long processes from nerve cells. Within the central nervous system 

 each neuron connects with others according to a certain schema. 

 The axon of each neuron ends in a more or less branched " terminal 

 arborization," forming a sort of end-plate which lies in contact 

 with the dendrites of another neuron, or in some cases with the 

 body of the cell itself, the essentially modern point of view being 

 that where the terminal arborization of the axon meets the dendrites 

 or body of another neuron the communication is by contact, the 

 neurons being anatomically independent units. It is usually ac- 

 cepted also as a part of the neuron doctrine that the conduction 

 of a nerve impulse through a neuron is always in one direction, 

 that the dendrites are receiving organs, so to speak, receiving a 

 stimulus or impulse from the axon of another unit and conveying 

 this impulse toward the cell body, while the axon is a discharging 

 process through which an impulse is sent out from the cell to reach 

 another neuron or a cell of some other tissue. The neuron, so 



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