CHAPTER XV 

 THE NERVOUS SYSTEM 



PART I 

 THE NEURONE AND THE NERVOUS IMPULSE 



The functions of the nervous system are to co-ordinate 

 the activities of the different organs of the body and to 

 bring the body into relation with its environment. 



The cells of which the nervous system are composed are 

 distinguished by possessing in an exalted degree two pro- 

 perties, irritability or the capacity to respond to a stimulus, 

 and conductivity or the capacity to transmit a disturbance 

 arising at any point in the cell with great rapidity through- 

 out the whole cell. Out of these two properties arise 

 others — the capacity to store impressions and to associate 

 them together — properties upon which depend the more 

 complex mental processes. 



THE NEURONE 



The nervous system is made up of a chain of nerve-cells 

 or neurones, each of which consists of a cell-body and 

 one or more processes. These processes are of two kinds, 

 axons and dendrons (or dendrites). The cell-body is the 

 enlarged part of the neurone which contains the nucleus. 

 It is the meeting-place of the processes if more than one 

 exist, and if only one process exists it is the part at which 

 the neurone comes into anatomical contact with the 



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