CHAPTER XVIII 

 STRUCTURE AND PROPERTIES OF THE NERVOUS SYSTEM 



Divisions and structure of the nervous tissue Medullated nerve-fibres Non-medullated 

 nerve-fibres Gelatinous nerve-fibres (fibres of Remak) Accessory anatomical elements 

 of the nerves Branching and course of the nerves Termination of nerves in voluntary 

 muscles Termination of nerves in glands Modes of termination of sensory nerves 

 Corpuscles of Vater, or of Pacini Tactile corpuscles End-bulbs General mode of 

 termination of the sensory nerves Structure of the nerve-centres Nerve-cells Nissl's 

 granules The neuron Accessory anatomical elements of the nerve-centres Degen- 

 eration and regeneration of nerves Motor and sensory nerves Mode of action of the 

 motor nerves Associated movements Mode of action of the sensory nerves Physi- 

 ological differences between motor and sensory nerves Nervous excitability and conduc- 

 tivity Rapidity of nervous conduction Personal equation Action of electricity on 

 the nerves Law of contraction Electric current from the exterior to the cut surface 

 of a nerve Electrotonus, anelectrotonus and catelectrotonus. 



THE nervous system is anatomically and physiologically distinct from 

 all other systems and organs. It receives impressions made on the ter- 

 minal branches of its sensory portion, and it conveys stimulus to parts, 

 determining and regulating their actions ; but it gives to no tissue or 

 organ its special excitability or the power of performing its particular 

 office in the economy. The nervous system connects into a coordinated 

 organism all parts of the body. It is the medium through which all 

 impressions are received. It animates or regulates all movements, vol- 

 untary and involuntary. It regulates, also, secretion, nutrition, calorifi- 

 cation and all the processes of organic life. 



In addition to its action as a medium of conduction and communica- 

 tion, the nervous system, in certain of its parts, is capable of receiving 

 impressions and of generating a stimulating influence, or force, peculiar 

 to itself. As there can be no physiological connection or coordination 

 of different parts of the organisms without nerves, there can be no 

 unconscious reception of impressions giving rise to involuntary move- 

 ments, no appreciation of impressions, general, as in ordinary sensation, 

 or special, as in sight, smell, taste or hearing, no instinct, volition, thought 

 or even knowledge of existence, without nerve-centres. 



DIVISIONS AND STRUCTURE OF THE NERVOUS TISSUE 



The nervous tissue presents two great divisions, each with distinct ana- 

 tomical as well as physiological differences. One of these divisions is 



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