CHAPTER XXVIII. 

 GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM. 



ANATOMICAL SKETCH. 



The nervous system is the apparatus by which the distant 

 parts of the body are kept in constant relationship with one 

 another, so that a change of state of any one organ is communi- 

 cated to and may set up corresponding changes in remote parts 

 of the system. It is made up of two varieties of tissue, both of 

 which possess special vital properties. The one which is com- 

 posed of thread-like strands of protoplasm nerve fibres connect 

 together the elements of the other group, the nerve corpuscles, 

 which form either peripheral or central terminals. Nerve fibres 

 are then simply special conducting agents, having at one ex- 

 tremity a special terminal or nerve cell for sending impulses, and 

 at the other extremity other cells for receiving the same. These 

 terminal organs, between which the nerve fibres pass, are the 

 agents which determine the direction the impulse is to travel along 

 the nerve. The sending organ is sometimes at the peripheral 

 end of the nerve, and the receiver in the nerve centres, as in the 

 case of an ordinary cutaneous nerve, which carries impulses from 

 the skin to the brain ; or these duties of the terminal organs 

 may be reversed, as in the case of the nerves conveying impulses 

 from the brain to the muscles. 



The former kind of nerves are called afferent or centripetal, and 

 the latter efferent or centrifugal. Nerves are capable of carrying 

 impulses in either direction, as has been proved by cutting the 

 afferent lingual and the efferent hypoglossal nerves, and causing 

 the proximal end of the former to unite with the distal end of 

 the latter, which is distributed to the muscles of the tongue. 

 When the union has taken place, a stimulus applied on the effer- 

 ent portion causes the muscle to move. 



Any piece of protoplasm can conduct impulses, as is seen in 

 the rapid transmission of an impulse in animals and textures 



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