XXXV. THE NERVOUS SYSTEM 



General Functions of the Nervous System. — We have seen that, 

 in the simplest of animals, one cell performs the functions neces- 

 sary to its existence. In the more complex animals, where groups 

 of cells form tissues, each having a different function, a ner- 

 vous system is developed. The functions of the nervous system are: 

 (1) the providing of the man with sensation, by means of which he gets 

 in touch with the world about him; (2) the giving to the human being 

 a will, a provision for thought; (3) the connection of organs in different 

 parts of the body so that they act as a united and harmonious whole. 

 Cooperation in word and deed is the end attained. We are all 

 familiar with examples of the cooperation of organs. You see 

 food; the thought comes that it is good to eat; you reach out, take 

 it, raise it to the mouth; the jaws move in response to your will; 

 the food is chewed and swallowed; while digestion and absorption 

 of the food are taking place, the nervous system is still in control. 

 The nervous system also regulates pumping of blood over the body, 

 respiration, secretion of glands, and, indeed, ever\^ bodily function. 



Divisions of the Nervous System. — The control of a number of 

 activities for the attainment of a definite end is the function of the 

 nervous system in the lowest as well as the highest of animals. 

 In the vertebrate animals, the nervous system consists of two 

 divisions. One includes the brain, spinal cord, the cranial and 

 spinal nerves, which together make up the cerebrospinal nervous 

 system. The other division is called the sympathetic nervous sys- 

 tem. The activities of the body are controlled from nen^e centers 

 by means of fibers which extend to all parts of the body, there 

 ending in the muscles. The brain and spinal cord are examples 

 of such centers, since they are largely made up of nerve cells. 

 Small collections of nerve cells, called ganglia, are found in other 

 parts of the body. These nerve centers are connected, to a greater 

 or less degree, with the surface of the body by the nerves which 



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