LECTURE VII. 



NERVOUS SYSTEM. 



Function. — The peculiar function of the nervous system is 

 to control the various organs and systems of the body, and com- 

 pel them to work in harmony. The peculiar property of nerve 

 tissue is irritability. The nervous system is composed of nerve 

 centers, nerve trunks, nerve fibers, and nerve cells. 



A nerve center is composed of ganglion cells, nerve fibers, 

 connective tissue, and blood vessels. The function of a nerve 

 center is to receive and dispose of impressions which may be 



CAB 



FIG. 15. NERVE CELL AND NERVE FIBER, 



A. Nerve Cell with Several Poles. One pole continues as a medullated 

 nerve fiber. A, Primitive sheath; B, medullary sheath; C, axis cylinder. 



2. Medullated Nerve Fiber. A, Primitive sheath; B, medullary sheath; 

 C, axis cylinder; D, node; E, nerve corpuscle. 



brought to it, to connect nerve fibers, and in the case of the fore 

 brain to originate conscious impulses. 



A nerve fiber is composed in some cases of a central fiber 

 surrounded by one or two protecting sheaths ; in other cases, of 

 the central fiber only. Nerve fibers conduct impulses between 

 the various tissues and organs, and the nerve centers. 



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