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 (Vll witli SiNcial I'lilis. due poli' (iiiiliiuus as a medullated 

 nerve fibti-. A, Primitive shratli; B, nu'diillary sheatli; C, axis cylinder. 



2. Medullatid N<rvc Fiber. A, Primitive sheath; B, medullary sheath; 

 C, axis cylinder; D, n<Kl<; E, nerve corpuscle. 



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

 brain to originate conscious impulses. 



A nerx'c 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 orgai'.s, and the nerve centers. 



