FUNCTIONS OF NERVOUS SYSTEM 321 



mind of the student, of the interactions of different parts of the 

 sympathetic system. 



These are the processes which must go on more or less continu- 

 ously. Some may be suspended temporarily, as gland secretions, 

 or digestion, or the formation of excretions, but they never entirely 

 cease without causing the death of the individual. 



SUMMARY 



The sympathetic nerves supply all involuntary muscles, the 

 coats of blood-vessels and the cells of secreting glands. They are 

 the nerves of unconscious life, as the cerebro-spinal nerves are the 

 nerves of voluntary and conscious life. 



SUMMARY OF THE FUNCTIONS OF THE NERVE SYS- 

 TEM AS A WHOLE 



We have now concluded the study (briefly) of the entire nerve 

 system, and we have seen how intimately its various parts are con- 

 nected. Only through a knowledge of these connections can the 

 functions of the system be understood. 



It must be remembered that all parts of the head and body 

 have at least two central representations. 



Sensory nerves (representing visceral muscle, certain mucous 

 membranes, etc., and sense organs), enter the cord and proceed as 

 far as the posterior horns, whence another cell body and its axon 

 receive and carry the impulse to the cortex of the brain. 



Motor cortical cells of the brain prolong their axons (nerve fibers) 

 only as far as the cord (the medulla oblongata is the upper portion 

 of the cord). There they meet certain other cells in the anterior 

 horns, where their message is taken to be carried by these second 

 axons to skeletal muscles. 



Different parts of the spinal cord are associated one with 

 another by conduction fibers, and the cord is connected with the 

 brain above by many more, running upward or downward through 

 the medulla and pons. (On the inferior surface of the brain we 

 see these fibers as crura or peduncles of the cerebrum and cere- 

 bellum; they are finally connected with the gray cells of the 

 cortex.) 



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