Our Nervous System 437 



The medulla presides over and controls the action of the 

 respiratory system, the contraction of arteries and the process of 

 swallowing. 



The spinal cord is an organ of nerve tissue lying within the 

 rings of the backbone. It connects with the brain and also, by 

 nerve branches, with all parts of the body. 



Reflex action is a response to an impulse brought to the spinal 

 cord by a sensory nerve, without direction from the brain. 



The conditions necessary to keep the nervous system in a nor- 

 mal state are fresh air, proper food, exercise and rest. 



Nervous force should be conserved. Some activities which 

 waste nervous energy are worry, undue excitement, loss of temper 

 and over-indulgence in pleasure. 



Self-control is essential. It enables the mind to direct all 

 activities of the body towards a useful end. 



It is necessary to avoid certain things that are likely to harm 

 the nervous system, such as excess of mental work, eye strain 

 and use of drugs. 



Use of alcohol, tobacco and other drugs is injurious to the 

 health of the nervous system. 



FACT AND THOUGHT QUESTIONS 



1. Tell how parts of the body cooperate in spading a garden ; in swim- 

 ming. 



2. Name the most important parts of the nervous system. 



3. Describe the structure of the brain. 



4. Describe the structure of the spinal cord. 



5. What is a neuron? 



6. Give the functions of the brain. 



7. What is reflex action? 



8. Discuss the importance of reflex action. 



9. Describe the structure of the sympathetic system. 



10. State the functions of the sympathetic system. 



11. Does loss of temper make you feel physically better, or worse? Why? 



12. Name some way in which you have wasted nervous energy in the last 

 day or so. 



13. Name several bodily habits that will tend to keep you "clear-headed." 



14. WTiy is exercise beneficial after severe study or examinations? Should 

 such exercise be light or heavy? 



