PHYSIOLOGY OF THE NERVOUS SYSTEM 321 



way the nervous system adjusts the circulation to suit the conditions of 

 temperature outside of and within the body and, in so doing, maintains 

 the normal body temperature. 



Summary. The nervous system is able to control, co- 

 ordinate, and adjust the different organs of the body 

 through its intimate connection with all parts and through 

 a stimulus (the nervous impulse) which it supplies and 

 transmits. Nervous impulses, excited by external stimuli, 

 follow definite paths and cause activity in the different 

 parts of the body. All such pathways are through the 

 central nervous system. In reflex action the impulses 

 are mainly through the spinal cord, but to some extent 

 through the bulb, pons, and midbrain. In voluntary 

 action they pass through the cerebrum a condition that 

 leads to important modifications in the results. The 

 cerebrum, in addition to controlling the voluntary move- 

 ments, is able to establish the necessary conditions for 

 secondary reflex actions, such as walking, writing, etc. 

 Although certain of the divisions of the nervous system 

 exercise special functions, all parts of it are closely 

 related. 



Exercises. i. Give the function of each of the parts of a neuron. 



2. State the purpose of the nervous impulse. 



3. Show that the exciting cause of bodily action is outside of the 

 nervous system and, to a large extent, outside of the body. 



4. Describe the arrangement that enables stimuli outside of the 

 body to cause action within the body. 



5. Describe a reflex action and show how it is brought about. 



6. Distinguish between afferent, efferent, and intermediate neurons. 



7. Draw diagrams showing the impulse pathways in voluntary and 

 in reflex action. 



8. What purposes are served by the sympathetic neurons ? 



9. Describe the method of control of the circulatory and digestive 

 processes. How do reflex actions protect the body ? 



