.224 BIOLOGY AND HUMAN LIFE 



Study of diseased or injured brains has established the fact 

 that each portion of the cerebral cortex is concerned with some 

 special feelings, ideas, or movements. In the diagram (Fig. 113) 

 are indicated some of the localizations of brain function that 

 have been determined in such studies. 



All the afferent and efferent neurons related to reflexes are 

 also connected with the brain by way of the spinal cord (see 

 Fig. 114). When you burn your finger you withdraw your hand, 

 and then you feel the pain (see Fig. 1 10) . If you waited for ac- 

 tion until you were aware that something had happened, it 

 would in most cases be too late. The cerebrum has to do with 

 conscious and voluntary action. It cannot control the reflexes, 

 and in most cases it is not aware of them. Many of our activi- 

 ties and movements are unrelated to the cerebrum ; but every 

 thought, every conscious desire, and every deliberate or pur- 

 poseful action depends upon impulses starting from the gray 

 matter of the brain or leading through this gray matter. 



THE NERVOUS SYSTEM 



1. Irritability 



General (all protoplasm) ; special (special organs or tissues) 



2. Stimulus and response 



Depends upon general irritability of protoplasm 

 Special structure for response to stimuli (reflex arc) 



Receptor (afferent path) 



Connector (association path) 



Effector (efferent path) 

 Kinds of effectors 



Muscles ; glands ; nerves 



3. Nerve structure 



Cell body ; axon ; dendrites ; synapse 



4. The brain 



General structure 



Tissues Connections 



Cortex Spinal cord 



Association fibers Cranial nerves 



5. Control 



Movements and processes that are automatic and uncontrolled 

 Movements and processes that are controlled 



