THE AUTONOMIC SYSTEM 221 



neuron of the cerebrum. As the child thinks whether he shall 

 brush the teeth up and down or across, whether his mouth should 

 be open or closed, whether he should lean over the basin or not, 

 connections are set up among association neurons. Finally, he 

 comes to a decision. An impulse is sent along an efferent axon 

 down the spinal cord and into the muscles of the arm which are 

 the effectors. The actual brushing of the teeth is the motor 

 response. The correct response was consciously made. This is 

 an act of the third level involving the cerebrum. After the teeth 

 have been brushed a number of times, the decisions and the asso- 

 ciations are no longer necessary. While the act was conscious, 

 inhibitions in the nervous system blocked certain paths of con- 

 duction between the sensory stimulus and the motor response. As 

 the act was repeated, time after time, these inhibitions disappeared, 

 and the act was easier to perform. The more times the impulse 

 passed over the pathway of discharge, the less was the resistance 

 to it. After this reaction was learned a synapse was set up be- 

 tween the afferent and eft'erent pathways, leaving out some of the 

 association neurons. In some habits the pathway is essentially the 

 same, but consciousness is omitted. It has become automatic and 

 has descended to the second or possibly the first level. It is now 

 an acquired automatic activity involving no thought and is com- 

 monly called a habit. Habits are frequently defiaed as acts which 

 were first done in a typically voluntary way, but after sufficient 

 repetition they are done in a comparatively reflex way. Memory 

 is most important in changing conscious acts into habits. 



Importance of the autonomic system in nerve activities. The 

 internal organs, in general, are under the control of the autonomic 

 nervous system. The autonomic system controls the contractions 

 and relaxations of the smooth muscles. It regulates glandular ac- 

 tivities and heart action. Emotions activate the autonomic sys- 

 tem. If an emotion such as fear or anger accompanies a reflex act, 

 habit, or a conscious act, the autonomic system enters into the 



