COORDINATION AND CONTROL: (1) THE NERVOUS SYSTEM 



121 



parts contains a number of nerve tracts of different function, which 

 serve as communicating lines to and from various portions of the central 

 nervous system. The medulla contains the centers for the regulation of 

 many autonomic activities, such as the heartbeat, respiration, swallow- 

 ing, visceral movements, the dilation and constriction of the blood ves- 

 sels, glandular secretion, and perspiration. It is from this part of the brain 

 that the vagus nerves extend to the heart and viscera. 



MID-BRAIN LEVEL 



sensory receptor 



adjustor neuron 



SPINAL CORD 



Fig. 7.9. The mechanism of second-level response, (a) Axon; (d) dendrite. (Modified from 

 Gates, Elementary Psychology, by permission The Macmillan Company.) 



The gray cortex of the cerebellum is a center for the correlation of a 

 host of afferent impulses (from the muscles, joints, and tendons and from 

 the static balance, touch, and pressure receptors, etc.) with the complex 

 of efferent impulses that are required to maintain the body's posture and 

 unconscious adjustments to its environment. It is not certain how inde- 

 pendent some of these synapses may be from cerebral control; but it is 

 clear that in normal functioning, even voluntary movements that are 

 initiated in the cerebral cortex involve a host of relays and connections 



