390 A YEAR IN SCIENCE 



drawn away from the pin. In such an action the 

 current is carried to the spinal cord, or to some gan- 

 glion, and from there currents are sent out which stimu- 

 late the muscles. This is called a reflex action. 



Reflex actions. These actions are produced without 

 the consent of any conscious center of the brain. The 

 impulse may go to the brain, but not to cells where 

 conscious activity occurs. Reflex actions, such as the 

 movements of the internal organs, the heart, stomach, 

 or the glands, are involuntary. These are due to inter- 

 nal stimuli. Many of our responses to external stimuli 

 are also reflex: the winking of the eyelids, walking, 

 removing the hand from a hot object, and many others. 

 These actions are performed quickly, and they also 

 relieve the brain of a great deal of work. All of our 

 time would be needed to attend to only the simplest 

 activities necessary for life, if they were all done 

 consciously. 



Voluntary action. We have just learned that the 

 peculiarity of a reflex movement is that it is performed 

 without the action of the conscious center, the cere- 

 brum. All actions which do come from the use of the 

 cerebrum and which are thus under the control of the 

 will are voluntary. 



If food is placed before us, impulses are sent from 

 the eye to the visual center of the cerebrum. From 

 there messages may be sent to motor centers in the 

 brain, from which in turn impulses may go to the 

 muscles of the arm causing us to pick up some of the 



