314 ADVANCED PHYSIOLOGY 



organ which it is to supply. In this way, impulses started 

 by the brain neurons eventually reach the muscles to be 

 moved or the tissue to be innervated. 



REFLEX ACTIONS 



We have already noted that a message coming into the cord 

 from the body may, on occasion, be switched off onto side 

 branches of the fibre it was traversing, jump from its terminal 

 arborations to the dendrites of a neighboring neuron, and go 

 outward over the anterior root of a spinal nerve without 

 immediately going to the brain. There are some further 

 aspects of these reflex actions which should be noted, for an 

 almost infinite number of movements and minor functions 

 of the body, as well as many very important ones, are thus 

 performed. 



Probably every person makes more movements uncon- 

 sciously than consciously. If his attention were especially 

 called to each one of his actions, they would immediately 

 become matters of all-absorbing concern to him, and would 

 take so much of his time that he would be able to attend to 

 nothing but the simplest activities. Suppose, for example, 

 that one had to think definitely about the contraction of each 

 muscle concerned in walking, whenever he took a step; sup- 

 pose he had to deliberate about the contraction of every 

 muscle concerned in winking every time he moved his eyelids; 

 suppose that every time his clothing touched him at any 

 point, a message were sent to his centre of consciousness in 

 the brain. The nervous energy required would be almost 

 incalculable, and the maintenance and regulation of life 

 would be impossible. 



We have already found that the essential peculiarity of a 

 reflex movement is that it is performed without the media- 

 tion of any of the conscious centers of the brain. These re- 

 sponses can indeed be obtained in animals from which the 



