REFLEX ACTION 213 



withdrawn the following actions take place. The heal 

 stimulus affects the nerve endings in the finger and that 

 stimulus is carried to the spinal cord. If this were all that 

 occurred, the finger would burn, because this stimulus and 

 the nerve fibers over which it travels have no control over 

 the muscles. The removal of the linger calls into play an- 

 other set of nerve cells, — the cells which have their fibers 

 ending in the hand and arm. All of these changes take 

 place involuntarily, and the reaction to the stimulus is 

 known as reflex action. Specific names are used in de- 

 scribing these several changes ; the nerve fibers which 

 connect the skin with the spinal cord and brain are 

 called afferent (affer-ent: Latin, ad, to ; fero, to carry ) 

 fibers because the stimulus always travels toward the 

 brain. 



Their function is sensory, for they carry the stimulus to 

 the brain. The fibers which connect the muscle with the 

 brain or spinal cord are the efferent (ef'fer-ent : Latin, 

 ex, from ; fero, to carry) fibers, because they carry their 

 message away from the central nervous system. Their 

 function is motory. In the special instance we are study- 

 ing, the heat stimulus causes the spinal cord to send a 

 special message to the muscles of the finger, so that the 

 latter is removed from the stove. 



This is a typical illustration of the simplest way in 

 which the nervous system works, but in most reflex 

 actions there are other results. After the finger has been 

 removed from the hot stove by reflex action, we soon 

 realize that the skin is burned, the realization oniim; 

 through the smarting sensation. This second stimulus 

 has been carried to the brain, and we are now conscious of 

 the stove, heat, burn, etc. If there were no afferent nerve 

 fibers, the individual could not experience any pain when 

 hurt. 



