CHAPTER VII 

 REFLEXES 



_In the previous chapter we had chiefly in view the 

 part of the nervous system which directly controls the 

 skeletal muscles. The statement was made that the 

 fibers which establish this connection are called efferent 

 (Latin efferre, to bear away). There are fibers in even 

 greater number which provide for the conveyance of 

 impulses into the central nervous system from localities 

 external to it. These, as has been said, are called afferent 

 afferre, to bear toward). They are often called sensory. 

 An objection may be raised against the term sensory 

 inasmuch as it suggests that there is conscious recogni- 

 tion of the arrival of all the impulses that traverse these 

 fibers. This cannot possibly be maintained. 



Receptors. Afferent fibers are said to lead from 

 receptors to the brain or the cord. A receptor is any 

 mechanism by which external forces can give rise to 

 nerve-impulses. The name may be applied to the 

 simple ending of a nerve fiber that lies exposed to pres- 

 sure in the skin or it may refer to such elaborate organs 

 as the eye and the ear. The word external which has 

 been used must be applied with regard to the central 

 nervous system. The position of a receptor may be 

 internal as judged by ordinary standards. Thus there 

 are nerve-terminals in the peritoneum which may be 

 stimulated by tension and give rise to pain. Move- 

 ments of the head may affect receptors in the depths 

 of the temporal bone. Yet it remains true that we 

 are usually concerned with receptors at the surface of 

 the body. The word sense-organ may be used as a 

 synonym for receptor though it is likely to suggest more 

 readily the highly specialized features of the equipment. 



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