THE FUNCTIONAL UNIT OF THE NERVOUS SYSTEM 



581 



with a single receptor, the efferent paths originating from a common 

 center. These effectors may or may not act in unison; i.e. they may 

 be alhed or antagonistic in their function. If the former case, the re- 

 action simply becomes more diversified and complex, but continues to 

 present a perfectly co-ordinated character. An antagonistic behavior 

 on their part, however, must lead to a disconcerted reaction which, 

 in most cases, can only be prevented by inhibiting the action of one of 

 the effectors. Conversely, two receptors may be associated with only 

 one effector (Z)). If stimulated simultaneously, the impulses arising 

 in these receptors, will have a tendency to interfere with one another 

 until the more effective of the two finally succeeds in gaining the com- 

 mon path to the effector. It may also happen that these impulses, if 



C 



^ 



1 1 



1% 



K 



^ 



£ E 



sf 



E 



^ i^ 



^ 



y 



\ 



^ V 



D 



y 





Fig. 290.- 



RE R R R 



-Diagram Illustrating the Joining of Reflex Circuits. 

 R, Receptor; C, center; E, effector. 



simultaneously elicited, reinforce one another so that the response 

 becomes much greater than it would have been if only one of them had 

 been received. Reflex arcs may also be combined into the form 

 represented by Fig. 290, E. We observe here that the successive 

 circuits are brought into close relation with one another by connecting 

 paths, so that the stimulus applied to one of them may skip either to the 

 same or to neighboring effectors, or both. In this way, much more 

 complicated reflexes may be elicited which, although for the most part 

 allied, may at times assume an antagonistic character. 



It will be pointed out in a subsequent paragraph that the spinal 

 cord, in combination with the spinal nerves and those apportioned to 

 the sympathetic system, is especially well adapted for reflex action. 

 In fact, as the cord really consists of a large number of reflex centers 



