INTEGRATION OF ACTION WITHIN THE REFLEX ARC 939 



may be elicited coincides exactly with that for the inhibition of the antag- 

 onistic muscles, as do also the kinds and strengths of stimuli which are effec- 

 tive in each case. The inhibition of antagonists may consequently be 

 considered a part of the same reflex which excites the agonists to contrac- 

 tion. 



It is impossible to demonstrate any trace of inhibition of the skeletal 

 muscles by stimulation of their motor nerves, thus indicating that in- 

 hibition is dependent upon the nerve center. Furthermore, since inhibition 

 occurs along with contraction of the antagonistic muscle, we must assume 



Fig. 239. Record from myograph connected with the extensor muscle of the knee. During 

 the time marked by the lower signal, the skin of the opposite foot was stimulated, thus causing 

 the crossed extension reflex. While still maintaining this stimulation, faradic shocks were ap- 

 plied to the skin of the foot of the same side (as indicated by the upper signal), with the result 

 that immediate inhibition of the contracted extensor occurred. (From Sherrington.) 



that the afferent impulse on entering the spinal cord divides into 

 two branches, one going to one motor neuron so as to excite it, the other 

 to another neuron so as to inhibit the tonic stimuli which it is con- 

 stantly sending to the muscles (Fig. 240). According to this assumption 

 the effect of impulses carried over each branch depends on the nature of 

 the synapse which these make with the motor neurons of the antagonistic 

 groups of muscles. 



Since the seat of the inhibition is in the nerve center, it is to be ex- 

 pected that impulses transmitted from other parts of the nervous system 



