342 



PHYSIOLOGY 



of the same side and inhibitor for the extensor muscles of the same side and 

 for the flexor muscles of the opposite side. 



The ascending branches of the nerve fibre in the same way will have 

 endings which, while inhibitor for the greater number of other possible 

 reflex changes, will be excitor in a slight degree for certain efferent neurons 

 whose action is allied to that of the primary reflex. The diagram shows 

 also that the contraction of the flexor muscle, set up as the result of stimu- 



-Fio. 171. Diagram indicating connections and actions of two afferent spinal 

 root cells a and a' in regard to their reflex influence on the extensor and flexor 

 muscles of the two knees. The sign + indicates an excitatory effect, the 

 sign an inhibitory effect. (SHERRINGTON.) 



lating a, itself initiates a secondary reflex process from muscle up the nerve 

 fibre a and back again to the muscle by the efferent neuron. This muscular 

 afferent nerve also has central terminations of two signs excitor to itself 

 and inhibitor to the antagonistic muscles. For the sake of clearness the 

 diagram omits a number of other channels coming from other regions of 

 the cord, or from other efferent nerves, the sign of which would be negative, 

 i.e. which would tend to inhibit the activity of the whole reflex arc. 



We see therefore that from every sensitive point on the surface of the body 

 impulses can be initiated which will set into action whole chains of neurons, 

 and will have a widespread influence throughout the central nervous system. 

 It is important to u<>t> that the efferent path innervating, say, the flexor 

 muscles of one side is common to many reflexes. It is used, for instance, by 

 mutually antagonistic reflexes such as the scratch reflex and the flexor or 



