320 PHYSIOLOGY CHAP. 



stimulated simultaneously the extensors are inhibited and the 

 flexors of both sides are thrown into contraction. 



Inhibition of a spinal centre through other centres probably, 

 according to Sherrington, plays a great part in the co-ordination of 

 the spinal acts. In fact, his researches show that the contraction 

 of any group of muscles is usually accompanied by the inhibition 

 of the antagonist group. The tension of the muscle in consequence 

 of its contraction mechanically excites its sensory apparatus 

 (inusculo-tcridinous organ of Golgi) and thus reflexly depresses the 

 tone of the antagonist muscle. On faradising the central end of 

 the nerve of the femoral biceps of the cat the effect of this 

 stimulation on the extensor muscles of the knee is shown by their 

 elongation and the temporary diminution of the patellar reflex. 



FIG. 184. Myograms of weak tonic contraction of m. extensor communis of toes. (Verworn.) 

 The arrows indicate the times at which there is reflex inhibition of tone after crushing the 

 antagonist muscles. The curves are reduced to . 



If the flexor muscle of the leg is detached from its insertion and 

 then stretched or compressed, there is, as with electrical stimulation, 

 a relaxation of the extensor muscle of the knee and a weakening 

 of the knee-jerk. To confirm these effects, which Sherrington calls 

 reciprocal innervation of antagonist muscles, Verworn performed 

 the following experiment on the dog : he isolated the branch of 

 the peroneal nerve by which the m. extensor lougus communis of 

 the foot is innervated, detached this muscle from its insertion, and 

 connected it with a recording apparatus, after fixing the limb by 

 a plaster bandage. On stimulating the nerve at regular intervals 

 of one second, he obtained a tracing of approximately equal con- 

 tractions. On pinching the flexor muscles with a large forceps 

 during this periodical stimulation he obtained a temporary fall in 

 the level of the contractions, which indicates a reflex depression of 

 the tone in the muscle due to the mechanical excitation of its 

 antagonist (Fig. 184). 



