REFERRED PAIN 



191 



logical process stimulates the articular branches of the femoral 

 (anterior crural) nerve, but the pain of which the patient 

 complains is referred to the region of the knee, which also 

 receives branches from the same nerve (Fig. 73). 



It is by no means certain by what sequence of events a 

 referred pain is produced. Mackenzie, to whom we are 

 indebted for most of our knowledge on this subject, suggests 



***~~ 



FIG. 76. Diagram to explain a Viscero-sensory Reflex. 



The plain arrows indicate the path of afferent impulses from the viscus ; the 

 dotted arrows indicate the "overflow" stimulus. 



C. Cortex. 



P,n.r. Posterior nerve-root. 

 W.R.C. White ramus communicans. 



G.R.C. Grey ramus communicans. 

 Sy. G. Sympathetic ganglion. 

 V. Viscus. S. Skin. 



that abnormal afferent impulses may not only stimulate the 

 nerve cells for which they were originally intended, but may 

 " overflow " and so stimulate other nerve-cells in their neigh- 

 bourhood. The effect produced by this " overflow " stimula- 

 tion will be the same as if the cells had received an impulse 

 from the nerve-fibres with which they are associated. In both 

 methods of stimulation, the impulse which ascends to the cortex 

 is interpreted in the same way and, if the cells affected by the 

 "overflow" normally receive afferent stimuli from a cutaneous 



