PFLUGER'S LAWS: HOW WE TRANSITION INTO PAIN 

Edward Friederich Wilhelm Pfluger, German Physiologist, 1829-1910
 

Stage One

LAW OF UNILATERALITY
You hurt where you injured yourself. 
 

Stage Two 

LAW OF SYMMETRY
If stimulus to the nervous system is sufficiently increased, you start to hurt in similar muscles on the side other than the one you injured, but you still hurt most where you injured yourself. 
 

Stage Three 

LAW OF INTENSITY
As stimulus to the nervous system increases, the side you didn't injure now hurts as much as the side of the initial injury. 
 

Stage Four

LAW OF RADIATION
With the continued increase of stimulus to the nervous system, the nervous impulses travel up the spine activating reactions through centrifugal nerves coming from cord segments higher up. In essence, areas of old injuries become reactivated. 
 

Stage Five

LAW OF GENERALIZATION
With intense stimulus to the nervous system, the impulses are propagated to the medulla oblongata, which becomes a focus from which stimuli radiate to all parts of the cord, causing a general contraction of all muscles in the body.