In order to observe the damaged nerve successively, we used superficial magnetic stimulation motor evoked potential (MEP) in the pathological model of chronic compressed nerve of the cervical nerve roots of cats. We synthesized various change of the pathomorphology of the nerve damaged to different degrees, and discussed the relationship between the MEP and the pathomorphologic change of chronic compressed nerve roots. The results showed that the initial pathologic change of nerve with myelin was degeneration of myelin shealth. The MEP of the nerve also showed increased latency and dispersed wave forms. After that the axon of the demylinated nerve degenerated, splitted and had a peripheral Wallerian Degeneration. The MEP showed an increased latency along with decreased amplitude. The degree of the MEP's change accompanyed with pathologic change. So we believe that the magnetic compressed nerve. It has some reference value in figuring out the damage by analysing factors.

To determine whether the pathological changes caused by injury to the spinal cord can be correlated with values obtained by the Magnetic Motor Evoked Potential (MEPs) technique, we studied spinal cords from 41 adult cats who were divided into 4 groups. The groups ranged from normal cats whose spinal cords were not compressed, to slightly, moderately and severely injured. MEPs were recorded before compression and in 30 minutes, 6 hours, 1 week, 2 week and 4 week after the compression unit was installed. Pathological changes with increased pressure were seen in blood vessels, nerve cells and fibers, Nissl substance and the central canal. A reversal of pathological changes was observed in slight or moderate injury during the 4 weeks of the experiment. Extensive injury, however, caused irreversible changes in the nerve cells with loss of motor function. The latency of MEPs at 30 minutes and 6 hours in the slightly injured group was 0.37 and 0.38 times greater than the baseline and returned to normal levels in 4 weeks. In the moderately injured group, the latency was increased 0.77 and 0.81 times and in the severely injured 1.32 and 1.36 times over the baseline. Recovery in the second group was partial and not at all in the severely injured. Thus, there appears to be good correlation between observed pathological changes, motor functions and MEPs.