| Abstract: | Lumbar cord potentials evoked by electrical stimulation of the posterior tibial and sural nerves at the ankle were recorded with monopolar epidural electrodes, at T11-T12 level in 20 subjects and were compared with surface recorded potentials. Two quadriplegic patients with spinal section were included in this group. Curare was given in two cases. Xylocaine block of peripheral nerve was carried out in 4 cases. Double shock study was done in 5 cases. The lumbar cord evoked potentials show two successive components: a 'primary' negative-positive spike response with a latency of 19-35 msec, and the 'secondary' waves with latencies up to 200 msec. The 'primary' response is mainly produced by the afferent volley in the fibres of the dorsal roots and of their intramedullary prolongations. There is no evidence which suggests that it is correlated with presynaptic inhibition. The secondary components may be divided into the early and the late waves. The early waves (40-90 msec) are related to the polysynaptic activities from the afferent fibres of small diameters. The late waves are under the influence of supraspinal mechanism and may be related to long-loop reflexes. The clinical implications of these evoked potentials are discussed. |
