The early phase of reflex activity after spinal cord transection

Of 36 spinal monkeys, six had a local anesthetic applied to the distal stump of the cord at intervals of 1–68 min after transection. Reflex responses fell consistently below the control level, (recorded between time of transection and that of local anesthesia of the stump of the cord). Latencies of tendon reflexes are abnormally prolonged after spinal transection. Reflexes of Macaca mulatta fall into three groups: those that are strongly facilitated by collaterals of ascending neurons; those that are weakly facilitated; and those that are not facilitated thereby. The first class includes hip and ankle flexion in response to a nocuous stimulus, the ankle jerk, and the hamstring jerk; the second category contains the knee jerk and adductor jerk; the third, tremulous adduction and flexion of digits in response to pinch of the sole. We concluded that the evanescent exhaltation of reflexes after spinal transection is due to antidromic activity of ascending neurons ephaptically excited by evoked potentials in adjacent fibers.