Motoneuron resting potentials in spinal shock

Abstract

The resting membrane potential of cells in the lumbar segment of the spinal cord was measured in cats before, during, and after the cord was functionally blocked. Blocking was achieved by cooling with o C brine passed through a copper tube surrounding the cord at the midthoracic level. Of those units identifiable by antidromic stimulation as motoneurons, 95% underwent a hyperpolarization of from 2 to 6 mv (mean 3.6 ± .2 mv) when the cord was blocked. A group of units that could not be identified as motoneurons underwent a hyperpolarization of from 2 to 8 mv (mean 3.7 ± .5 mv). The physiologic derangement in spinal shock is a hyperpolarization of motoneurons. Such hyperpolarization is thought to result from the removal of random synaptic bombardment by nerve endings, either directly or indirectly activated from more cephalad regions, which normally keep the cell in a slightly hypopolarized state.