EFFECTS OF POSTERIOR ROOT SECTION ON THE ACTIVITY OF SOME MUSCLES IN MAN

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Abstract
Past studies of the effects of posterior root section on movements of limbs in experimental animals and man and on respiratory movements in the cat are reviewed. New observations, including electromyographic (E. M. G.) and respiratory recordings, are reported on 3 patients following unilateral section of various cervical and thoracic posterior root segments which deafferented the diaphragm, intercostals and levator scapulae muscles. Absence or diminution in electrical activity, related to lowered functional activity in motor centers in the cord, was found after operation. The recovery process was attributed to 3 possibilities: (1) increased sensitivity of motor neurones to chemical transmitters liberated at their presyn-aptic terminals; (2) afferents from synergic muscles entering the cord via an intact route restoring excitability; and (3) new synapses due to sprouting of collaterals and preterminals.