Impaired Coordination between Oscillatory Firing FF and FR-Type Motor Units in Parkinsonís Disease and Patients with Spinal Cord Injury, pp. 501-517
Authors: Giselher Schalow
Abstract: In a previous contribution it was shown that, in the rather physiologic functioning human central nervous system (CNS), oscillatory firing motor units coordinate their firing so as not to fire synchronously. In this paper I will show that, in spinal cord injury and in Parkinsonís disease patients in whom coordination is impaired, some motor units fire spontaneously oscillatory according to the muscle fibre type. Additionally, in Parkinsonís disease patients numerous oscillatory firing motor units synchronized their firing resulting in rhythmic muscle movement and shaking of body parts (tremor). Using surface electromyography (sEMG) it can be shown that tremor in different muscles is partly coordinated. Motor program bursts during coordinated low-load movements were structured in Parkinsonís disease patients by rhythmic firing at ≈ 10Hz (firing frequency of FF-type motor units) and 5Hz (frequency of oscillatory firing FR-type motor units and frequency of tremor). In patients with partially injured spinal cord, motor bursts during high-load exercising were structured with the oscillation frequencies of FR and FF-type motor units and higher frequencies. Since α1 and α2-motoneurons which innervate FF and FR-type muscle fibres respectively, were reported earlier to fire oscillatory in the isolated spinal cord, in Parkinsonís disease patients rhythmic firing of motor units and tremor is thought to primarily originate in the spinal cord rather than in the basal ganglia.