Relative Coordination between Neuron Firing and Generation of a Motor Program in the Human CNS, pp. 265-295
Authors: Giselher Schalow
Abstract: Using surface electromyography (sEMG) from patients with spinal cord injury and Parkinsonís disease it is shown that FF-type motor units fire at a rate of around 10Hz with one motor unit potential, and FR-type motor units fire at a frequency of 4 to 5Hz with approximately 3 motor unit potentials per impulse train. Such oscillatory firing is compared with the oscillatory firing of α1, α2, and α3-motoneurons, innervating FF, FR, and S-type muscle fibres, which fire at approximately 10Hz, 4 to 7Hz and 1Hz, respectively, as measured earlier from human motoneuron axons with the single-nerve fibre action potential recording method; repeated firings with impulse trains consisted of 1, 2-5, and 20-50 action potentials per impulse train respectively. In spinal cord injury patients, FF-type motor units, firing for medium activation at around 10 Hz, are observed to fire up to 43Hz for increasing activation (exercising at increasing load). During coordinated movement, a motor program burst is shown to be generated by recruiting partly motor units to fire oscillatory for the burst time. Moreover, FF-type motor units are shown to fire with relative phase and frequency coordination. The coordination was between motor unit firings of the same muscle and between muscles of the right and left arm. It was found earlier with the single-nerve fibre action potential recording method that α and γ-motoneurons and muscle spindle afferents fired in relative coordination. There is therefore indication that relative phase and frequency coordination is an integrative mechanism for the self-organization of the neuronal networks of the human central nervous system (CNS).