High frequency discharge of a fraction (f) of motor unit action potential.
Two repetitive discharges, firing at 105 and 180 Hz, were evoked in muscles with chronic denervation. They were delayed following a motor unit action potential (M), and their maximum duration was 800 and 50 ms, respectively. The potential of both high frequency discharges was of low amplitude and short duration. It was considered to be a fraction (f) of the motor unit potential, and to depend on muscle fibres re-innervated by an axonal branch. The repetitive mechanism was tested by double stimulation. It seemed to be an ephaptic re-excitation of the axonal branch by a sprout rather than an ectopic trigger locus on the latter. The antidromic waves, associated with the repetitive discharges on the axonal branch, failed to be transmitted to the main axon. This failure, assimilated to a conduction block, was complete in the first case as M was not repetitive. It was intermittent in the second case as M was firing intermittently. Repetitive activity associated with 'terminal multifocal block' could be relevant to the fractional activation observed by others in some disease states.
Soichot
P
P
EEG-EMG Laboratory, Regional and University Hospital, Dijon, France.
Roth
G
G
D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D003714:Denervation; D003929:Diabetic Neuropathies / Q000503:physiopathology; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology*; D010507:Periodicity; D014459:Ulnar Nerve / Q000502:physiology