title: Discharge variability and physiological properties of human masseter motor units.
abstract: Intramuscular electrodes were used to study discharge variability in motor units of human masseter whose physiological properties were determined using spike-triggered averaging. Subjects voluntarily controlled the mean firing rate of a selected motor unit at 10 Hz for 15 min of continuous activation. Discharge variability was assessed at the beginning and end of this period. In 81% of units, the discharge variability at a mean interspike interval (ISI) of 100 ms increased after 15 min of continuous activity. There was a wide range of discharge variability within the population of masseter units studied, but no significant correlations were found between initial discharge variability and recruitment threshold, twitch tension or time-to-peak tension (TTP). There was, however, a significant correlation between motor unit fatigability and its initial discharge variability. This represents a link between the motoneuron and the functional properties of the muscle fibers in innervates.
authors.affiliation: Department of Physiology, University of Adelaide, Australia.
authors.forename: M A
authors.initials: MA
authors.lastname: Nordstrom
authors.forename: T S
authors.initials: TS
authors.lastname: Miles
mesh_terms: D000293:Adolescent; D000328:Adult; D004056:Differential Threshold; D004594:Electrophysiology; D006801:Humans; D008406:Masseter Muscle / Q000294:innervation*; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction; D011999:Recruitment, Neurophysiological