title: Motor unit action potential components and physiologic duration.
abstract: Motor unit action potentials (MUAPs) recorded from the same motor unit at two distances along the biceps brachii muscle with monopolar needle electrodes at high amplifier gains (20 microV/division) and averaged 2000-3000 times reveal total potential durations of 39.6 +/- 4.6 ms. In addition, the terminal segment for each of these two MUAPs contained a late far-field potential with a mean duration of 23.8 +/- 4.1 ms. Computer simulations of MUAPs suggest that this long-duration positive far-field mirrors the true morphology of the intracellular action potential (IAP), which is monophasic positive, possessing a terminal repolarization phase approaching 30 ms. This investigation suggests that the MUAP's physiologic duration is directly proportional to the muscle fiber length and the IAP's duration, which becomes manifest as a positive far-field potential when the IAP encounters the musculotendinous junction and slowly dissipates. The leading/trailing dipole model is used to explain qualitatively this study's quantitative clinical and computer simulation findings.
authors.affiliation: University of Texas Health Science Center at San Antonio, Department of Rehabilitation Medicine, 78284-7798, USA.
authors.forename: D
authors.initials: D
authors.lastname: Dumitru
authors.forename: J C
authors.initials: JC
authors.lastname: King
authors.forename: W E
authors.initials: WE
authors.lastname: Rogers
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000328:Adult; D003198:Computer Simulation; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000502:physiology*; D013997:Time Factors