Motor unit action potential components and physiologic duration

✍ Scribed by Daniel Dumitru; John C. King; William E. Rogers

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 165 KB
• Volume: 22
• Category: Article
• ISSN: 0148-639X
• DOI: 10.1002/(sici)1097-4598(199906)22:6<733::aid-mus10>3.0.co;2-6

✦ Synopsis

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.