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Simultaneous Intracellular Recording of a Lumbar Motoneuron and the Force Produced by its Motor Unit in the Adult Mouse In vivo
Published on: December 5, 2012
Motor unit action potential components and physiologic duration
D Dumitru1, J C King, W E Rogers
1University of Texas Health Science Center at San Antonio, Department of Rehabilitation Medicine, 78284-7798, USA.
Muscle & Nerve
|June 12, 1999
Summary
Motor unit action potentials (MUAPs) reveal a late far-field potential mirroring intracellular action potentials. This duration relates to muscle fiber length and intracellular action potential dynamics.
Area of Science:
- Neuroscience
- Physiology
- Biophysics
Background:
- Motor unit action potentials (MUAPs) are crucial for assessing neuromuscular function.
- Understanding the full duration and morphology of MUAPs, including far-field potentials, is important for accurate clinical interpretation.
- Previous studies have not fully elucidated the relationship between intracellular action potentials (IAPs) and extracellularly recorded MUAP components.
Purpose of the Study:
- To investigate the nature and duration of late far-field potentials in MUAPs.
- To correlate MUAP duration with intracellular action potential (IAP) morphology and muscle fiber length.
- To explain the observed MUAP findings using a leading/trailing dipole model.
Main Methods:
- Recording MUAPs from the biceps brachii muscle using monopolar needle electrodes at two distances.
- Averaging 2000-3000 MUAPs at high amplifier gains.
- Conducting computer simulations of MUAPs to model intracellular action potentials (IAPs).
Main Results:
- Recorded MUAPs exhibited a mean total duration of 39.6 +/- 4.6 ms.
- A late far-field potential with a mean duration of 23.8 +/- 4.1 ms was observed in the terminal segment of MUAPs.
- Computer simulations indicated that this far-field potential reflects the IAP's repolarization phase (~30 ms).
Conclusions:
- The physiologic duration of MUAPs is proportional to muscle fiber length and IAP duration.
- The late positive far-field potential represents the dissipation of the IAP at the musculotendinous junction.
- A leading/trailing dipole model can qualitatively explain these quantitative findings in MUAP recordings and simulations.
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