The bioelectrical source in computing single muscle fiber action potentials

Abstract

Generally, single muscle fiber action potentials (SFAPs) are modeled as a convolution of the bioelectrical source (being the transmembrane current) with a weighting or transfer function, representing the electrical volume conduction. In practice, the intracellular action potential (IAP) rather than the transmembrane current is often used as the source, because the IAP is relatively easy to obtain under experimental conditions. Using a core conductor assumption, the transmembrane current equals the second derivative of the IAP. In previous articles, discrepancies were found between experimental and simulated SFAPs. Adaptations in the volume conductor slightly altered the simulation results. Another origin of discrepancy might be an erroneous description of the source. Therefore, in the present article, different sources were studied. First, an analytical description of the IAP was used. Furthermore, an experimental IAP, a special experimental SFAP, and a measured transmembrane current scaled to our experimental situation were applied. The results for the experimental IAP were comparable to those with the analytical IAP. The best agreement between experimental and simulated data was found for a measured transmembrane current as source, but differences are still apparent.

Motor unit action potential components and physiologic duration

“…It is precisely this IAP morphology that is traditionally modeled to generate simulated MUAPs. 30,38 However, amphibian 25,29 and mammalian 37 (including human 24 ) IAPs reveal a repolarization phase in excess of 20 ms, referred to as the "slow afterpotential." It is postulated that the complete IAP configuration must be considered to model more accurately the MUAP's physiologic duration.…”

“…1A). 36,38 This IAP morphology is monophasic positive and displays a relatively rapid repolarization phase, returning to the resting membrane potential within approximately 4 ms of potential onset. Inspection of both mammalian 24,36,40 and amphibian 2,29 IAPs reveals an IAP similar to that mathematically modeled, but with a more prolonged terminal repolarization phase, approaching 30 ms (Fig.…”

Surface electromyogram signal modelling

“…2a), a smoother analytic function proposed by ROSENFALCK (1969) ( Fig. 2b) or an empirically measured waveform (VAN VEEN et al, 1993). The triangular lAP is referred to as the 'tripole' model because it produces three impulses of current during propagation.…”

Single muscle fiber discharge transformations: Fibrillation potential to positive sharp wave

“…1C). 19,25 Its onset-to-peak magnitude was defined as 75 mV to conform to an experimentally obtained IAP and served as the IAP template for modeling myotonic discharges. 18,22 The second IAP was recorded from a 7-day denervated rat hemidiaphragm and was modeled by combining the above innervated IAP's mathematical representation with a ''best fit'' (Sigma Scan Image/ Plot and TableCurve 2D, Jandel Scientific, San Rafael, CA) expression for the denervated IAP's terminal hyperpolarization phase (Fig.…”