Regional gravity field modeling using airborne gravity data

Earth Observation and Space SystemsAerospace Engineerin

Microscopic and macroscopic volume conduction in skeletal muscle tissue, applied to simulation of single-fibre action potentials

Extracellular action potentials of a single active muscle fibre in a surrounding of passive muscle tissue were calculated, using a microscopic volume conductor model which accounts for the travelling aspect of the source, the structure of skeletal muscle tissue and the electrical properties at the level of single muscle fibres. Owing to the capacitive properties of the muscle fibre membranes this inhomogeneous model is frequency dependent. The results of these calculations were compared with results obtained with a macroscopic homogeneous, frequency-independent version of the model. Close to the excited fibre the extracellular action potentials of both descriptions differ in their sensitivity to variations in the intra- and extracellular conductivities. It is demonstrated that within about 300 μm the muscle fibre membrane influences the amplitude as well as the timing of the peaks of the extracellular action potential. Both volume conduction descriptions result in almost the same single-fibre action potential at large radial distances from the excited fibre. These model results are of primary interest for the quantitative interpretation of single-fibre electromyograms recorded close to an active fibre, as for example in clinical fibre-density measurements

Sensitivity of the amplitude of the single muscle fibre action potential to microscopic volume conduction parameters

A microscopic model of volume conduction was applied to examine the sensitivity of the single muscle fibre action potential to variations in parameters of the source and of the volume conductor, such as conduction velocity, intracellular conductivity and intracellular volume fraction. The model results show that the sensitivity to the intracellular and extracellular conductivity depends on the distance from the source. The action potential amplitude is strongly influenced by the intracellular volume fraction. In this frequency-dependent model the amplitude is influenced by the conduction velocity to a smaller degree than predicted by previous studies, which use a noncapacitive homogeneous volume conductor model

Model of electrical conductivity of skeletal muscle based on tissue structure

Recent experiments carried out in our laboratory with the four-electrode method showed that the electrical conductivity of skeletal muscle tissue depends on the frequency of the injected current and the distance between the current electrodes. A model is proposed in order to study these effects. The model takes into account the structure of the tissue on the scale of individual fibres. It discerns three main components with respect to electrical properties: (a) extracellular medium with electrical conductivity σe; (b) intracellular medium with electrical conductivity σi; (c) muscle fibre membrane with impedance Zm. The model results show an apparent frequency dependence of the electrical conductivity of skeletal muscle tissue, as well as the way the conductivity is affected by the length the current is conducted