Quantitative analysis of single muscle fibre action potentials recorded at known distances

In vivo records of single fibre action potentials (SFAPs) have always been obtained at unknown distance from the active muscle fibre.\ud \ud A new experimental method has been developed enabling the derivation of the recording distance in animal experiments. A single fibre is stimulated with an intracellular micropipette electrode. The same electrode is used thereafter for labelling with an auto-fluorescent dye, Lucifer Yellow. In this method there is no use of chemical fixation. The tissue structure is kept as well as possible. In cross-sections the fluorescent fibre is seen and its position is quantitized with respect to the tip of one or more recording wire electrodes.\ud \ud Morphometric data, such as the recording distance and the fibre cross-sectional area, are used for the interpretation of parameters of the SFAPs (peak-peak amplitude, time between the first positive and negative peaks). The present results show that within 300 μm recording distance is not as dominant for the SFAP shape as expected.\ud \ud The method offers also a direct check of the relation between the muscle fibre; diameter and the conduction velocity of the action potential. In the present small set of data there is no simple linear relationship

In vivo magnetomyograms of skeletal muscle

Magnetomyography (MMG) is a new noninvasive technique inspired by the magnetoneurographic method of J.P. Wikswo (IEEE Trans. Biomed. Eng., Vol.BME-30, p.215-21, 1983). MMG is used to detect action currents in a muscle, which is immersed in a highly conducting fluid. The detection coil is of a toroidal shape, with the muscle passing through the center of the coil. For a long muscle which fits tightly in the toroid, it is to be expected that magnetic fields correspond almost completely to the intracellular longitudinal (axial) currents in active muscle fibers. An experimental setup with specific coils for rat and mouse skeletal muscles was developed. It is sensitive enough to detect currents from single motor units. The technique can be used to record stimulated twitch activity in live muscle as a function of force level, coil position along the muscle, temperature, etc. By simulating the response with a finite-element forward model, it is possible to calculate action currents under various experimental condition

Breakdown and recovery of thin gate oxides

Breakdown events are studied in varying test set-ups with a high time resolution. Often a partial recovery from breakdown is observed\ud within a few ms. Parameters such as device area, stress conditions and parasitic elements prohibit the recovery if they result in a high system impedance. The results suggest the existence of a highly conductive path that can be annihilated during breakdown

Single fibre action potentials in skeletal muscle related to recording distances

Single muscle fibre action potentials (SFAPs) are considered to be functions of a bioelectrical source and electrical conductivity parameters of the medium. In most model studies SFAPs are computed as a convolution of the bioelectrical source with a transfer function. Calculated peak-to-peak amplitudes of SFAPs decrease with increasing recording distances. In this paper an experimental validation of model results is presented. Experiments were carried out on the m. extensor digitorum longus (EDL) of the rat. Using a method including fluorescent labelling of the active fibre, the distance between the active fibre and the recording electrode was derived. With another method, the decline of the peak-to-peak amplitude of SFAPs detected along a multi-electrode was obtained. With both experimental methods, in general peak-to-peak amplitudes of SFAPs decreased with increasing recording distances, as was found in model results with present volume conduction theory. However, this behaviour was not found in all experiments. The rate of decline of the peak-to-peak amplitudes with recording distance was always less than in models

Changes in time and frequency related aspects of motor unit action potentials during fatigue

During fatigue the shape of motor unit action potentials (MUAPs) change. Characteristics of the MUAPs described before concern several time related aspects. No attention has been given to the frequency spectrum changes of MUAPS. The median frequency of MUAPS has now been determined for motor units in the extensor digitorum longus muscle of the rat. Some examples of the changes are shown during a fatiguing stimulation pattern (250 s of 40 Hz stimulation during one third of each second). In general the median frequency tends to change more quickly than the time characteristics of the MUAPs. The results do not allow to draw yet conclusions about the time and frequency characteristics during fatigue for mechanically identified types of motor unit

Violet stimulated luminescence dating of quartz from Luochuan (Chinese loess plateau): Agreement with independent chronology up to ∼600 ka

Luminescence dating at the Luochuan loess type (China) section is at present limited to ∼0.1 Ma using quartz blue light stimulated luminescence (BLSL), but can be extended back in time to ∼0.5 Ma by resorting to the more developmental post-infrared infrared stimulated luminescence (post-IR IRSL) and thermally transferred OSL (TT-OSL) signals. Since both the latter are associated with systematic uncertainties due to the potential (a)-thermal instability of these signals, a search continues for alternative, and demonstrably stable luminescence signals that can cover the entire Quaternary timescale. Here we explore the violet stimulated luminescence (VSL) signal at the Luochuan section, which provides a continuous archive of homogenous sediment with favourable luminescence characteristics and a solid independent age framework. By testing several VSL protocols and their associated performance, we demonstrate that the Multi-Aliquot Additive-Dose (MAAD) protocol produces a VSL chronology at Luochuan which is in agreement with independent ages up to ∼0.6 Ma. For a more representative environmental dose rate of ∼2 Gy/ka (∼35% lower than at Luochuan), the documented range of MAAD-VSL sensitivity (200-1800 Gy) would correspond to the ability to date sediment up to ∼1 Ma back in time, offering a remarkable advance over existing methods.</p