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

Abstract

In vivo records of single fibre action potentials (SFAPs) have always been obtained at unknown distance from the active muscle fibre. 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. 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 microns recording distance is not as dominant for the SFAP shape as expected. 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.

Detection of motor unit action potentials with surface electrodes: influence of electrode size and spacing

“…2A, B). When the electrode was at the fiber perimeter, the duration of the simulated action potential (250 laS) was somewhat larger than that observed experimentally (60 170~ts, Albers et al 1989;Ekstedt 1964;Gath and St&lberg 1975). In the model, peak-to-peak duration depended on conduction velocity and dipole spacing when the electrode was near the fiber.…”

“…2B). Albers et al (1989), using an elegant method, recorded muscle fiber action potentials of 2.4-3.2 mV at an electrode-fiber distance of about 1001am, and 0.7-0.9mV at 300pm. Similar values were seen in the present study; simulated muscle fiber action potentials at distances of 100 ~tm and 300 Ixm had peak-to-peak amplitudes of 3.3 and 0.7 mV, respectively.…”

Electromyography (EMG) Modeling

“…In such cases, the SFP at short fiber-electrode distances decreases (instead of increasing) because the fiber-electrode distance becomes larger in the equivalent volume conductor. Thus, the results obtained by the two ways are not identical, which can be a reason the SFP simulated at short fiber-electrode distances to be of lower amplitude than the measured ones (34,35,37,40).…”

“…Another way is to increase all radial and transversal dimensions of the volume conductor (9,(34)(35)(36)(37)(38)(39)(40) and of the fiber diameter HK an -times (32). The increase in fiber diameter is often not considered in simulation studies.…”

Analysis of the relationship between the rise-time and the amplitude of single-fibre potentials in human muscles

“…Since the introduction of the D-D and N-S convolutional models, few studies have addressed the accuracy of the underlying SFAP approximations (Albers et al, 1989;Van Veen et al, 1993;Rodriguez et al, 2006). The accuracy of SFAP models is predominantly related to their ability to generate potentials as similar as possible to experimental recordings.…”