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  • 1
    Electronic Resource
    Electronic Resource
    Development of Na inactivation in motor and sensory myelinated nerve fibres ofRana esculenta (1983)
    Springer
    Pflügers Archiv 398 (1983), S. 126-129 
    Details
    ISSN: 1432-2013
    Keywords: Myelinated nerve ; Motor fibre ; Sensory fibre ; Voltage clamp ; Na inactivation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Development of Na permeability inactivation was investigated in myelinated motor (N=12) and sensory (N=12) nerve fibres ofRana esculenta at 20° C. The K currents were blocked by 10 mM tetraethylammoniumchloride, added to the superfusing solution. Additionally, in 4 fibres of each group internal CsCl was applied by diffusion from the cut internodes. Development of Na inactivation was approximated by the sum of two exponentials. The time constants of the fast and slow inactivation phase (σh1 and σh2) were dependent on membrane potential (E) with similar values in both fibre types for a given E. In contrast, significant differences were found in the contribution of both phases. In motor nerve fibres the amplitude of the fast phase wasg=0.70 (mean value of 12 fibres) throughout the potential range investigated (−30 mV≤E≤40 mV). In sensory fibres g was potential dependent, increasing from 0.76 (mean value of 12 fibres) at E=−30 mV to unity at E〉30 mV. This difference in Na permeability inactivation is a further distinguishing property between motor and sensory nerve fibres.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00581059
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The effects of motor unit synchronization on the power spectrum of the electromyogram (1984)
    Springer
    Biological cybernetics 51 (1984), S. 71-77 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract A realistic model for two synchronized motor unit action potential trains (MUAPT) is presented in which the variability of the time difference between corresponding action potentials (hereafter denoted by delay) is taken into account. Specifically, this delay is modeled as a continuous random variable that may assume both positive and negative values. Expressions are derived for the auto- and cross-power spectra of two such trains using their relations with the auto- and cross-correlation functions, respectively, with which they form Fourier transform pairs. The results show that the auto- and the cross-power spectra of two such synchronized MUAPTs differ from the auto- and the cross-spectra of two independent MUAPTs. The contribution of the statistics of the interpulse intervals to one of the autopower spectra is smaller and the cross-power spectra no longer reduce to a Dirac δ-function at the origin but are now determined by the other auto-power spectrum and by the Fourier transform of the density function associated with the time difference between corresponding action potentials. As a consequence of this change in the cross-power spectra synchronization leads to an absolute increase of power at low frequencies and to a relative decrease of power at high frequencies. The results are then generalized to electromyograms (EMG) composed of more than just two MUAPTs and illustrated with simulated power spectra with which the theory shows excellent agreement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00357919
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Spectral analysis of the surface electromyogram as a tool for studying rate modulation: A comparison between theory, simulation, and experiment (1984)
    Springer
    Biological cybernetics 50 (1984), S. 95-103 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Theoretical work suggests that if the interpulse intervals (IPIs) of motor unit action potential trains (MUAPTs) are independently and normally distributed, then spectral analysis of the electromyogram could be a useful tool for studying rate modulation by virtue of the presence of a peak in the power spectrum at the average firing frequency of all active motor units. It is shown in this paper that IPIs need not be normally distributed, specifically that the results are very much the same if the IPIs are distributed according to a Gamma probability density function (PDF). Simulation of the electromyogram based on this theory proved the applicability of the method. Experimental results obtained for the masseter, biceps brachii and first dorsal interosseus (FDI) muscles, however, were in disagreement with both theory and simulation except for the biceps muscle at force levels up to 20% of the maximal force and for the masseter and FDI muscles in 1 out of 5 subjects. This indicates that the models for MUAPTs hitherto used might not be generally correct. Apart from this discrepancy, our results reveal differences between masseter and FDI muscles on the one hand and the biceps brachii on the other, which indicate that motor unit synchronisation is much more pronounced in the latter muscle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00337156
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    Paper (German National Licenses)
    Fulltext
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