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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 45 (1982), S. 417-427 
    ISSN: 1432-1106
    Keywords: Primary muscle spindle endings ; Motor units ; Tremor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Discharge patterns of group Ia afferents of muscle spindles in the (isometric) cat semitendinosus muscle were recorded when subjected to the influence of contractions of three motor units elicited by stimulation of three α-efferents with different regular or stochastic stimulus patterns. In order to study conditioning interactions between motor unit contractions, defined time constellations of stimuli to different motor units were isolated from the stimulus trains by electronic means. This technique was also applied to discharge patterns of two Ia fibres to isolate “correlated discharges”. The effects of defined time constellations of stimuli upon discharge patterns of single Ia afferents or “correlated discharges” of pairs of Ia afferents were assessed by poststimulus time histograms (PSTHs). It turned out that the influence exerted by one motor unit on spindle discharges was more or less strongly modulated by actions of the other motor units, dependent on the relative timing of their contractions. These effects could in part be explained by the relative locations of motor units and spindles within the muscle. These results are discussed with respect to possible mechanisms of low-amplitude physiological tremor.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2013
    Keywords: Primary muscle spindle endings ; Discharge statistics ; Isometric muscle contraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A feature frequently observed in interspike interval histograms (IH) derived from stationary Ia fibre discharge patterns was a bimodality suggesting a mixed population composed of two sub-populations of possibly different origins. To verify this hypothesis a separation of these subpopulations was attempted by assuming a Gaussian distribution for the longer intervals. The success of such a separation depended on the distinctness of the histogram peaks and the relative sizes of each mode. Both factors in turn depended on the overall muscle length and, hence, on the mean spindle discharge rate. The smaller intervals were then isolated from the spike trains and submitted to further statistical analysis. By averaging overall muscle tension with respect to the smaller intervals, the latter could often be linked to tension trajectories which were of higher amplitude and faster time course than the trajectories obtained by averaging with respect to the rest of the spikes. In some cases, autocorrelation histograms of isolated small intervals as well as serial correlograms computed for all intervals indicated that some muscle spindle afferents responded sensitively to activity of single motor units. This would confirm recent results of Cameron et al. (1980).
    Type of Medium: Electronic Resource
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