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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 355 (1975), S. 291-306 
    ISSN: 1432-2013
    Keywords: Neuromuscular Transmission ; Isotonic Contraction ; Muscle Length ; Feedback
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effect of isotonic contraction on neuromuscular impulse transmission was studied in thein vivo M. gastrocnemius preparation of the frog. The N. ischiadicus was stimulated regularly with single pulses at different frequencies in the range of 1/8 to 8 Hz. When steady state conditions were reached, each half-minute a second stimulus was added to one of these pulses. The interval between the pulses of the pair was varied within the contraction cycle of the first stimulus. Compound extracellular or single intracellular action potentials were recorded from the muscle. At frequencies of 1/2–2 Hz a depression of the amplitude of the second compound muscle action potential of up to 50% of the first response was found when the muscle contracted isotonically. However, the second response was facilitated during an isometric contraction. The time course of the depression was equal to that of muscle shortening during the twitch, while the time course of facilitation corresponded roughly to that of facilitation of transmitter release. At lower frequencies the “isotonic depression” or “isometric facilitation” was not or only slightly present. However, at 1/8 Hz the depression could be evoked or increased by curarization. At frequencies higher than 2 Hz facilitation dominated over depression under isotonic conditions. With flexible intracellular micro-electrodes it was shown that the depression of the amplitude of the compound muscle action potential observed during the isotonic twitch was due to a reduction in neuromuscular impulse transmission. It is concluded that the isotonic depression is a negative feedback effect of the change of length of the contracting muscle on synaptic impulse transmission, probably due to an effect of length on transmitter release.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 155 (1978), S. 327-348 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: End-plate distributions have been determined for three frog muscles of different morphology in order to relate end-plate topography to spatial muscle structure and nerve branching. Koelle's cholinesterase technique was applied, both on whole muscles and frozen sections. The end-plates of the short parallel-fibered cutaneus pectoris muscle appeared to be located in short bands along the nerve branches. The nerve tree is restricted to a zonal area across the middle part of the muscle. Depending on the way the nerve branches, the end-plate bands form innervation patterns, varying from one single continuous band to multiple distributed bands. In the latter case one frequently observes that different end-plate bands do not run across the same longitudinal muscle fiber area, although the respective nerve branches run parallel across this area. The long parallel-fibered sartorius muscle has a wider nerve tree and exhibits the same phenomenon for close parallel nerve branches, but end-plate bands along parallel nerve branches far apart cover the same muscle fiber area. The end-plate distribution in the bipennate, short-fibered gastrocnemius is zonal throughout the muscle except in certain compartments containing tonic fibers. The end-plate zone centers around the inner aponeurosis about half-way between the muscle tendon junctions of the fibers and is visible only at the muscle surface where muscle fibers run over their entire length at that surface. The results are of general use in the electrophysiology of neuromuscular transmission because they illustrate how in certain twitch muscles neuromuscular morphology may help to localize end-plates.
    Type of Medium: Electronic Resource
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