Electrophysiological evidence of adult human skeletal muscle fibres with multiple endplates and polyneuronal innervation
Electromyographic (EMG) signals were recorded using intramuscular electrodes at six different sites in the brachioradialis muscles during voluntary isometric contractions in four subjects. The potential waveforms and discharge patterns of up to 12 simultaneously active motor units were identified fr...
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Published in | The Journal of physiology Vol. 544; no. 2; pp. 549 - 565 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
Oxford, UK
The Physiological Society
15.10.2002
Blackwell Publishing Ltd Blackwell Science Inc |
Subjects | |
Online Access | Get full text |
ISSN | 0022-3751 1469-7793 |
DOI | 10.1113/jphysiol.2002.023267 |
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Summary: | Electromyographic (EMG) signals were recorded using intramuscular electrodes at six different sites in the brachioradialis
muscles during voluntary isometric contractions in four subjects. The potential waveforms and discharge patterns of up to
12 simultaneously active motor units were identified from each signal using computer-aided decomposition. Out of a total of
301 motor unit potentials identified, 23 potentials exhibited behaviour consistent with having been generated by muscle fibres
that were innervated by two different motoneurons at widely separated endplates. These potentials discharged in association
with two different motor units, but were blocked or delayed whenever the two motor units discharged within a few milliseconds
of one another. The blocking was consistent with a collision or refractoriness when one motoneuron tried to excite the fibre
while it was already conducting an action potential initiated by the other motoneuron. The delays were consistent with decreased
conduction velocity associated with incomplete recovery of the fibre after a preceding action potential. From the temporal
separation between the discharges of the two motoneurons that resulted in blocking, the spatial separation between the endplates
was estimated to be between 26 and 44 mm. These findings challenge the classical concept of the motor unit as an anatomically
distinct and functionally independent entity. It is suggested that the human brachioradialis muscle may contain both long,
polyneuronally innervated fibres and short, serially linked, singly innervated fibres. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.2002.023267 |