Electrophysiological evidence of adult human skeletal muscle fibres with multiple endplates and polyneuronal innervation.

Full Abstract

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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Author information

Author/s: Lateva, Zoia C (ZC); McGill, Kevin C (KC); Johanson, M Elise (ME);

Affiliation: Rehabilitation Research and Development Center, Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94304, USA. leteva@rrdmail.stanford.edu

Journal and publication information

Publication Type: Journal Article; Research Support, U.S. Gov't, Non-P.H.S.

Journal: The Journal of physiology (J Physiol), published in England. (Language: eng)

Reference: 2002-Oct; vol 544 (issue Pt 2) : pp 549-65

Dates: Created 2002/10/16; Completed 2003/04/15; Revised 2006/11/15;

PMID: 12381826, status: MEDLINE (last retrieval date: 11/6/2008)

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Motor Endplate - physiology
Motor Neurons - physiology
Muscle Fibers
Muscle, Skeletal - innervation; physiology
Neural Conduction
Neural Inhibition
Reaction Time
Refractory Period, Electrophysiological
Time Factors

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