Cargando…
Motor unit firing rates during spasms in thenar muscles of spinal cord injured subjects
Involuntary contractions of paralyzed muscles (spasms) commonly disrupt daily activities and rehabilitation after human spinal cord injury (SCI). Our aim was to examine the recruitment, firing rate modulation, and derecruitment of motor units that underlie spasms of thenar muscles after cervical SCI...
Autores principales: | , , |
---|---|
Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
Frontiers Media S.A.
2014
|
Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4231945/ https://www.ncbi.nlm.nih.gov/pubmed/25452723 http://dx.doi.org/10.3389/fnhum.2014.00922 |
_version_ | 1782344505293275136 |
---|---|
author | Zijdewind, Inge Bakels, Rob Thomas, Christine K. |
author_facet | Zijdewind, Inge Bakels, Rob Thomas, Christine K. |
author_sort | Zijdewind, Inge |
collection | PubMed |
description | Involuntary contractions of paralyzed muscles (spasms) commonly disrupt daily activities and rehabilitation after human spinal cord injury (SCI). Our aim was to examine the recruitment, firing rate modulation, and derecruitment of motor units that underlie spasms of thenar muscles after cervical SCI. Intramuscular electromyographic activity (EMG), surface EMG, and force were recorded during thenar muscle spasms that occurred spontaneously or that were triggered by movement of a shoulder or leg. Most spasms were submaximal (mean: 39%, SD: 33 of the force evoked by median nerve stimulation at 50 Hz) with strong relationships between EMG and force (R(2) > 0.69). Unit recruitment occurred over a wide force range (0.2–103% of 50 Hz force). Significant unit rate modulation occurred during spasms (frequency at 25% maximal force: 8.8 Hz, 3.3 SD; at maximal force: 16.1 Hz, 4.1 SD). Mean recruitment frequency (7.1 Hz, 3.2 SD) was significantly higher than derecruitment frequency (5.4 Hz, 2.4 SD). Coactive unit pairs that fired for more than 4 s showed high (R(2) > 0.7, n = 4) or low (R(2):0.3–0.7, n = 12) rate-rate correlations, and derecruitment reversals (21 pairs, 29%). Later recruited units had higher or lower maximal firing rates than lower threshold units. These discrepant data show that coactive motoneurons are drive both by common inputs and by synaptic inputs from different sources during muscle spasms. Further, thenar motoneurons can still fire at high rates in response to various peripheral inputs after SCI, supporting the idea that low maximal voluntary firing rates and forces in thenar muscles result from reduced descending drive. |
format | Online Article Text |
id | pubmed-4231945 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2014 |
publisher | Frontiers Media S.A. |
record_format | MEDLINE/PubMed |
spelling | pubmed-42319452014-12-01 Motor unit firing rates during spasms in thenar muscles of spinal cord injured subjects Zijdewind, Inge Bakels, Rob Thomas, Christine K. Front Hum Neurosci Neuroscience Involuntary contractions of paralyzed muscles (spasms) commonly disrupt daily activities and rehabilitation after human spinal cord injury (SCI). Our aim was to examine the recruitment, firing rate modulation, and derecruitment of motor units that underlie spasms of thenar muscles after cervical SCI. Intramuscular electromyographic activity (EMG), surface EMG, and force were recorded during thenar muscle spasms that occurred spontaneously or that were triggered by movement of a shoulder or leg. Most spasms were submaximal (mean: 39%, SD: 33 of the force evoked by median nerve stimulation at 50 Hz) with strong relationships between EMG and force (R(2) > 0.69). Unit recruitment occurred over a wide force range (0.2–103% of 50 Hz force). Significant unit rate modulation occurred during spasms (frequency at 25% maximal force: 8.8 Hz, 3.3 SD; at maximal force: 16.1 Hz, 4.1 SD). Mean recruitment frequency (7.1 Hz, 3.2 SD) was significantly higher than derecruitment frequency (5.4 Hz, 2.4 SD). Coactive unit pairs that fired for more than 4 s showed high (R(2) > 0.7, n = 4) or low (R(2):0.3–0.7, n = 12) rate-rate correlations, and derecruitment reversals (21 pairs, 29%). Later recruited units had higher or lower maximal firing rates than lower threshold units. These discrepant data show that coactive motoneurons are drive both by common inputs and by synaptic inputs from different sources during muscle spasms. Further, thenar motoneurons can still fire at high rates in response to various peripheral inputs after SCI, supporting the idea that low maximal voluntary firing rates and forces in thenar muscles result from reduced descending drive. Frontiers Media S.A. 2014-11-14 /pmc/articles/PMC4231945/ /pubmed/25452723 http://dx.doi.org/10.3389/fnhum.2014.00922 Text en Copyright © 2014 Zijdewind, Bakels and Thomas. http://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution and reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. |
spellingShingle | Neuroscience Zijdewind, Inge Bakels, Rob Thomas, Christine K. Motor unit firing rates during spasms in thenar muscles of spinal cord injured subjects |
title | Motor unit firing rates during spasms in thenar muscles of spinal cord injured subjects |
title_full | Motor unit firing rates during spasms in thenar muscles of spinal cord injured subjects |
title_fullStr | Motor unit firing rates during spasms in thenar muscles of spinal cord injured subjects |
title_full_unstemmed | Motor unit firing rates during spasms in thenar muscles of spinal cord injured subjects |
title_short | Motor unit firing rates during spasms in thenar muscles of spinal cord injured subjects |
title_sort | motor unit firing rates during spasms in thenar muscles of spinal cord injured subjects |
topic | Neuroscience |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4231945/ https://www.ncbi.nlm.nih.gov/pubmed/25452723 http://dx.doi.org/10.3389/fnhum.2014.00922 |
work_keys_str_mv | AT zijdewindinge motorunitfiringratesduringspasmsinthenarmusclesofspinalcordinjuredsubjects AT bakelsrob motorunitfiringratesduringspasmsinthenarmusclesofspinalcordinjuredsubjects AT thomaschristinek motorunitfiringratesduringspasmsinthenarmusclesofspinalcordinjuredsubjects |