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Increases in human motoneuron excitability after cervical spinal cord injury depend on the level of injury
Umeå University, Faculty of Medicine, Department of Community Medicine and Rehabilitation, Physiotherapy.
2017 (English)In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 117, no 2, 684-691 p.Article in journal (Refereed) Published
Abstract [en]

After human spinal cord injury (SCI), motoneuron recruitment and firing rate during voluntary and involuntary contractions may be altered by changes in motoneuron excitability. Our aim was to compare F-waves in single thenar motor units paralyzed by cervical SCI to those in uninjured controls because at the single unit level, F-waves primarily reflect the intrinsic properties of the motoneuron and its initial segment. With intraneural motor axon stimulation, F-waves were evident in all four participants with C4-level SCI, absent in eight with C5 or C6 injury, and present in six of 12 Uninjured participants (p<0.001). The percentage of units that generated F-waves differed across groups (C4: 30%; C5 or C6: 0%; Uninjured: 16%; p<0.001). Mean (± SD) proximal axon conduction velocity was slower after C4 SCI (64±4 m/s, n=6 units; Uninjured: 73±8 m/s, n=7 units, p=0.037). Mean distal axon conduction velocity differed by group (C4: 40±8 m/s, n=20 units; C5 or C6: 49±9 m/s, n=28; Uninjured: 60±7 m/s, n=45; p<0.001). Motor unit properties (EMG amplitude, twitch force) only differed after SCI, not by injury level (p≤0.004). Motor units with F-waves had distal conduction velocities, M-wave amplitudes, and twitch forces that spanned the respective group range, indicating that units with heterogeneous properties produced F-waves. Recording unitary F-waves has shown that thenar motoneurons closer to the SCI (C5 or C6) have reduced excitability, whereas those further away (C4) have increased excitability, which may exacerbate muscle spasms. This difference in motoneuron excitability may be related to the extent of membrane depolarization following SCI.

Place, publisher, year, edition, pages
2017. Vol. 117, no 2, 684-691 p.
Keyword [en]
F wave, proximal axon conduction velocity, single motor unit
National Category
Physiotherapy
Identifiers
URN: urn:nbn:se:umu:diva-130658DOI: 10.1152/jn.00676.2016ISI: 000393863600019PubMedID: 27852734OAI: oai:DiVA.org:umu-130658DiVA: diva2:1069184
Available from: 2017-01-27 Created: 2017-01-27 Last updated: 2017-04-21Bibliographically approved

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CiteExportLink to record
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  • apa
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