期刊
JOURNAL OF NEUROPHYSIOLOGY
卷 124, 期 1, 页码 63-85出版社
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/jn.00194.2020
关键词
high-density surface EMG; motoneurons; persistent inward currents; recruitment threshold; tibialis anterior
资金
- National Institute of Neurological Disorders and Stroke [R01 NS-104436]
- National Science and Engineering Grant [05205]
- Women and Children's Health Research Institute at the University of Alberta
- Neuroscience and Mental Health Institute at the University of Alberta
Persistent inward calcium and sodium currents (I-P) activated during motoneuron recruitment help synaptic inputs maintain self-sustained firing until derecruitment. Here, we estimate the contribution of the I-P to self-sustained firing in human motoneurons of varying recruitment threshold by measuring the difference in synaptic input needed to maintain minimal firing once the I-P is fully activated compared with the larger synaptic input required to initiate firing before full I-P activation. Synaptic input to approximate to 20 dorsiflexor motoneurons simultaneously recorded during ramp contractions was estimated from firing profiles of motor units decomposed from high-density surface electromyography (EMG). To avoid errors introduced when using high-threshold units firing in their nonlinear range, we developed methods where the lowest threshold units firing linearly with force were used to construct a composite (control) unit firing rate profile to estimate synaptic input to higher threshold (test) units. The difference in the composite firing rate (synaptic input) at the time of test unit recruitment and derecruitment (Delta F = F-recruit = F-derecruit) was used to measure I-P amplitude that sustained firing. Test units with recruitment thresholds 1-30% of maximum had similar Delta F values, which likely included both slow and fast motor units activated by small and large motoneurons, respectively. This suggests that the portion of the I-P that sustains firing is similar across a wide range of motoneuron sizes. NEW & NOTEWORTHY A new method of estimating synaptic drive to multiple, simultaneously recorded motor units provides evidence that the portion of the depolarizing drive from persistent inward currents that contributes to self-sustained firing is similar across motoneurons of different sizes.
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