Intrinsic Activation of Human Motoneurons: Possible Contribution to Motor Unit Excitation
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Bibliographic record
Abstract
The main purpose of this study was to estimate the contribution of intrinsic activation of human motoneurons (e.g., by plateau potentials) during voluntary and reflexive muscle contractions. Pairs of motor units were recorded from either the tibialis anterior or soleus muscle during three different conditions: 1) during a brief muscle vibration followed by a slow relaxation of a steady isometric contraction; 2) during a triangular isometric torque contraction; and 3) during passive sinusoidal muscle stretch superimposed on a steady isometric contraction. In each case, the firing rate of a tonically firing control motor unit was used as a measure of the effective synaptic excitation (i.e., synaptic drive) to a slightly higher-threshold test motor unit that was recruited and de-recruited during a contraction trial. The firing rate of the control unit was compared at recruitment and de-recruitment of the test unit. This was done to determine whether the estimated synaptic drive needed to recruit a motor unit was less than the amount needed to sustain firing as a result of an added depolarization produced from intrinsic sources. After test unit recruitment, the firing rate of the control unit could be decreased significantly (on average by 3.6 Hz from an initial recruitment rate of 9.8 Hz) before the test unit was de-recruited during a descending synaptic drive. Similar decreases in control unit rate occurred in all three experimental conditions. This represents a possible 40% reduction in the estimated synaptic drive needed to maintain firing of a motor unit compared with the estimated amount needed to recruit the unit initially. The firing rates of both the control and test units were modulated together in a highly parallel fashion, suggesting that the unit pairs were driven by common synaptic inputs. This tight correlation further validated the use of the control unit firing rate as a monitor of synaptic drive to the test motor unit. The estimates of intrinsically mediated depolarization of human motoneurons ( approximately 40% during moderate contractions) are consistent with values obtained for plateau potentials obtained from intracellular recordings of motoneurons in reduced animal preparations, although various alternative mechanisms are discussed. This suggests that similar intrinsic conductances provide a substantial activation of human motoneurons during moderate physiological activity.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it