Persistent inward currents in motoneuron dendrites: Implications for motor output
Bibliographic record
Abstract
The dendrites of motoneurons are not, as once thought, passive conduits for synaptic inputs. Instead they have voltage-dependent channels that provide the capacity to generate a very strong persistent inward current (PIC). The amplitude of the PIC is proportional to the level of neuromodulatory input from the brainstem, which is mediated primarily by the monoamines serotonin and norepinephrine. During normal motor behavior, monoaminergic drive is likely to be moderately strong and the dendritic PIC generates many of the characteristic features of motor unit firing patterns. Most of the PIC activates at or below recruitment threshold and thus motor unit firing patterns exhibit a linear increase just above recruitment. The dendritic PIC allows motor unit derecruitment to occur at a lower input level than recruitment, thus providing sustained tonic firing with little or no synaptic input, especially in low-threshold units. However the dendritic PIC can be readily deactivated by synaptic inhibition. The overall amplification due to the dendritic PIC and other effects of monoamines on motoneurons greatly increases the input-output gain of the motor pool. Thus the brainstem neuromodulatory input provides a mechanism by which the excitability of motoneurons can be varied for different motor behaviors. This control system is lost in spinal cord injury but PICs nonetheless recover near-normal amplitudes in the months following the initial injury. The relationship of these findings to the cause of the spasticity syndrome developing after spinal cord injury is discussed.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.003 |
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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".