Articles de revues : « Firing unit »

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Contessa, Paola, Alexander Adam et Carlo J. De Luca. « Motor unit control and force fluctuation during fatigue ». Journal of Applied Physiology 107, n^o 1 (juillet 2009) : 235–43. http://dx.doi.org/10.1152/japplphysiol.00035.2009.

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During isometric contractions, the fluctuation of the force output of muscles increases as the muscle fatigues, and the contraction is sustained to exhaustion. We analyzed motor unit firing data from the vastus lateralis muscle to investigate which motor unit control parameters were associated with the increased force fluctuation. Subjects performed a sequence of isometric constant-force contractions sustained at 20% maximal force, each spaced by a 6-s rest period. The contractions were performed until the mean value of the force output could not be maintained at the desired level. Intramuscular EMG signals were detected with a quadrifilar fine-wire sensor. The EMG signals were decomposed to identify all of the firings of several motor units by using an artificial intelligence-based set of algorithms. We were able to follow the behavior of the same motor units as the endurance time progressed. The force output of the muscle was filtered to remove contributions from the tracking task. The coefficient of variation of the force was found to increase with endurance time ( P < 0.001, R2 = 0.51). We calculated the coefficient of variation of the firing rates, the synchronization of pairs of motor unit firings, the cross-correlation value of the firing rates of pairs of motor units, the cross-correlation of the firing rates of motor units and the force, and the number of motor units recruited during the contractions. Of these parameters, only the cross-correlation of the firing rates ( P < 0.01, R2 = 0.10) and the number of recruited motor units ( P = 0.042, R2 = 0.22) increased significantly with endurance time for grouped subjects. A significant increase ( P < 0.001, R2 = 0.16) in the cross-correlation of the firing rates and force was also observed. It is suggested that the increase in the cross-correlation of the firing rates is likely due to a decrease in the sensitivity of the proprioceptive feedback from the spindles.

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Contessa, Paola, Carlo J. De Luca et Joshua C. Kline. « The compensatory interaction between motor unit firing behavior and muscle force during fatigue ». Journal of Neurophysiology 116, n^o 4 (1 octobre 2016) : 1579–85. http://dx.doi.org/10.1152/jn.00347.2016.

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Throughout the literature, different observations of motor unit firing behavior during muscle fatigue have been reported and explained with varieties of conjectures. The disagreement amongst previous studies has resulted, in part, from the limited number of available motor units and from the misleading practice of grouping motor unit data across different subjects, contractions, and force levels. To establish a more clear understanding of motor unit control during fatigue, we investigated the firing behavior of motor units from the vastus lateralis muscle of individual subjects during a fatigue protocol of repeated voluntary constant force isometric contractions. Surface electromyographic decomposition technology provided the firings of 1,890 motor unit firing trains. These data revealed that to sustain the contraction force as the muscle fatigued, the following occurred: 1) motor unit firing rates increased; 2) new motor units were recruited; and 3) motor unit recruitment thresholds decreased. Although the degree of these adaptations was subject specific, the behavior was consistent in all subjects. When we compared our empirical observations with those obtained from simulation, we found that the fatigue-induced changes in motor unit firing behavior can be explained by increasing excitation to the motoneuron pool that compensates for the fatigue-induced decrease in muscle force twitch reported in empirical studies. Yet, the fundamental motor unit control scheme remains invariant throughout the development of fatigue. These findings indicate that the central nervous system regulates motor unit firing behavior by adjusting the operating point of the excitation to the motoneuron pool to sustain the contraction force as the muscle fatigues.

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Sauvage, Chloe, Mario Manto, Alexander Adam, Rick Roark, Patrice Jissendi et Carlo J. De Luca. « Ordered Motor-Unit Firing Behavior in Acute Cerebellar Stroke ». Journal of Neurophysiology 96, n^o 5 (novembre 2006) : 2769–74. http://dx.doi.org/10.1152/jn.00268.2006.

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It is known that at any given force level, the lower-threshold motor units generally fire at greater rates than the higher-threshold units during isometric tasks of extremity muscles. In addition to this hierarchical arrangement, firing rates of motor units fluctuate in unison with nearly no time delay; an observation that has led to the concept of common drive, a basic motoneuronal rule. Although it is established that the cerebellum plays a critical function in motor control, its role in the genesis, triggering, selection, and monitoring of motor-unit firing pattern discharges during isometric tasks is unknown. We applied an electromyographic (EMG) decomposition technique, known as precision decomposition, to accurately identify motor-unit firing times from the EMG signal recorded from the first dorsal interosseous muscle to unravel the features of motor-unit firings in three patients presenting a unilateral cerebellar stroke and exhibiting an acute cerebellar syndrome. We observed ataxic isometric force during visually guided abduction of the index finger on the affected side. However, the hierarchical response of individual motor units was spared. Furthermore, acute cerebellar ataxia was not associated with a loss of the common drive.

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Eggermont, Jos J., et Jennifer E. Mossop. « Azimuth Coding in Primary Auditory Cortex of the Cat. I. Spike Synchrony Versus Spike Count Representations ». Journal of Neurophysiology 80, n^o 4 (1 octobre 1998) : 2133–50. http://dx.doi.org/10.1152/jn.1998.80.4.2133.

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Eggermont, Jos J. and Jennifer E. Mossop. Azimuth coding in primary auditory cortex of the cat. I. Spike synchrony versus spike count representations. J. Neurophysiol. 80: 2133–2150, 1998. The neural representation of sound azimuth in auditory cortex most often is considered to be average firing rate, and azimuth tuning curves based thereupon appear to be rather broad. Coincident firings of simultaneously recorded neurons could provide an improved representation of sound azimuth compared with that contained in the firing rate in either of the units. In the present study, a comparison was made between local field potentials and several measures based on unit firing rate and coincident firing with respect to their azimuth-tuning curve bandwidth. Noise bursts, covering a 60-dB intensity range, were presented from nine speakers arranged in a semicircular array with a radius of 55 cm in the animal's frontal half field. At threshold intensities, all local field potential (LFP) recordings showed preferences for contralateral azimuths. Multiunit recordings showed in 74% a threshold for contralateral azimuths, in 16% for frontal azimuths, and in only 5% showed an ipsilateral threshold. The remaining 5% were not spatially tuned. Representations for directionally sensitive units based on coincident firings provided significantly sharper tuning (50–60° bandwidth at 25 dB above the lowest threshold) than those based on firing rate (bandwidths of 80–90°). The ability to predict sound azimuth from the directional information contained in the neural population activity was simulated by combining the responses of the 102 single units. Peak firing rates and coincident firings with LFPs at the preferred azimuth for each unit were used to construct a population vector. At stimulus levels of ≥40 dB SPL, the prediction function was sigmoidal with the predicted frontal azimuth coinciding with the frontal speaker position. Sound azimuths >45° from the midline all resulted in predicted values of −90 or 90°, respectively. No differences were observed in the performance of the prediction based on firing rate or coincident firings for these intensities. This suggests that although coincident firings produce narrower azimuth tuning curves, the information contained in the overall neural population does not increase compared with that contained in a firing rate representation. The relatively poor performance of the population vector further suggests that primary auditory cortex does not code sound azimuth by a globally distributed measure of peak firing rate or coincident firing.

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Deburchgraeve, W., K. Van Damme, T. Adriaensen, A. Spaepen, S. Van Huffel et J. Taelman. « Detection Algorithm for Single Motor Unit Firing in Surface EMG of the Trapezius Muscle ». Methods of Information in Medicine 49, n^o 05 (2010) : 492–95. http://dx.doi.org/10.3414/me09-02-0042.

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Summary Background: Work-related musculoskeletal disorders (MSD) of the neck and the shoulders are a growing problem in society. An interesting pattern of spontaneous muscle activity, the firing of a single motor unit, in the trapezius muscle is observed during a laboratory study in a rest state or a state with a mental load. Objective: In this study, we report on the finding of the single motor unit firing and we present a detection algorithm to localize these single motor unit firings. Methods: A spike train detection algorithm, using a nonlinear energy operator and correlation, is presented to detect burst of highly correlated, high energetic spike-like segments. Results: This single motor unit was visible in 65% of the test subjects on one or both trapezius muscles although there was no change in posture of the test subjects. All the segments in the data that were determined as single motor unit firings were detected by the algorithm. Discussion: The physiological meaning of this firing pattern is a very low and subconscious contraction of the muscle. A long-term contraction could lead to the exhaustion of the muscle fibers, thus resulting in musculoskeletal disorders. The detection algorithm is able to localize this phenomenon in a sEMG measurement. The ability of detecting these firings is helpful in the research of its origin. Conclusion: The detection algorithm can be used to gain insight in the physiological origin of this phenomenon. In addition, the algorithm can also be used in a biofeedback system to warn the user for this undesired contraction to prevent MSD.

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Adam, Alexander, Carlo J. De Luca et Zeynep Erim. « Hand Dominance and Motor Unit Firing Behavior ». Journal of Neurophysiology 80, n^o 3 (1 septembre 1998) : 1373–82. http://dx.doi.org/10.1152/jn.1998.80.3.1373.

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Adam, Alexander, Carlo J. De Luca, and Zeynep Erim. Hand dominance and motor unit firing behavior. J. Neurophysiol. 80: 1373–1382, 1998. Daily preferential use was shown to alter physiological and mechanical properties of skeletal muscle. This study was aimed at revealing differences in the control strategy of muscle pairs in humans who show a clear preference for one hand. We compared the motor unit (MU) recruitment and firing behavior in the first dorsal interosseous (FDI) muscle of both hands in eight male volunteers whose hand preference was evaluated with the use of a standard questionnaire. Myoelectric signals were recorded while subjects isometrically abducted the index finger at 30% of the maximal voluntary contraction (MVC) force. A myoelectric signal decomposition technique was used to accurately identify MU firing times from the myoelectric signal. In MUs of the dominant hand, mean values for recruitment threshold, initial firing rate, average firing rate at target force, and discharge variability were lower when compared with the nondominant hand. Analysis of the cross-correlation between mean firing rate and muscle force revealed cross-correlation peaks of longer latency in the dominant hand than in the nondominant side. This lag of the force output with respect to fluctuations in the firing behavior of MUs is indicative of a greater mechanical delay in the dominant FDI muscle. MVC force was not significantly different across muscle pairs, but the variability of force at the submaximal target level was higher in the nondominant side. The presence of lower average firing rates, lower recruitment thresholds, and greater firing rate/force delay in the dominant hand is consistent with the notion of an increased percentage of slow twitch fibers in the preferentially used muscle, allowing twitch fusion and force buildup to occur at lower firing rates. It is suggested that a lifetime of preferred use may cause adaptations in the fiber composition of the dominant muscle such that the mechanical effectiveness of its MUs increased.

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Bennett, David J., Yunru Li, Philip J. Harvey et Monica Gorassini. « Evidence for Plateau Potentials in Tail Motoneurons of Awake Chronic Spinal Rats With Spasticity ». Journal of Neurophysiology 86, n^o 4 (1 octobre 2001) : 1972–82. http://dx.doi.org/10.1152/jn.2001.86.4.1972.

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Motor units of segmental tail muscles were recorded in awake rats following acute (1–2 days) and chronic (>30 days) sacral spinal cord transection to determine whether plateau potentials contributed to sustained motor-unit discharges after injury. This study was motivated by a companion in vitro study that indicated that after chronic spinal cord injury, the tail motoneurons of the sacrocaudal spinal cord exhibit persistent inward currents ( I PIC) that cause intrinsically sustained depolarizations ( plateau potentials) and firing ( self-sustained firing). Importantly, in this companion study, the plateaus were fully activated at recruitment and subsequently helped sustain the firing without causing abrupt nonlinearities in firing. That is, after recruitment and plateau activation, the firing rate was modulated relatively linearly with injected current and therefore provided a good approximation of the input to the motoneuron despite the plateau. Thus in the present study, pairs of motor units were recorded simultaneously from the same muscle, and the firing rate ( F) of the lowest-threshold unit (control unit) was used as an estimate of the synaptic input to both units. We then examined whether firing of the higher-threshold unit (test unit) was intrinsically maintained by a plateau, by determining whether more synaptic input was required to recruit the test unit than to maintain its firing. The difference in the estimated synaptic input at recruitment and de-recruitment of the test unit (i.e., change in control unit rate, Δ F) was taken as an estimate of the plateau current ( I PIC) that intrinsically sustained the firing. Slowly graded manual skin stimulation was used to recruit and then de-recruit the units. The test unit was recruited when the control unit rate was on average 17.8 and 18.9 Hz in acute and chronic spinal rats, respectively. In chronic spinal rats, the test unit was de-recruited when the control unit rate (re: estimated synaptic input) was significantly reduced, compared with at recruitment (Δ F = −5.5 Hz), and thus a plateau participated in maintaining the firing. In the lowest-threshold motor units, even a brief stimulation triggered very long-lasting firing (seconds to hours; self-sustained firing). Higher-threshold units required continuous stimulation (or a spontaneous spasm) to cause firing, but again more synaptic input was needed to recruit the unit than to maintain its firing (i.e., plateau present). In contrast, in acute spinal rats, the stimulation did not usually trigger sustained motor-unit firing that could be attributed to plateaus because Δ F was not significantly different from zero. These results indicate that plateaus play an important role in sustaining motor-unit firing in awake chronic spinal rats and thus contribute to the hyperreflexia and hypertonus associated with chronic injury.

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Masakado, Yoshihisa. « Motor Unit Firing Behavior in Man. » Keio Journal of Medicine 43, n^o 3 (1994) : 137–42. http://dx.doi.org/10.2302/kjm.43.137.

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Mettler, Joni A., et Lisa Griffin. « Motor Unit Firing Patterns during Fatigue ». Medicine & ; Science in Sports & ; Exercise 39, Supplement (mai 2007) : S330. http://dx.doi.org/10.1249/01.mss.0000274284.63883.9d.

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Kline, Joshua C., et Carlo J. De Luca. « Synchronization of motor unit firings : an epiphenomenon of firing rate characteristics not common inputs ». Journal of Neurophysiology 115, n^o 1 (1 janvier 2016) : 178–92. http://dx.doi.org/10.1152/jn.00452.2015.

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Synchronous motor unit firing instances have been attributed to anatomical inputs shared by motoneurons. Yet, there is a lack of empirical evidence confirming the notion that common inputs elicit synchronization under voluntary conditions. We tested this notion by measuring synchronization between motor unit action potential trains (MUAPTs) as their firing rates progressed within a contraction from a relatively low force level to a higher one. On average, the degree of synchronization decreased as the force increased. The common input notion provides no empirically supported explanation for the observed synchronization behavior. Therefore, we investigated a more probable explanation for synchronization. Our data set of 17,546 paired MUAPTs revealed that the degree of synchronization varies as a function of two characteristics of the motor unit firing rate: the similarity and the slope as a function of force. Both are measures of the excitation of the motoneurons. As the force generated by the muscle increases, the firing rate slope decreases, and the synchronization correspondingly decreases. Different muscles have motor units with different firing rate characteristics and display different amounts of synchronization. Although this association is not proof of causality, it consistently explains our observations and strongly suggests further investigation. So viewed, synchronization is likely an epiphenomenon, subject to countless unknown neural interactions. As such, synchronous firing instances may not be the product of a specific design and may not serve a specific physiological purpose. Our explanation for synchronization has the advantage of being supported by empirical evidence, whereas the common input does not.

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de Luca, C. J., P. J. Foley et Z. Erim. « Motor unit control properties in constant-force isometric contractions ». Journal of Neurophysiology 76, n^o 3 (1 septembre 1996) : 1503–16. http://dx.doi.org/10.1152/jn.1996.76.3.1503.

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1. The purpose of this study was 1) to characterize the decrease observed in mean firing rates of motor units in the first 8-15 s of isometric constant-force contractions and 2) to investigate possible mechanisms that could account for the ability to maintain force output in the presence of decreasing motor unit firing rates. 2. The decrease in mean firing rates was characterized by investigating myoelectric signals detected with a specialized quadrifilar needle electrode from the first dorsal interosseus (FDI) and the tibialis anterior (TA) muscles of 19 healthy subjects during a total of 85 constant-force isometric contractions at 30, 50, or 80% of maximal effort. The firing times of motor units were obtained from the myoelectric signals with the use of computer algorithms to decompose the signal into the constituent motor unit action potentials. Time-varying mean firing rates and recruitment thresholds were also calculated. 3. Motor units detected from the TA muscle were found to have a continual decrease in their mean firing rates in 36 of 44 trials performed during isometric ankle dorsiflexion at force values ranging from 30 to 80% of maximal effort and a duration of 8-15 s. Likewise, motor units detected in the FDI muscle displayed a decrease in firing rate in 32 of 41 trials performed during constant-force isometric index finger abduction for contractions ranging from 30 to 80% of maximal effort. In 14 contractions (16% of total), firing rates were essentially constant, whereas in 3 contractions (4%), firing rates appeared to increase. 4. Motor units with the higher recruitment thresholds and lower firing rates tended to display the greater decreases in firing rate over the constant-force interval, whereas motor units with lower recruitment thresholds and higher firing rates had lesser rates of decrease. Furthermore, increasing contraction levels tended to intensify the decrease in the motor unit firing rates. 5. Three possible mechanisms were considered as factors responsible for the maintaining of force output while motor units decreased their firing rates: motor unit recruitment, agonist/antagonist interaction, and twitch potentiation. Of these, motor unit recruitment was discarded first because none was observed during the 8-15 s duration of any of the 85 contractions. Furthermore, contractions outside the physiological range of motor unit recruitment (at 80% of maximal effort) revealed the same decreasing trend in firing rates, ruling out recruitment as the means of sustaining force output. 6. The role of agonist or antagonist muscle interaction was investigated with the use of the muscles controlling the wrist joint. Myoelectric signals were recorded with quadrifilar needle electrodes from the wrist extensor muscles while myoelectric activity in the wrist flexor muscles was concurrently monitored with surface electrodes during constant-force isometric wrist extension at 50% of maximal effort. Firing rates of the motor units in the wrist extensor muscles simultaneously decreased while the flexor muscles were determined to be inactive. 7. All the findings of this study regarding the behavior of the firing rates could be well explained by the reported characteristics of twitch potentiation that have been previously documented in animals and humans. 8. The results of this study, combined with the results of other investigators, provide the following scenario to explain how a constant-force isometric contraction is sustained. As the contraction progresses, the twitch force of the muscle fibers undergoes a potentiation followed by a decrease. Simultaneously, the "late adaptation" property of the motoneuron decreases the firing rate of the motor unit. Findings of this study suggest that voluntary reduction in firing rates also cannot be ruled out as a means to augment the adaptation in motoneurons. (ABSTRACT TRUNCATED)

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Mottram, C. J., C. J. Heckman, R. K. Powers, W. Z. Rymer et N. L. Suresh. « Disturbances of motor unit rate modulation are prevalent in muscles of spastic-paretic stroke survivors ». Journal of Neurophysiology 111, n^o 10 (15 mai 2014) : 2017–28. http://dx.doi.org/10.1152/jn.00389.2013.

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Stroke survivors often exhibit abnormally low motor unit firing rates during voluntary muscle activation. Our purpose was to assess the prevalence of saturation in motor unit firing rates in the spastic-paretic biceps brachii muscle of stroke survivors. To achieve this objective, we recorded the incidence and duration of impaired lower- and higher-threshold motor unit firing rate modulation in spastic-paretic, contralateral, and healthy control muscle during increases in isometric force generated by the elbow flexor muscles. Impaired firing was considered to have occurred when firing rate became constant (i.e., saturated), despite increasing force. The duration of impaired firing rate modulation in the lower-threshold unit was longer for spastic-paretic (3.9 ± 2.2 s) than for contralateral (1.4 ± 0.9 s; P < 0.001) and control (1.1 ± 1.0 s; P = 0.005) muscles. The duration of impaired firing rate modulation in the higher-threshold unit was also longer for the spastic-paretic (1.7 ± 1.6 s) than contralateral (0.3 ± 0.3 s; P = 0.007) and control (0.1 ± 0.2 s; P = 0.009) muscles. This impaired firing rate of the lower-threshold unit arose, despite an increase in the overall descending command, as shown by the recruitment of the higher-threshold unit during the time that the lower-threshold unit was saturating, and by the continuous increase in averages of the rectified EMG of the biceps brachii muscle throughout the rising phase of the contraction. These results suggest that impairments in firing rate modulation are prevalent in motor units of spastic-paretic muscle, even when the overall descending command to the muscle is increasing.

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Erim, Zeynep, M. Faisal Beg, David T. Burke et Carlo J. de Luca. « Effects of Aging on Motor-Unit Control Properties ». Journal of Neurophysiology 82, n^o 5 (1 novembre 1999) : 2081–91. http://dx.doi.org/10.1152/jn.1999.82.5.2081.

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It was hypothesized that the age-related alterations in the morphological properties of a motor unit would be accompanied by modifications in the control aspects of the motor unit, as either an adaptive or compensatory mechanism to preserve smooth force production. In specific, the objective of the study was to investigate the age-related alterations in the concurrent firing behavior of multiple motor units in the first dorsal interosseous (FDI) muscle in isometric contractions at 20 and 50% of the subject's voluntary contraction level. Analysis of the data collected from 10 young (24–37 yr of age) and 10 elderly (65–88 yr of age) subjects led to three novel observations regarding the firing behavior of aged motor units. 1) Among elderly subjects, there is a decrease in the common fluctuations that are observed among the firing rates of motor units in the young. 2) The relationship observed between the firing rate and recruitment threshold of young subjects is disturbed in the elderly. Although in young subjects, at any point in a given submaximal contraction, earlier recruited motor units have higher firing rates than later-recruited units; in aged subjects this dependency of firing rate on recruitment rank is compromised. 3) The progressive decrease observed in the firing rates of concurrently active motor units in constant-force contractions in the young is not seen in the aged. In addition to these original findings, this study provided support for earlier reports of 1) decreased average firing rates probably reflecting the slowing of the muscle, 2) a shift in recruitment thresholds toward lower force levels in line with the shift toward type I fibers, and 3) multiphasic action potential shapes indicative of the reinnervation process that takes place during aging. Taken as a whole, these findings indicate significant age-related modifications in the control properties of human motor units.

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Li, Wei, William M. Doyon et John A. Dani. « Quantitative unit classification of ventral tegmental area neurons in vivo ». Journal of Neurophysiology 107, n^o 10 (15 mai 2012) : 2808–20. http://dx.doi.org/10.1152/jn.00575.2011.

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Neurons in the ventral tegmental area (VTA) synthesize several major neurotransmitters, including dopamine (DA), GABA, and glutamate. To classify VTA single-unit neural activity from freely moving rats, we used hierarchical agglomerative clustering and probability distributions as quantitative methods. After many parameters were examined, a firing rate of 10 Hz emerged as a transition frequency between clusters of low-firing and high-firing neurons. To form a subgroup identified as high-firing neurons with GABAergic characteristics, the high-firing classification was sorted by spike duration. To form a subgroup identified as putative DA neurons, the low-firing classification was sorted by DA D2-type receptor pharmacological responses to quinpirole and eticlopride. Putative DA neurons were inhibited by the D2-type receptor agonist quinpirole and returned to near-baseline firing rates or higher following the D2-type receptor antagonist eticlopride. Other unit types showed different responses to these D2-type receptor drugs. A multidimensional comparison of neural properties indicated that these subgroups often clustered independently of each other with minimal overlap. Firing pattern variability reliably distinguished putative DA neurons from other unit types. A combination of phasic burst properties and a low skew in the interspike interval distribution produced a neural population that was comparable to the one sorted by D2 pharmacology. These findings provide a quantitative statistical approach for the classification of VTA neurons in unanesthetized animals.

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Contessa, Paola, John Letizi, Gianluca De Luca et Joshua C. Kline. « Contribution from motor unit firing adaptations and muscle coactivation during fatigue ». Journal of Neurophysiology 119, n^o 6 (1 juin 2018) : 2186–93. http://dx.doi.org/10.1152/jn.00766.2017.

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The control of motor unit firing behavior during fatigue is still debated in the literature. Most studies agree that the central nervous system increases the excitation to the motoneuron pool to compensate for decreased force contributions of individual motor units and sustain muscle force output during fatigue. However, some studies claim that motor units may decrease their firing rates despite increased excitation, contradicting the direct relationship between firing rates and excitation that governs the voluntary control of motor units. To investigate whether the control of motor units in fact changes with fatigue, we measured motor unit firing behavior during repeated contractions of the first dorsal interosseous (FDI) muscle while concurrently monitoring the activation of surrounding muscles, including the flexor carpi radialis, extensor carpi radialis, and pronator teres. Across all subjects, we observed an overall increase in FDI activation and motor unit firing rates by the end of the fatigue task. However, in some subjects we observed increases in FDI activation and motor unit firing rates only during the initial phase of the fatigue task, followed by subsequent decreases during the late phase of the fatigue task while the coactivation of surrounding muscles increased. These findings indicate that the strategy for sustaining force output may occasionally change, leading to increases in the relative activation of surrounding muscles while the excitation to the fatiguing muscle decreases. Importantly, irrespective of changes in the strategy for sustaining force output, the control properties regulating motor unit firing behavior remain unchanged during fatigue. NEW & NOTEWORTHY This work addresses sources of debate surrounding the manner in which motor unit firing behavior is controlled during fatigue. We found that decreases in the motor unit firing rates of the fatiguing muscle may occasionally be observed when the contribution of coactive muscles increases. Despite changes in the strategy employed to sustain the force output, the underlying control properties regulating motor unit firing behavior remain unchanged during muscle fatigue.

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Yang, Da Wei, Jian Chong Chu, Zi Ming Wang et Wei Bo Li. « Shore-Based Air-Defence Unit Shooting Mode Optimization Model Research ». Applied Mechanics and Materials 543-547 (mars 2014) : 1786–89. http://dx.doi.org/10.4028/www.scientific.net/amm.543-547.1786.

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This paper analyzes the relationship between firing way and firing command way. Using the theory of probability and air defense combat strategy, it describes the concept, characteristics, and its mutual relations between concentration, dispersion, and mixing command in shooting mode, analyzes the influence of different ways of command on group firing efficiency.

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Chanaud, Cheryl M., et Christy L. Ludlow. « Single Motor Unit Activity of Human Intrinsic Laryngeal Muscles during Respiration ». Annals of Otology, Rhinology & ; Laryngology 101, n^o 10 (octobre 1992) : 832–40. http://dx.doi.org/10.1177/000348949210101006.

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Individual motor units in the thyroarytenoid (TA) and cricothyroid (CT) muscles were studied in 10 normal human volunteers during quiet respiration. Both tonic and phasic firing patterns were found in both TA and CT units. The rate of firing was higher during inhalation than during exhalation in phasic TA units and in tonic CT units. Tonically active units had a higher firing frequency than phasically active units in both TA and CT muscles. Phasically active units corresponded with the respiratory cycle, with firing associated with inhalation in both the TA and CT muscles. A variety of firing patterns were found between units in both the TA and CT muscles, and in one subject, units recorded from the same muscle had very different firing patterns. The results suggest that although laryngeal motoneurons are modulated by the respiratory cycle, they do not respond uniformly to respiration.

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Gorassini, Monica, Jaynie F. Yang, Merek Siu et David J. Bennett. « Intrinsic Activation of Human Motoneurons : Possible Contribution to Motor Unit Excitation ». Journal of Neurophysiology 87, n^o 4 (1 avril 2002) : 1850–58. http://dx.doi.org/10.1152/jn.00024.2001.

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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 (≈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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Masakado, Yoshihisa. « Clinical Neurophysiology in Motor Unit Firing Control ». Japanese Journal of Rehabilitation Medicine 59, n^o 3 (18 mars 2022) : 305–12. http://dx.doi.org/10.2490/jjrmc.59.305.

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Pan, Z. S., Y. Zhang et P. A. Parker. « Motor unit power spectrum and firing rate ». Medical & ; Biological Engineering & ; Computing 27, n^o 1 (janvier 1989) : 14–18. http://dx.doi.org/10.1007/bf02442164.

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Kamen, Gary, Sandra Solar Greenstein et Carlo J. De Luca. « Lateral dominance and motor unit firing behavior ». Brain Research 576, n^o 1 (mars 1992) : 165–67. http://dx.doi.org/10.1016/0006-8993(92)90625-j.

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Eken, Torsten. « Spontaneous Electromyographic Activity in Adult Rat Soleus Muscle ». Journal of Neurophysiology 80, n^o 1 (1 juillet 1998) : 365–76. http://dx.doi.org/10.1152/jn.1998.80.1.365.

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Eken, Torsten. Spontaneous electromyographic activity in adult rat soleus muscle. J. Neurophysiol. 80: 365–376, 1998. Single-motor-unit and gross electromyograms (EMG) were recorded from the soleus muscle in six unrestrained rats. The median firing frequencies of nine motor units were in the 16–25 Hz range, in agreement with previous studies. One additional motor unit had a median firing frequency of 47 Hz. This unit and one of the lower-frequency units regularly fired doublets. Motor-unit firing frequency was well correlated to whole-muscle EMG during locomotion. Integrated rectified gross EMG revealed periods of continuous modulation, phasic high-amplitude events, and tonic low-amplitude segments. The tonic segments typically were caused by a small number of motor units firing at stable high frequencies (20–30 Hz) for extended periods of time without detectable activity in other units. This long-lasting firing in single motor units typically was initiated by transient mass activity, which recruited many units. However, only one or a few units continued firing at a stable high frequency. The tonic firing terminated spontaneously or in conjunction with an episode of mass activity. Different units were active in different tonic segments. Thus there was an apparent dissociation between activity in different single motor units and consequently between single-motor-unit activity and whole-muscle EMG. It is proposed that the maintained tonic motor-unit activity is caused by intrinsic motoneuron properties in the form of depolarizing plateau potentials.

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Sokoloff, A. J., et T. C. Cope. « Recruitment of triceps surae motor units in the decerebrate cat. II. Heterogeneity among soleus motor units ». Journal of Neurophysiology 75, n^o 5 (1 mai 1996) : 2005–16. http://dx.doi.org/10.1152/jn.1996.75.5.2005.

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1. On the basis of the orderly activation of motoneurons in a pool, one would predict that motor unit activity and whole muscle force will change at least roughly in parallel: active motor units should continue to fire as net muscle force increases and quiescent motor units should remain inactive as muscle force decreases. We have consistently observed this relationship in our studies of the medial gastrocnemius (MG) muscle, but here we report an uncoupling of the soleus muscle and some of its motor units. 2. Physiological properties and firing behaviors of 20 soleus motor units were characterized in five decerebrate cats with the use of intra-axonal stimulation and recording. Motor unit firing was elicited in reflexes initiated by muscle stretch, nerve stimulation, and mechanical stimulation of the heel. Particular emphasis was placed on the heterogenic reflexes produced in soleus by ramphold-release stretches of the MG muscle. In agreement with previous reports, either net heterogenic excitation or inhibition of the soleus muscle was produced in separate trials of MG stretch. 3. During excitation of soleus in autogenic stretch reflexes and in crossed-extension reflexes, all 20 units were recruited or increased firing, i.e., unit firing was coupled with soleus force. In the other reflexes, however, unit firing and muscle force were uncoupled for 10 of these units. Six tonically active motor units were inhibited during an increase in soleus force produced by MG stretch or by mechanical stimulation of the heel. Four motor units were activated during a decrease in soleus force produced by the same stimuli. 4. Six motor units were studied during both soleus inhibition and excitation evoked by MG stretches. One motor unit was consistently coupled to the soleus muscle response; firing increased during soleus excitation and decreased during inhibition. However, four soleus motor units were inhibited under both conditions, and one unit was excited under both conditions. Thus the firing behavior of five of these six motor units was the same in response to MG stretch, irrespective of the soleus response. 5. The uncoupling was most clearly recognized when tonically active units ceased firing during net excitation of the soleus muscle and when silent units began firing during net inhibition of the soleus muscle. Unit responses were not as striking in all trials of MG stretch (spike number increased or decreased relative to prestretch values by 1-4 spikes), but the responses were consistent across trials; in multiple stretches, spike number commonly either increased or decreased. Intertrial regularity was also observed in units for which firing was coupled with the net reflex response of the soleus muscle. 6. Divergence in the firing of soleus motor units was also observed in three cases in which records were taken simultaneously from two motor units. In one pair, one unit increased and the other decreased firing during MG stretch-evoked inhibition of soleus. In the other two pairs, one unit increased and the other decreased firing when soleus was excited by heel stimulation. In all pairs, the unit that decreased firing under these conditions had the lowest recruitment threshold in response to the soleus stretch. 7. Although all soleus motor units were classified as slow-twitch (type S), variation in their physiological properties bore some relation to firing behavior. Those units recruited during periods of soleus inhibition exhibited among the fastest conduction velocities and contraction times in our sample. In all three unit pairs sampled, the unit expressing decreases in firing had the slower conduction velocity and contraction time. 8. These findings demonstrate that soleus motor units are differentially activated and deactivated by peripheral afferents. (ABSTRACT TRUNCATED)

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Goodall, E. V., K. W. Horch, T. G. McNaughton et C. M. Lybbert. « Analysis of single-unit firing patterns in multi-unit intrafascicular recordings ». Medical & ; Biological Engineering & ; Computing 31, n^o 3 (mai 1993) : 257–67. http://dx.doi.org/10.1007/bf02458045.

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Mesin, Luca. « Motor Unit Discharges from Multi-Kernel Deconvolution of Single Channel Surface Electromyogram ». Electronics 10, n^o 16 (21 août 2021) : 2022. http://dx.doi.org/10.3390/electronics10162022.

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Surface electromyogram (EMG) finds many applications in the non-invasive characterization of muscles. Extracting information on the control of motor units (MU) is difficult when using single channels, e.g., due to the low selectivity and large phase cancellations of MU action potentials (MUAPs). In this paper, we propose a new method to face this problem in the case of a single differential channel. The signal is approximated as a sum of convolutions of different kernels (adapted to the signal) and firing patterns, whose sum is the estimation of the cumulative MU firings. Three simulators were used for testing: muscles of parallel fibres with either two innervation zones (IZs, thus, with MUAPs of different phases) or one IZ and a model with fibres inclined with respect to the skin. Simulations were prepared for different fat thicknesses, distributions of conduction velocity, maximal firing rates, synchronizations of MU discharges, and variability of the inter-spike interval. The performances were measured in terms of cross-correlations of the estimated and simulated cumulative MU firings in the range of 0–50 Hz and compared with those of a state-of-the-art single-kernel algorithm. The median cross-correlations for multi-kernel/single-kernel approaches were 92.2%/82.4%, 98.1%/97.6%, and 95.0%/91.0% for the models with two IZs, one IZ (parallel fibres), and inclined fibres, respectively (all statistically significant differences, which were larger when the MUAP shapes were of greater difference).

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Jang, Jinhwa, Hee-Jin Ha, Yun Bok Kim, Young-Ki Chung et Min Whan Jung. « Effects of Methamphetamine on Single Unit Activity in Rat Medial Prefrontal Cortex In Vivo ». Neural Plasticity 2007 (2007) : 1–9. http://dx.doi.org/10.1155/2007/29821.

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To investigate how neuronal activity in the prefrontal cortex changes in an animal model of schizophrenia, we recorded single unit activity in the medial prefrontal cortex of urethane-anesthetized and awake rats following methamphetamine (MA) administration. Systemic MA injection (4 mg/kg, IP) induced inconsistent changes, that is, both enhancement and reduction, in unit discharge rate, with a subset of neurons transiently (<30 min) elevating their activities. The direction of firing rate change was poorly predicted by the mean firing rate or the degree of burst firing during the baseline period. Also, simultaneously recorded units showed opposite directions of firing rate change, indicating that recording location is a poor predictor of the direction of firing rate change. These results raise the possibility that systemic MA injection induces random bidirectional changes in prefrontal cortical unit activity, which may underlie some of MA-induced psychotic symptoms.

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Moon, Jerald B., Dana R. Collins et John W. Canady. « Single Motor Unit Activity in Levator Veli Palatini during Speech and Nonspeech Tasks ». Cleft Palate-Craniofacial Journal 40, n^o 3 (mai 2003) : 256–62. http://dx.doi.org/10.1597/1545-1569_2003_040_0256_smuail_2.0.co_2.

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Objective This article assesses the control of velar movement by relating observed recruitment patterns of single motor unit activity in levator veli palatini observed during speech and nonspeech tasks in a single subject to intraoral pressure demands. Methods Electromyographic activity was recorded from a single motor unit in levator veli palatini during repetitions of “Say ____ again” with selected consonant-vowel-consonant and consonant-vowel syllables, sustained high pressure consonants, and blowing tasks. Single motor unit firing characteristics (e.g., frequency of occurrence, firing frequency) were related to intraoral air pressures recorded during the sustained consonant and blowing tasks. Results Levator single motor unit activity was always present during the /s/ in “say” and the first and second /s/ in /sis/. Activity was observed less consistently during the production of the /s/ in /sus/, the /p/ in /p Λ/, and the /g/ in “again.” Single motor unit firing frequency ranged from 16.1 Hz to 22 Hz during phrase productions. Recruitment was observed during sustained productions of high-pressure consonants when intraoral pressures exceeded 15 cm H2O. Increases in intraoral air pressure were associated with 25% to 85% increases in single motor unit firing frequencies. During nonspeech blowing tasks, single motor unit activity was observed when intraoral air pressure exceeded approximately 12 cm H2O. Increases in intraoral air pressure were again associated with increased single motor unit firing rates. Conclusions Results showed evidence of both preprogrammed and feedback-controlled responses by levator veli palatini to changes in task intraoral pressure demands.

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Bawa, Parveen N. S. « Motor unit firing during concentric and eccentric contractions ». Medicine & ; Science in Sports & ; Exercise 39, Supplement (mai 2007) : 60. http://dx.doi.org/10.1249/01.mss.0000272665.50036.05.

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Jones, Kelvin E. « Motor unit firing statistics and the Fuglevand model ». Journal of Neurophysiology 94, n^o 3 (septembre 2005) : 2255–57. http://dx.doi.org/10.1152/jn.00430.2005.

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Kamen, Gary, et Carlo J. De Luca. « Unusual motor unit firing behavior in older adults ». Brain Research 482, n^o 1 (mars 1989) : 136–40. http://dx.doi.org/10.1016/0006-8993(89)90550-7.

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Arsov, G. L., S. Beskovski et G. M. Dimirovski. « Microcomputer-Based Firing Unit for Three-Pulse Cycloconverter ». IFAC Proceedings Volumes 25, n^o 8 (juin 1992) : 535–42. http://dx.doi.org/10.1016/s1474-6670(17)54107-5.

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Rosengren, S., et K. P. Weber. « S53 : Single motor unit firing changes in VEMPs ». Clinical Neurophysiology 125 (juin 2014) : S11—S12. http://dx.doi.org/10.1016/s1388-2457(14)50052-1.

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Dorfman, Leslie J., Jane E. Howard et Kevin C. McGill. « Motor unit firing rates and firing rate variability in the detection of neuromuscular disorders ». Electroencephalography and Clinical Neurophysiology 73, n^o 3 (septembre 1989) : 215–24. http://dx.doi.org/10.1016/0013-4694(89)90122-3.

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Liu, Lukai, Paolo Bonato et Edward A. Clancy. « Comparison of methods for estimating motor unit firing rate time series from firing times ». Journal of Electromyography and Kinesiology 31 (décembre 2016) : 22–31. http://dx.doi.org/10.1016/j.jelekin.2016.08.015.

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Tansey, K. E., et B. R. Botterman. « Activation of type-identified motor units during centrally evoked contractions in the cat medial gastrocnemius muscle. II. Motoneuron firing-rate modulation ». Journal of Neurophysiology 75, n^o 1 (1 janvier 1996) : 38–50. http://dx.doi.org/10.1152/jn.1996.75.1.38.

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1. The aim of this study was to examine the nature of motoneuron firing-rate modulation in type-identified motor units during smoothly graded contractions of the cat medial gastrocnemius (MG) muscle evoked by stimulation of the mesencephalic locomotor region (MLR). Motoneuron discharge patterns, firing rates, and the extent of firing-rate modulation in individual units were studied, as was the extent of concomitant changes in firing rates within pairs of simultaneously active units. 2. In 21 pairs of simultaneously active motor units, studied during 41 evoked contractions, the motoneurons' discharge rates and patterns were measured by processing the cells' recorded action potentials through windowing devices and storing their timing in computer memory. Once recruited, most motoneurons increased their firing rates over a limited range of increasing muscle tension and then maintained a fairly constant firing rate as muscle force continued to rise. Most motoneurons also decreased their firing rates over a slightly larger, but still limited, range of declining muscle force before they were derecruited. Although this was the most common discharge pattern recorded, several other interesting patterns were also seen. 3. The mean firing rate for slow twitch (type S) motor units (27.8 imp/s, 5,092 activations) was found to be significantly different from the mean firing rate for fast twitch (type F) motor units (48.4 imp/s, 11,272 activations; Student's t-test, P < 0.001). There was no significant difference between the mean firing rates of fast twitch, fatigue-resistant (type FR) and fast twitch, fatigable (type FF) motor units. When the relationship between motoneuron firing rate and whole-muscle force was analyzed, it was noted that, in general, smaller, lower threshold motor units began firing at lower rates and reached lower peak firing rates than did larger, higher threshold motor units. These results confirm both earlier experimental observations and predictions made by other investigators on the basis of computer simulations of the cat MG motor pool, but are in contrast to motor-unit discharge behavior recorded in some human motor-unit studies. 4. The extent of concomitant changes in firing rate within pairs of simultaneously active motor units was examined to estimate the extent of simultaneous motoneuron firing-rate modulation across the motoneuron pool. A smoothed (5 point sliding average) version of the two motoneurons' instantaneous firing rates was plotted against each other, and the slope and statistical significance of the relationship was determined. In 16 motor-unit pairs, the slope of the motoneurons' firing-rate relationship was significantly distinct from 0. Parallel firing-rate modulation (< 10-fold difference in firing rate change reflected by a slope of > 0.1) was noted only in pairs containing motor units of like physiological type and then only if they were of similar recruitment threshold. 5. Other investigators have demonstrated that changes in a motoneuron's "steady-state" firing rate predictably reflect changes in the amount of effective synaptic current that cell is receiving. The finding in the present study of limited parallel firing-rate modulation between simultaneously active motoneurons would suggest that changes in the synaptic drive to the various motoneurons of the pool is unevenly distributed. This finding, in addition to the findings of orderly motor-unit recruitment and the relationship between motor-unit recruitment threshold and motoneuron firing rate, cannot be adequately accommodated for by the existing models of the synaptic organization in motoneuron pools. Therefore a new model of the synaptic organization within the motoneuron pool has been proposed.

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Wilson, Jessica M., Christopher K. Thompson, Laura C. Miller et Charles J. Heckman. « Intrinsic excitability of human motoneurons in biceps brachii versus triceps brachii ». Journal of Neurophysiology 113, n^o 10 (juin 2015) : 3692–99. http://dx.doi.org/10.1152/jn.00960.2014.

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The intrinsic excitability of spinal motoneurons is mediated in part by the presence of persistent inward currents (PICs), which amplify synaptic input and promote self-sustained firing. Studies using animal models have shown that PICs are greater in extensor motoneurons over flexor motoneurons, but this difference has not yet been demonstrated in humans. The primary objective of this study was to determine whether a similar difference exists in humans by recording from motor units in biceps and triceps brachii during isometric contractions. We compared firing rate profiles of pairs of motor units, in which the firing rate of the lower-threshold “control” unit was used as an indicator of common drive to the higher-threshold “test” unit. The estimated contribution of the PIC was calculated as the difference in firing rate of the control unit at recruitment versus derecruitment of the test unit, a value known as the delta-F (ΔF). We found that ΔF values were significantly higher in triceps brachii (5.4 ± 0.9 imp/s) compared with biceps brachii (3.0 ± 1.4 imp/s; P < 0.001). This difference was still present even after controlling for saturation in firing rate of the control unit, rate modulation of the control unit, and differences in recruitment time between test and control units, which are known to contribute to ΔF variability. We conclude that human elbow flexor and extensor motor units exhibit differences in intrinsic excitability, contributing to different neural motor control strategies between muscle groups.

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Hiraba, K., M. Taira, Y. Sahara et Y. Nakamura. « Single-unit activity in bulbar reticular formation during food ingestion in chronic cats ». Journal of Neurophysiology 60, n^o 4 (1 octobre 1988) : 1333–49. http://dx.doi.org/10.1152/jn.1988.60.4.1333.

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1. Single-unit activity was recorded from 215 neurons in the medial bulbar reticular formation during the masticatory sequence, from intake to deglutition, of 3 kinds of food (cat food pellets, canned fish, and milk) in 8 chronically prepared, unanesthetized, spontaneously respiring cats with their head fixed to a stereotaxic apparatus without pain or pressure. The firing patterns were compared to the simultaneously recorded EMGs of the jaw-closing and -opening muscles and to the jaw movement. 2. Fifty neurons changed their firing patterns during mastication. Nine neurons increased and one neuron decreased or stopped firing coincident with the masticatory sequence without an apparent rhythmical modulation of frequency corresponding with the masticatory rhythm (nonphasic group). The firing pattern of the remaining 40 neurons was modulated in phase with jaw movement (phasic group); 34 neurons either showed a spike burst or attained the highest firing frequency during the jaw-opening phase (opening type), while 6 neurons did so during the jaw-closing phase (closing type). The firing patterns of each neuron were essentially the same regardless of the kind of food ingested, except for 2 opening-type neurons that showed a rhythmical burst during mastication of solid food and tonic activity during lapping milk. 3. For 16 phasic neurons, there were significant correlations between some aspects of the firing pattern and a parameter of the movement during ingestion of solid food and/or milk. With one exception, these relationships did not appear to be due to sensory feedback. 4. We detected a monosynaptic excitatory projection from 3 opening-type neurons to the anterior digastric motoneurons, and monosynaptic inhibitory projections to the temporal or masseter motoneurons from 3 other opening-type neurons, by spike-triggered averaging of the full-wave rectified EMG of the jaw-closing and -opening muscles. No monosynaptic projections from the closing-type neurons or nonphasic group neurons to either jaw-opener or -closer motoneurons were detected. 5. The instantaneous firing frequency of all 3 inhibitor premotor neurons was positively correlated with the opening velocity, and the firing of 2 was also related to the jaw displacement.(ABSTRACT TRUNCATED AT 400 WORDS)

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Kiehn, Ole, et Torsten Eken. « Prolonged Firing in Motor Units : Evidence of Plateau Potentials in Human Motoneurons ? » Journal of Neurophysiology 78, n^o 6 (1 décembre 1997) : 3061–68. http://dx.doi.org/10.1152/jn.1997.78.6.3061.

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Kiehn, O. and T. Eken. Prolonged firing in motor units: evidence of plateau potentials in human motoneurons? J. Neurophysiol. 78: 3061–3068, 1997. Serotonin (5-HT) and norepinephrine-dependent plateau potentials are found in spinal motoneurons in reduced turtle and cat preparations. Triggering the plateau potential by short-lasting synaptic excitation causes a prolonged self-sustained firing, which can be terminated by short-lasting synaptic inhibition. The presence of plateau potentials can also allow neurons to fire in a bistable manner, i.e., shifting between stable low and high firing frequencies. Such a bistable firing behavior has been found in soleus motor units in unrestrained rats. In the present study single motor-unit activity was recorded from low-threshold units in human soleus and tibialis anterior muscles to evaluate whether a bistable firing behavior and/or prolonged firing could be evoked. Vibration of the homonymous muscle tendon (30–100 Hz, 2–10 s) was used as excitatory input to the motoneuron pool. Brief excitation while the muscle was electrically silent induced firing during the vibration and sometimes recruited units into prolonged stable firing outlasting the vibratory stimulus. However, a bistable firing behavior, i.e., vibration-induced maintained shifts between two stable levels of firing, could not be convincingly demonstrated. The reason for this was twofold. First, low-threshold human motor units tended to jump to a “preferred firing range” shortly after voluntary recruitment. This firing range was the same as when units were recruited from silence into prolonged firing by vibration. Below the preferred firing range, maintained firing was unstable and usually only possible when subjects were listening to the spike potentials or had visual force-feedback. Second, vibration when units were firing in the preferred firing range caused a transient increase in firing frequency but no maintained frequency shifts. Recordings from pairs of motor units showed that short-lasting vibration could recruit one unit into prolonged firing, while a second unit, which already fired in its preferred firing range, only transiently increased its firing rate during the vibration. This suggests that the prolonged firing was not the result of an increase in the common synaptic drive to the motoneuron pool. We conclude that a bistable firing behavior as seen in intact rats is probably absent in human low-threshold motor units, but that prolonged firing could be seen in response to short-lasting excitation. This latter phenomenon is compatible with the existence of plateau potentials, which have to have a threshold close to the threshold for sodium spike generation.

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DOMOŃ, Dariusz, Stanisław DUDA et Maciej ŁABNO. « PILICA Anti-Aircraft Rocket-Artillery System - a V-SHROAD System ». Problems of Mechatronics Armament Aviation Safety Engineering 11, n^o 1 (31 mars 2020) : 103–12. http://dx.doi.org/10.5604/01.3001.0014.0290.

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The PILICA Anti-Aircraft Rocket-Artillery System has been developed for the Armed Forces of the Republic of Poland. The PILICA Anti-Aircraft Rocket-Artillery System is composed of: The Command and Control station, the Radiolocating station, six Firing Units along with Artillery Tractors, two Transport Vehicles, and two Ammunition Vehicles. PILICA's task is that of detecting, recognising, and identifying objects, then automatically dividing the tasks and commands for efficient elimination. PILICA’s Firing Unit has autonomous-mode target detection, identification and elimination capabilities (without cooperating with Command and Control) using equipment such as its optoelectronic head and IFF system. In the system operation mode and in cooperation with Command and Control, the Firing Unit and its subsystems ensure the reception of commands/combat tasks in its fire responsibility zone, as well as reporting statuses and the completion of the given combat tasks. Reporting and command reception from the Command and Control station is automated. The Firing Unit can fire using its automatic tracking system, or when operated in manual mode. The Firing unit has been equipped with a portable remote control console, providing the ability to use it remotely. In case of a power supply malfunction in the Firing Unit, it is possible to use it entirely manually, with the use of artillery weapons. The Firing Unit is equipped with a stabilised, optoelectronic day-night head that enables it to work independently of the weapons when it comes to observation and detecting, as well as identifying, objects. The head constitutes not only an element of the guidance system, but also a source of information for the entire System, as the data on the detected and observed objects is exchanged within the entire command network. PILICA is equipped with an unique formation and training system, providing capabilities for training teams on real equipment, with the use of a virtual simulation management system employing the DIS protocol.

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Rich, Christopher, George L. O′Brien et Enzo Cafarelli. « Probabilities Associated With Counting Average Motor Unit Firing Rates in Active Human Muscle ». Canadian Journal of Applied Physiology 23, n^o 1 (1 février 1998) : 87–94. http://dx.doi.org/10.1139/h98-006.

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Motor unit firing rates in human muscle can be determined from recordings made with small-diameter microelectrodes inserted directly into the muscle during voluntary contraction. Frequently, these counts are pooled to give an average motor unit firing rate under a given set of conditions. Since the fibers of one motor unit are dispersed among the cells of several others, it is conceivable that discharge rates can be measured in more than one cell from the same unit. If this occurred frequently, the distribution of firing rates could be influenced by those from units counted more than once. Based on literature values, we made the following assumptions: vastus lateralis contains approximately 300 motor units, with an average innervation ratio of 1500. Muscle cell diameter is about 50 to 100 μm and cells are randomly distributed over a motor unit territory of 10 μm diameter. The recording range of a microelectrode is about 600 μm. Given the distribution of cells normally found in whole human muscle, the probability of recording from two or more cells of the same motor unit at 50% MVC follows a Poisson distribution with a mean of 0.44. This model suggests that although there is a low probability of some duplication in this technique, the extent to which it influences the distribution of average motor unit firing rates is minimal over the entire range of forces produced by vastus lateralis. Key words: probability, motor unit, single unit recording, human muscle, rate coding

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Dwiaji, Yudhi Chandra. « Analisis Pengaruh Co-Firing Biomassa Terhadap Kinerja Peralatan Boiler PLTU Batubara Unit 1 PT. XYZ ». Journal of Applied Mechanical Engineering and Renewable Energy 3, n^o 1 (1 février 2023) : 7–15. http://dx.doi.org/10.52158/jamere.v3i1.445.

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Program co-firing biomassa telah diterapkan di pembangkit listrik oleh PLN untuk mendukung kebijakan yang berkaitan dengan bauran energi terbarukan. Sejauh mana co-firing biomassa terus menerus pada berbagai kondisi beban pembangkit akan mempengaruhi kinerja peralatan boiler tidak diketahui. Tujuan dari penelitian ini adalah untuk memastikan efek dari co-firing biomassa yang sedang berlangsung pada efisiensi peralatan boiler di berbagai skenario beban pembangkit. Pendekatan observasi serta teknik wawancara digunakan untuk mengumpulkan data. Dngan menggunakan perangkat lunak Microsoft Excel secara manual, diharapkan dapat memperoleh nilai perhitungan untuk konsumsi bahan bakar spesifik dan laju panas bersih pembangkit, dimana parameter operasi kinerja peralatan boiler dibandingkan dengan data benchmark atau commissioning. Dari penelitian dihasilkan bahwa performa peralatan boiler (medium speed mill, kipas boiler, air preheater) tidak terpengaruh oleh proses co-firing, dan semua parameternya tetap berada dalam batas yang dapat diterima. Diperoleh juga bahwa aliran motor medium speed mill dan fan boiler yang menurun tidak signifikan dan kinerja peralatan boiler pada saat proses co-firing ternyata menjadi lebih ringan. Dilain sisi terdapat penurunan suhu tungku boiler beserta terjadinya perubahan beban, namun kinerja peralatan boiler masih dalam batas. Rata-rata total biaya produksi turun dari 485.324 Rp/Kwh menjadi 484.585 Rp/Kwh dengan co-firing. Selama penelitian berlangsung, rata-rata net Plant Heat Rate selama proses co-firing turun dari 2862,85 kcal/kwh menjadi 2866,35 kcal/kwh.

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Fatela, Pedro, Goncalo V. Mendonca, António Prieto Veloso, Janne Avela et Pedro Mil-Homens. « Blood Flow Restriction Alters Motor Unit Behavior During Resistance Exercise ». International Journal of Sports Medicine 40, n^o 09 (10 juillet 2019) : 555–62. http://dx.doi.org/10.1055/a-0888-8816.

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AbstractWe aimed to determine whether blood flow restriction (BFR) alters the characteristics of individual motor units during low-intensity (LI) exercise. Eight men (26.0±3.8 yrs) performed 5 sets of 15 knee extensions at 20% of one-repetition maximum (with and without BFR). Maximal isometric voluntary contractions (MVC) were performed before and after exercise to quantify force decrement. Submaximal isometric voluntary contractions were additionally performed for 18 s, matching trapezoidal target-force trajectories at 40% pre-MVC. EMG activity was recorded from the vastus lateralis muscle. Then, signals were decomposed to extract motor unit recruitment threshold, firing rates and action potential amplitudes (MUAP). Force decrement was only seen after LI BFR exercise (–20.5%; p<0.05). LI BFR exercise also induced greater decrements in the linear slope coefficient of the regression lines between motor unit recruitment threshold and firing rate (BFR: –165.1±120.4 vs. non-BFR: –44.4±33.1%, p<0.05). Finally, there was a notable shift towards higher values of firing rate and MUAP amplitude post-LI BFR exercise. Taken together, our data indicate that LI BFR exercise increases the activity of motor units with higher MUAP amplitude. They also indicate that motor units with similar MUAP amplitudes become activated at higher firing rates post-LI BFR exercise.

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De Luca, Carlo J., Jose A. Gonzalez-Cueto, Paolo Bonato et Alexander Adam. « Motor Unit Recruitment and Proprioceptive Feedback Decrease the Common Drive ». Journal of Neurophysiology 101, n^o 3 (mars 2009) : 1620–28. http://dx.doi.org/10.1152/jn.90245.2008.

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It has been documented that concurrently active motor units fire under the control of a common drive. That is, the firing rates show high correlation with near-zero time lag. This degree of correlation has been found to vary among muscles and among contractions performed at different force levels in the same muscle. This study provides an explanation indicating that motor units recruited during a contraction cause an increase in the variation (SD) and a decrease in the degree (amplitude) of the correlation of the firing rates. The degree of correlation is lower in muscles having greater spindle density. This effect appears to be mediated by the proprioceptive feedback from the spindles and possibly the Golgi tendon organs. Muscle spindles in particular respond to the mechanical excitation of the nonfused muscle fibers and provide a discordant excitation to the homonymous motoneurons, resulting in a decrease in the correlation of the firing rates of motor units. The implication of this work is that the decreased correlation of the firing rates in some muscles is not necessarily an indication of a decreased common drive from the CNS, but rather an inhibitory influence of the proprioceptive feedback from the peripheral nervous system. This explanation is useful for understanding various manifestations of the common drive reported in the literature.

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Jones, Kelvin E., et Parveen Bawa. « Responses of human motoneurons to la inputs : effects of background firing rate ». Canadian Journal of Physiology and Pharmacology 73, n^o 9 (1 septembre 1995) : 1224–34. http://dx.doi.org/10.1139/y95-174.

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The effects of synchronous Ia volleys on the firing probability of repetitively firing human motoneurons were examined at fast and slow firing rates. Ia afferents of either the median or the posterior tibial nerve were stimulated, while single motor unit activity was recorded from the homonymous muscles. Motoneuron responses to the Ia inputs were quantified by measurement of the magnitude of the short latency excitatory peak in peristimulus time histograms (PSTHs). When the stimuli were given at random with respect to the times of motor unit spikes, the magnitude of the PSTH peak (response probability) was significantly lower at a faster firing rate. In the "triggered" mode of stimulation, stimuli were given at various known times during the interspike interval. In this mode the response probability to the input increased monotonically as the stimuli were delivered progressively later during the interspike interval. The response probability at a fixed delay with respect to the triggering spike was higher at the faster firing rate. The results obtained with the two modes of stimulation are not in contradiction and both may be explained by the nature of membrane voltage trajectories and ionic conductances during the interspike interval described for repetitively firing cat motoneurons.Key words: motor unit, H-reflex, flexor carpi radialis, soleus, afterhyperpolarization, excitatory postsynaptic potential.

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Kline, Joshua C., et Carlo J. De Luca. « Error reduction in EMG signal decomposition ». Journal of Neurophysiology 112, n^o 11 (1 décembre 2014) : 2718–28. http://dx.doi.org/10.1152/jn.00724.2013.

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Decomposition of the electromyographic (EMG) signal into constituent action potentials and the identification of individual firing instances of each motor unit in the presence of ambient noise are inherently probabilistic processes, whether performed manually or with automated algorithms. Consequently, they are subject to errors. We set out to classify and reduce these errors by analyzing 1,061 motor-unit action-potential trains (MUAPTs), obtained by decomposing surface EMG (sEMG) signals recorded during human voluntary contractions. Decomposition errors were classified into two general categories: location errors representing variability in the temporal localization of each motor-unit firing instance and identification errors consisting of falsely detected or missed firing instances. To mitigate these errors, we developed an error-reduction algorithm that combines multiple decomposition estimates to determine a more probable estimate of motor-unit firing instances with fewer errors. The performance of the algorithm is governed by a trade-off between the yield of MUAPTs obtained above a given accuracy level and the time required to perform the decomposition. When applied to a set of sEMG signals synthesized from real MUAPTs, the identification error was reduced by an average of 1.78%, improving the accuracy to 97.0%, and the location error was reduced by an average of 1.66 ms. The error-reduction algorithm in this study is not limited to any specific decomposition strategy. Rather, we propose it be used for other decomposition methods, especially when analyzing precise motor-unit firing instances, as occurs when measuring synchronization.

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Del Valle, Alejandro, et Christine K. Thomas. « Motor unit firing rates during isometric voluntary contractions performed at different muscle lengths ». Canadian Journal of Physiology and Pharmacology 82, n^o 8-9 (1 juillet 2004) : 769–76. http://dx.doi.org/10.1139/y04-084.

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Firing rates of motor units and surface EMG were measured from the triceps brachii muscles of able-bodied subjects during brief submaximal and maximal isometric voluntary contractions made at 5 elbow joint angles that covered the entire physiological range of muscle lengths. Muscle activation at the longest, midlength, and shortest muscle lengths, measured by twitch occlusion, averaged 98%, 97%, and 93% respectively, with each subject able to achieve complete activation during some contractions. As expected, the strongest contractions were recorded at 90° of elbow flexion. Mean motor unit firing rates and surface EMG increased with contraction intensity at each muscle length. For any given absolute contraction intensity, motor unit firing rates varied when muscle length was changed. However, mean motor unit firing rates were independent of muscle length when contractions were compared with the intensity of the maximal voluntary contraction (MVC) achieved at each joint angle.Key words: muscle activation, length–tension relationships, force–frequency relationships.

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Dacko, S. M., A. J. Sokoloff et T. C. Cope. « Recruitment of triceps surae motor units in the decerebrate cat. I. Independence of type S units in soleus and medial gastrocnemius muscles ». Journal of Neurophysiology 75, n^o 5 (1 mai 1996) : 1997–2004. http://dx.doi.org/10.1152/jn.1996.75.5.1997.

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1. We tested the hypothesis that reflex inhibition of soleus motor units reflects selective inhibition of slow-twitch (type S) motor units throughout the triceps surae. Physiological properties including type, together with firing behavior, were measured from single motor units in the medial gastrocnemius (MG) muscle of decerebrate cats with the use of intra-axonal recording and stimulation. MG unit firing was contrasted during net inhibition or excitation of the slow-twitch soleus muscle produced by ramp-hold-release stretches of MG. 2. Stretch of the MG muscle increased the firing of type S motor units in the MG regardless of the reflex response of the soleus muscle. When stretch inhibited soleus, each of the 14 type S units sampled from MG either was newly recruited or exhibited increases in the rate of ongoing firing. Increased firing was observed in 320 of 321 stretch trials. For 8 of these 14 units, a total of 155 stretch trials evoked reflex excitation of soleus, and unit firing increased in all trials. 3. For the eight MG type S motor units studied during both reflex inhibition and excitation of soleus, firing rate tended to be higher during inhibition. The higher rates were also associated with the higher MG forces required to elicit soleus inhibition. For one MG type S unit it was possible to compare firing rates during soleus inhibition and excitation for trials of overlapping levels of MG force. For this unit, firing rate was similar, but still appreciably higher, during inhibition. 4. Soleus inhibition was also produced by stretch of the plantaris (PL) or lateral gastrocnemius (LG) muscles. Type S units in PL (n = 2) or in LG (n = 1) were recruited or increased firing rate even when stretch of these muscles produced soleus inhibition. 5. The firing behavior of 12 fast-twitch (type F) units was studied (11 from MG, 1 from PL). All type F units either were recruited or accelerated the rate of firing during soleus inhibition, as well as during soleus excitation. 6. These findings give evidence that reflex inhibition of type S motor units in the soleus muscle does not necessarily reflect an organizational scheme in which there is inactivation of type S units in other active muscles. In the DISCUSSION we point out the absence of direct evidence for selective inactivation of units on the basis of their type classification.

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Trevino, Michael A., Trent J. Herda, Andrew C. Fry, Philip M. Gallagher, John P. Vardiman, Eric M. Mosier et Jonathan D. Miller. « Influence of the contractile properties of muscle on motor unit firing rates during a moderate-intensity contraction in vivo ». Journal of Neurophysiology 116, n^o 2 (1 août 2016) : 552–62. http://dx.doi.org/10.1152/jn.01021.2015.

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It is suggested that firing rate characteristics of motor units (MUs) are influenced by the physical properties of the muscle. However, no study has correlated MU firing rates at recruitment, targeted force, or derecruitment with the contractile properties of the muscle in vivo. Twelve participants (age = 20.67 ± 2.35 yr) performed a 40% isometric maximal voluntary contraction of the leg extensors that included linearly increasing, steady force, and decreasing segments. Muscle biopsies were collected with myosin heavy chain (MHC) content quantified, and surface electromyography (EMG) was recorded from the vastus lateralis. The EMG signal was decomposed into the firing events of single MUs. Slopes and y-intercepts were calculated for 1) firing rates at recruitment vs. recruitment threshold, 2) mean firing rates at steady force vs. recruitment threshold, and 3) firing rates at derecruitment vs. derecruitment threshold relationships for each subject. Correlations among type I %MHC isoform content and the slopes and y-intercepts from the three relationships were examined. Type I %MHC isoform content was correlated with MU firing rates at recruitment ( y-intercepts: r = −0.577; slopes: r = 0.741) and targeted force (slopes: r = 0.853) vs. recruitment threshold and MU firing rates at derecruitment ( y-intercept: r = −0.597; slopes: r = 0.701) vs. derecruitment threshold relationships. However, the majority of the individual MU firing rates vs. recruitment and derecruitment relationships were not significant ( P > 0.05) and, thus, revealed no systematic pattern. In contrast, MU firing rates during the steady force demonstrated a systematic pattern with higher firing rates for the lower- than higher-threshold MUs and were correlated with the physical properties of MUs in vivo.

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Kamen, Gary. « Aging, Resistance Training, and Motor Unit Discharge Behavior ». Canadian Journal of Applied Physiology 30, n^o 3 (1 juin 2005) : 341–51. http://dx.doi.org/10.1139/h05-126.

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Researchers have alluded to the existence of "neural factors" in the expression and development of muscular strength. Candidate neural factors including motor unit recruitment, rate coding, doublet firing, and motor unit synchronization are discussed in this review. Aging is generally accompanied by lower motor unit discharge rates. However, both young and older adults exhibit rapid changes in muscular strength with repeated strength testing. These strength changes occur with concomitant albeit transient increases in motor unit discharge rate. These and other neural factors may contribute to the initial increases in muscular strength observed during the early phases of resistance exercise training. Key words: firing rate, muscle, exercise

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Hu, Xiaogang, William Z. Rymer et Nina L. Suresh. « Motor unit pool organization examined via spike-triggered averaging of the surface electromyogram ». Journal of Neurophysiology 110, n^o 5 (1 septembre 2013) : 1205–20. http://dx.doi.org/10.1152/jn.00301.2012.

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Voluntary muscle force control is accomplished both by recruitment of motor units (MUs) and by firing rate modulation of active MUs. Typically, MU recruitment and firing rate organization is assessed using piecemeal intramuscular recordings drawn from different experiments, or even from different subjects. As a consequence, it is often difficult to assemble a systematic description of the relations between the different MU properties relevant to the control of muscle force. To address this gap, the objective of our current study was to characterize recruitment and firing rate organization of multiple MUs of differing action potential size, recorded simultaneously from the first dorsal interosseous muscle of intact human subjects, using a recently developed surface electromyogram (EMG) sensor array recording and decomposition system (Delsys). We sought to assess the relation between putative MU size and the recruitment and firing properties for these MUs, recorded at different muscle contraction levels. Spike-triggered averaging (STA) of the surface EMG was performed to estimate the action potential sizes using the firing times of discriminated MUs as the event triggers. The results show that the size principle, which relates MU size to recruitment rank order, was clearly evident during individual force contractions. In addition, the mean firing rate across MUs decreased with increasing size of the MU action potential and was also inversely proportional to the recruitment threshold force. We propose that surface EMG recordings together with advanced decomposition systems, combined with STA methods, may provide an efficient way to systematically examine MU pool organizational properties.

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