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Littérature scientifique sur le sujet « Contractile units »

Auteur : Grafiati

Publié le 14 mars 2023

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Articles de revues sur le sujet "Contractile units"

Ali, Farah, Peter D. Paré et Chun Y. Seow. « Models of contractile units and their assembly in smooth muscle ». Canadian Journal of Physiology and Pharmacology 83, n^o 10 (1 octobre 2005) : 825–31. http://dx.doi.org/10.1139/y05-052.

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It is believed that the contractile filaments in smooth muscle are organized into arrays of contractile units (similar to the sarcomeric structure in striated muscle), and that such an organization is crucial for transforming the mechanical activities of actomyosin interaction into cell shortening and force generation. Details of the filament organization, however, are still poorly understood. Several models of contractile filament architecture are discussed here. To account for the linear relationship observed between the force generated by a smooth muscle and the muscle length at the plateau of an isotonic contraction, a model of contractile unit is proposed. The model consists of 2 dense bodies with actin (thin) filaments attached, and a myosin (thick) filament lying between the parallel thin filaments. In addition, the thick filament is assumed to span the whole contractile unit length, from dense body to dense body, so that when the contractile unit shortens, the amount of overlap between the thick and thin filaments (i.e., the distance between the dense bodies) decreases in exact proportion to the amount of shortening. Assembly of the contractile units into functional contractile apparatus is assumed to involve a group of cells that form a mechanical syncytium. The contractile apparatus is assumed malleable in that the number of contractile units in series and in parallel can be altered to accommodate strains on the muscle and to maintain the muscle's optimal mechanical function.Key words: contraction model, ultrastructure, length adaptation, plasticity.

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Thomas, C. K., R. S. Johansson et B. Bigland-Ritchie. « Attempts to physiologically classify human thenar motor units ». Journal of Neurophysiology 65, n^o 6 (1 juin 1991) : 1501–8. http://dx.doi.org/10.1152/jn.1991.65.6.1501.

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1. This study was designed to determine whether human thenar motor units can be classified into types by the same physiological criteria used for other mammalian limb motor units and to consider whether such classification is functionally relevant. 2. Contractile responses of 25 human thenar single motor units were examined when their motor axons were stimulated intraneurally at rates from 1 to 100 Hz and intermittently at 40 Hz in a conventional 2-min fatigue test. Twitch and tetanic forces were measured together with various indexes of contractile rate. 3. Twitch contraction times and subtetanic to maximum tetanic force ratios were both distributed continuously. "Sag" in tension was not evident in unfused force profiles. Thus these units could not be divided into fast and slow types by the use of traditional contractile rate criteria. 4. Most units were fatigue resistant, with force fatigue indexes (FI) ranging from 0.33 to 1.14. None could be classified as fatiguable (FI less than 0.25). Seven units (28%) fell into the fatigue-intermediate (FI = 0.25-0.75) category, whereas 18 units (72%) had FI greater than 0.75, i.e., they were fatigue-resistant units. However, these units could not be classified by conventional FI and contractile rate criteria, because fatigue-resistant and fatigue-intermediate units had similar contractile rates. 5. Additional FI were calculated to describe changes in contractile rate. During the fatigue test, units behaved in one of three ways, showing 1) little change in either force or rate; 2) contractile slowing during the contraction and relaxation phases, with little or no force loss; or 3) both force and rate reduction.(ABSTRACT TRUNCATED AT 250 WORDS)

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Mateika, J. H., E. G. Essif, C. Dellorusso et R. F. Fregosi. « Contractile Properties of Human Nasal Dilator Motor Units ». Journal of Neurophysiology 79, n^o 1 (1 janvier 1998) : 371–78. http://dx.doi.org/10.1152/jn.1998.79.1.371.

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Mateika, J. H., E. G. Essif, C. DelloRusso, and R. F. Fregosi. Contractile properties of human nasal dilator motor units. J. Neurophysiol. 79: 371–378, 1998. The technique of intramuscular microstimulation was used to activate facial nerve fibers while acquiring simultaneous twitch force measurements to measure the contractile properties and force-frequency responses of human nasal dilator (ND) motor units. Twitch force amplitude (TF), contraction time (CT), half-relaxation time (HRT), and the maximal rate of rise of force normalized to the peak force (maximum contraction rate, MCR) were recorded from 98 ND motor units in 37 subjects. The average CT, HRT, MCR, and TF were 47.9 ± 1.8 ms, 42.6 ± 2.1 ms, 28.6 ± 1.8 s−1, and 1.06 ± 0.1 mN, respectively. Neither CT nor HRT were significantly correlated with TF. The average CT and HRT were similar to values recorded for small muscles of the hand but were faster than the values recorded from human toe extensor motor units. However the lack of an association between twitch force and CT or HRT was similar to the findings obtained for both human hand and foot muscles. Force-frequency curves were recorded from eight ND motor units. The force produced by the eight motor units was recorded in response to stimuli delivered at 1, 5, 10, 15, 20, 25, 30, 35, and 40 Hz to assess force-frequency relationships. The mean twitch force of the eight motor units was 0.91 ± 0.3 mN and the average tetanic force was 8.1 ± 1.8 mN. Therefore the average twitch force was equal to 12.7% of the tetanic force. Fifty percent of the unit tetanic force was achieved at an average frequency of 16.4 ± 1.7 Hz, which is greater than the value recorded for human toe extensor motor units (9.6 Hz). Thus the force produced by the ND motor units was more sensitive to changes in discharge frequency over the range of ∼10–30 Hz and less sensitive to changes in the range of 0–10 Hz because of their fast contractile properties. The mean slope of the regression lines that were fit to the steep portion of each force-frequency curve was 5.15 ± 0.5% change in force/Hz. This value was greater than the slope measured for human toe extensor muscles (4.2% change in force/Hz). These observations suggest that force gradation by ND motor units is more sensitive to changes in stimulation frequency than human toe extensor motor units. We conclude that most ND motor units have fast contractile properties and that rate coding may play a significant role in the gradation of force produced by the ND muscle. Furthermore, the findings of this investigation have demonstrated that contractile speed and TF in a human facial muscle are not correlated. This supports previous findings obtained from human hand and foot muscles and suggests that there may be a fundamental difference in the contractile speed-twitch force relationship between many human muscles and most muscles of other mammals.

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Doherty, Timothy J., et William F. Brown. « Age-related changes in the twitch contractile properties of human thenar motor units ». Journal of Applied Physiology 82, n^o 1 (1 janvier 1997) : 93–101. http://dx.doi.org/10.1152/jappl.1997.82.1.93.

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Doherty, Timothy J., and William F. Brown. Age-related changes in the twitch contractile properties of human thenar motor units. J. Appl. Physiol. 82(1): 93–101, 1997.—The purpose of this study was to examine the effects of aging on the contractile and electrophysiological properties of human thenar motor units (MUs). Percutaneous electrical stimulation of single motor axons within the median nerve was used to isolate and examine the twitch tensions, contractile speeds, and surface-detected MU action potential (S-MUAP) sizes of 48 thenar MUs in 17 younger subjects (25–53 yr) and 44 thenar MUs in 9 older subjects (64–77 yr). A wide range of twitch tensions, contractile speeds, and S-MUAP sizes was observed in both age groups. However, older subjects had significantly larger MU twitch tensions and slower MU twitch contraction and half-relaxation times. These changes were accompanied by increased S-MUAP sizes. These findings suggest that the human thenar MU pool undergoes significant age-related increase in MU size and slowing of contractile speed. Such adaptation may help to overcome previously reported age-related losses of thenar MUs.

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Foehring, R. C., G. W. Sypert et J. B. Munson. « Properties of self-reinnervated motor units of medial gastrocnemius of cat. I. Long-term reinnervation ». Journal of Neurophysiology 55, n^o 5 (1 mai 1986) : 931–46. http://dx.doi.org/10.1152/jn.1986.55.5.931.

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This work tested whether the membrane electrical properties of cat motoneurons, the contractile properties of their muscle units, and the normal relationships among them would be restored 9 mo after section and resuture of their muscle nerve. Properties of medial gastrocnemius (MG) motor units were examined 9 mo following section and resuture of the MG nerve in adult cats. Motoneuron electrical properties and muscle-unit contractile properties were measured. Motor units were classified on the basis of their contractile properties as type fast twitch, fast fatiguing (FF), fast twitch with intermediate fatigue resistance (FI), fast twitch, fatigue resistant (FR), or slow twitch, fatigue resistant (S) (8, 20). Muscle fibers were classified as type fast glycolytic (FG), fast oxidative glycolytic (FOG), or slow oxidative (SO) on the basis of histochemical staining for myosin adenosine triphosphatase, nicotinamide adenine dinucleotide diaphorase, and alpha-glycerophosphate dehydrogenase (48). Following 9 mo self-reinnervation, the proportions of each motor-unit type were the same as in normal control animals. Motoneuron membrane electrical properties [axonal conduction velocity, afterhyperpolarization (AHP) half-decay time, rheobase, and input resistance] also returned to control levels in those motoneurons that made functional reconnection with the muscle (as determined by ability to elicit measurable tension). The relationships among motoneuron electrical properties were normal in motoneurons making functional reconnection. Approximately 10% of MG motoneurons sampled did not elicit muscle contraction. These cells' membrane electrical properties were different from those that did elicit muscle contraction. Contractile speed and fatigue resistance of reinnervated muscle units had recovered to control levels at 9 mo postoperation. Force generation did not recover fully in type-FF units. The reduced tensions were apparently due to failure of recovery of FG muscle fiber area. Following reinnervation, relationships between motoneuron electrical and muscle-unit contractile properties were similar to controls. This was reflected in a degree of correspondence between motor-unit type and motoneuron type similar to normal units (84 vs. 86%, as defined by Ref. 61). There was a significantly increased proportion of type-SO muscle fibers and a decrease in the fast muscle fibers (especially type FOG) in 9 mo reinnervated MG. Together with the unchanged proportions of motor-unit types, this led to an estimate of average innervation ratios being increased in type-S motor units and decreased in type-FR units.(ABSTRACT TRUNCATED AT 400 WORDS)

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Sutlive, Thomas G., J. Ross McClung et Stephen J. Goldberg. « Whole-Muscle and Motor-Unit Contractile Properties of the Styloglossus Muscle in Rat ». Journal of Neurophysiology 82, n^o 2 (1 août 1999) : 584–92. http://dx.doi.org/10.1152/jn.1999.82.2.584.

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Investigations of whole muscle and motor-unit contractile properties have provided valuable information for our understanding of the spinal cord and extraocular motor systems. However, no previous investigation has examined these properties in an isolated tongue muscle. The purpose of this study was to determine the contractile properties and muscle fiber types of the rat styloglossus muscle. The styloglossus is one of three extrinsic tongue muscles and serves to retract the tongue within the oral cavity. Adult male Sprague-Dawley rats ( n = 19) were used in these experiments. The contractile characteristics of the whole styloglossus muscle ( n = 9) were measured in response to stimulation of the hypoglossal nerve branch to the muscle. The average twitch tension produced was 3.30 g with a mean twitch contraction time of 13.81 ms. The mean maximum tetanic tension was 19.66 g and occurred at or near the fusion frequency, which averaged 109 Hz. The styloglossus muscle was resistant to fatigue [fatigue index (F. I.) = 0.76]. In separate experiments ( n = 7), the contractile characteristics of 37 single motor units were measured in response to extracellular stimulation of hypoglossal motoneurons. The twitch tension generated by styloglossus motor units averaged 35.7 mg, and the mean twitch contraction time was 12.46 ms. The mean fusion frequency was 92 Hz. Maximum tetanic tension averaged 177.8 mg. Styloglossus single motor units were resistant to fatigue (F. I. = 0.74). The sites of stimulation that yielded a contractile response in the styloglossus muscle were consistent with the location of the styloglossus motoneuron pool reported in earlier anatomy studies. Muscle fiber typing was determined in three animals based on the myofibrillar ATPase reaction at pH 9.8, 4.6, and 4.3. The styloglossus muscle was composed of ≈99% type IIA fibers with a few scattered type I fibers present in the study sample. On the basis of the combined findings of the physiology and histochemistry experiments, the styloglossus muscle appeared to be a homogeneous muscle composed almost exclusively of fast, fatigue-resistant motor units. These properties of the styloglossus muscle and its motor units were compared with findings in other rat skeletal muscles.

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Łochyński, Dawid, Dominik Kaczmarek, Włodzimierz Mrówczyński, Wojciech Warchoł, Joanna Majerczak, Janusz Karasiński, Michał Korostyński, Jerzy A. Zoladz et Jan Celichowski. « Contractile properties of motor units and expression of myosin heavy chain isoforms in rat fast-type muscle after volitional weight-lifting training ». Journal of Applied Physiology 121, n^o 4 (1 octobre 2016) : 858–69. http://dx.doi.org/10.1152/japplphysiol.00330.2016.

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Dynamic resistance training increases the force and speed of muscle contraction, but little is known about modifications to the contractile properties of the main physiological types of motor units (MUs) that contribute to these muscle adaptations. Although the contractile profile of MU muscle fibers is tightly coupled to myosin heavy chain (MyHC) protein expression, it is not well understood if MyHC transition is a prerequisite for modifications to the contractile characteristics of MUs. In this study, we examined MU contractile properties, the mRNA expression of MyHC, parvalbumin, and sarcoendoplasmic reticulum Ca2+pump isoforms, as well as the MyHC protein content after 5 wk of volitional progressive weight-lifting training in the medial gastrocnemius muscle in rats. The training had no effect on MyHC profiling or Ca2+-handling protein gene expression. Maximum force increased in slow (by 49%) and fast (by 21%) MUs. Within fast MUs, the maximum force increased in most fatigue-resistant and intermediate but not most fatigable MUs. Twitch contraction time was shortened in slow and fast fatigue-resistant MUs. Twitch half-relaxation was shortened in fast most fatigue-resistant and intermediate MUs. The force-frequency curve shifted rightward in fast fatigue-resistant MUs. Fast fatigable MUs fatigued less within the initial 15 s while fast fatigue-resistant units increased the ability to potentiate the force within the first minute of the standard fatigue test. In conclusion, at the early stage of resistance training, modifications to the contractile characteristics of MUs appear in the absence of MyHC transition and the upregulation of Ca2+-handling genes.

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Łochyński, Dawid, Marcin Bączyk, Dominik Kaczmarek, Maria Jolanta Rędowicz, Jan Celichowski et Piotr Krutki. « Adaptations in physiological properties of rat motor units following 5 weeks of whole-body vibration ». Applied Physiology, Nutrition, and Metabolism 38, n^o 9 (septembre 2013) : 913–21. http://dx.doi.org/10.1139/apnm-2012-0478.

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The purpose of the study was to determine the effects of 5-week whole-body vibration (WBV) on contractile parameters and force–frequency relationship of functionally isolated motor units of the rat medial gastrocnemius muscle: fast fatigable (FF), fast fatigue-resistant (FR), and slow (S). Moreover, myosin heavy chain isoform content was quantified. Following WBV, the maximum tetanic force of FF units was increased by ∼25%. The twitch half-relaxation time in all types of motor units and the twitch contraction time in FR units were shortened. The twitch-to-tetanus force ratio was decreased and the force–frequency curves were shifted rightwards in S and FR units. Myosin heavy chain distribution was not changed. These findings suggest modifications of the excitation–contraction coupling towards shortening of a twitch contraction. The observed increase in force of FF units may contribute to gains in muscle dynamic strength reported following WBV treatment.

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Klass, M., S. Baudry et J. Duchateau. « Contractile properties of single motor units in elderly ». Computer Methods in Biomechanics and Biomedical Engineering 8, sup1 (septembre 2005) : 167–68. http://dx.doi.org/10.1080/10255840512331388786.

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Nelson, J. S., S. J. Goldberg et J. R. McClung. « Motoneuron electrophysiological and muscle contractile properties of superior oblique motor units in cat ». Journal of Neurophysiology 55, n^o 4 (1 avril 1986) : 715–26. http://dx.doi.org/10.1152/jn.1986.55.4.715.

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Intracellular techniques were used to study single motor units of the trochlear nucleus and superior oblique muscle in the cat. Motoneuron electrophysiological properties were correlated with muscle-unit contractile characteristics assessed under isometric conditions. Two distinct motor-unit types were identified and designated as twitch and nontwitch. Nontwitch units made up 5% of the total population studied. They responded only to tetanic stimulation with graded force that increased as stimulus frequency was increased up to 300-400 Hz. These units made up a homogeneous population in that they were innervated by slowly conducting axons, produced weak tetanic tensions, and were extremely fatigue resistant. Twitch units made up the majority (95%) of units studied. These units responded to single pulse stimulation with typical twitch contractions. The contraction speed and tension ranges for these units were comparable with those obtained from other extraocular muscle single units. Superior oblique twitch units, mechanically comparable with multiply innervated conducting units, identified in the cat inferior oblique muscle (31) were not observed. The twitch-unit population was heterogeneous in terms of neuromuscular fatigue resistance. Unit fatigability was inversely related to maximal tetanic tension. Motoneuron conduction velocity was related to muscle-unit contractile properties in a way similar to that seen in extremity motor units. The slowest twitch units were weak, fatigue resistant, and innervated by slow conducting axons. The fastest units were, in general, innervated by faster conducting axons, produced greater tetanic tensions, and were more susceptible to fatigue. Correlations among input resistance, rheobase, and conduction velocity were also observed. At present, subdivisions of the twitch-unit population on the basis of any one or combination of unit properties does not seem appropriate.

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Thèses sur le sujet "Contractile units"

Murtada, Sae-Il. « Smooth muscle modeling activation and contraction of contractile units in smooth muscle / ». Licentiate thesis, Stockholm : Skolan för teknikvetenskap, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11349.

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Liu, Jeffrey Chao-Yu. « Length distribution of myosin filaments in smooth muscle and implications in the structure and function of contractile units ». Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/52272.

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Smooth muscle is an essential component of the walls of numerous hollow or tubular organs throughout the body, including blood vessels, airways, and the bladder. Proper physiological functioning of these organs relies heavily on the appropriate activation and contraction of the smooth muscle tissue. Pathophysiological conditions may arise from both excessive and insufficient smooth muscle contraction. Muscle function is closely associated with muscle structure. More specifically, during a contraction, cyclic interactions between myosin cross-bridges and actin filaments allow for muscle shortening and force generation. Myosin molecules from smooth muscle and non-muscle cells are known to self-assemble into side-polar filaments in vitro. However the in situ mechanism of filament assembly is not clear and the question of whether there is a unique length for myosin filaments in smooth muscle is still under debate. In this study we measured the lengths of 16,587 myosin filaments in three types of smooth muscle cells using serial electron microscopy (EM). Sheep airway and pulmonary arterial smooth muscle as well as rabbit carotid arterial smooth muscle were fixed for EM and serial ultra-thin (50-60 nm) sections were obtained. Myosin filaments were traced in consecutive sections to determine their lengths. The results indicate that there is not a single length for the myosin filaments; instead there is a wide variation in lengths. The plots of observation frequency versus myosin filament length follow an exponential decay pattern. The most significant finding of this study is that myosin filaments in smooth muscle do not have a uniform length and analysis suggests that the distribution of filament length is a result of a dynamic equilibrium between polymerization and de-polymerization of myosin molecules driven by predictable probabilities of the myosin dimers to bind with and dissociate from each other.
Medicine, Faculty of
Medicine, Department of
Experimental Medicine, Division of
Graduate

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Querceto, Silvia. « Biomimetic materials for novel cardiac regeneration approaches ». Doctoral thesis, Università di Siena, 2022. http://hdl.handle.net/11365/1211514.

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The quest for novel biomaterials to promote cell structural and functional maturation for cardiac tissue regeneration has emphasized a need to create microenvironments with physiological features. Substrate stiffness constitutes a structural property of crucial importance in the field of tissue engineering and many studies have shown how cardiac cells sense the rigidity of the substrate on which they grow. In this work, we focused on the relevance of substrates mimicking cardiac extracellular matrix (cECM) rigidity for the understanding of the complex interplay between the extracellular and intracellular compartments. Among the most promising biomaterials, Liquid Crystalline Elastomers (LCEs) represent a novel class of polymers previously investigated both as artificial muscles for biomedical purposes and dynamic cell scaffolds. The development of new smart materials which can provide bioactive cues to control and regulate cell fate has been recently encouraged. Indeed, mechanical cues play a significant role in maintaining cell and tissues/organs functions and, in this respect, cell models and substrate stiffness appear as intriguing tools for the investigation of cECM-cell interactions both in physiological and pathological conditions. From the perspective of materials, we have explored the fabrication of biomimetic patterned substrates to direct human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) growth and evaluate their effect on cell functional properties. In the field of regenerative medicine, the advent of hiPSC-CMs has paved the way for a patient-specific therapy but the development of more mature hiPSC-CMs is still needed. Promising approaches that have begun to be investigated include long-term culture, mechanical loading, 3-dimensional tissue engineering and, above all, the use of dynamic scaffolds to boost cell maturation by giving a mechanical stimulus. Finally, with the aim of creating an effective dynamic cell substrate, we have introduced the design of the first prototype of LCE-based biomimetic contractile unit by optimizing a miniaturization of the mechanical device. The functional properties of the contractile apparatus have been investigated and then modulated to closely reproduce the features of native myocardium. Overall, in this work we have provided an overview of some functional aspects of biomaterials which are considered of key relevance in different biomedical fields to elucidate how recent advances may impact future tissue engineering applications.

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Klass, Malgorzata. « Contribution à l'étude de l'effet du vieillissement sur la fonction neuromusculaire ». Doctoral thesis, Universite Libre de Bruxelles, 2007. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209224.

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Résumé en français :

L’objectif de nos investigations a été d’étudier, chez le sujet humain, les mécanismes responsables de l'altération des performances motrices au cours du vieillissement. La première étude était destinée d’une part, à comparer la diminution maximale de force observée dans les différents régimes de contraction et, d’autre part, à contribuer à la compréhension des mécanismes à l’origine de la meilleure préservation de force pour le régime excentrique. Etant donné que jusqu’à présent, seuls des facteurs musculaires avaient été proposés afin d’expliquer les différences existant en fonction du régime de contraction, nous nous sommes plus particulièrement intéressés à une éventuelle participation de facteurs nerveux.

Dans la seconde étude, nous avons testé de manière indirecte (via l’enregistrement d’activités réflexes) l’efficacité des afférences périphériques au cours du vieillissement. En effet, sous le contrôle de la commande centrale, celles-ci contribuent également à réguler le niveau d’excitabilité des motoneurones. Une moindre efficacité de celles-ci pourrait donc être un facteur supplémentaire responsable de l’altération de la fonction motrice.

Nous avons ensuite analysé (études III et IV) les propriétés contractiles et le comportement des unités motrices lors de contractions lentes et très rapides (contractions balistiques). Cela nous a permis de vérifier s’il existait chez les seniors une relation entre la diminution de force, de sa vitesse d’installation, et la stratégie d’activation des unités motrices.

Enfin, dans l’étude V, nous avons analysé la fatigabilité neuromusculaire chez les seniors, comparativement aux sujets jeunes. Plus spécifiquement, nous avons étudié les contractions concentriques et excentriques maximales fatigantes. La fatigue n’a en effet pas encore été étudiée lors de ces deux types de contraction chez les adultes jeunes et âgés. L’objectif de cette dernière étude était surtout d’analyser la part relative des mécanismes nerveux et musculaires à l’origine de la fatigue ainsi que leur décours dans le temps en fonction de l’âge des sujets.

L’approche méthodologique utilisée nous a permis d’analyser les modifications fonctionnelles du muscle et de ses unités motrices avec l’âge. Un intérêt tout particulier a été porté aux ajustements de la commande nerveuse et à la compréhension des mécanismes sous-jacents. L’ensemble de nos résultats expérimentaux documentent de manière originale l’interaction étroite entre les adaptations nerveuses et musculaires au cours du vieillissement. Plus largement, notre travail doctoral contribue à une meilleure connaissance de la remarquable plasticité du système neuromusculaire chez l’homme.

Résumé en anglais :\
Doctorat en Sciences de la motricité
info:eu-repo/semantics/nonPublished

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Parra, Francisco Diaz. « Benefits of unit rate contracting in the petrochemical industry ». Online version, 2008. http://www.uwstout.edu/lib/thesis/2008/2008parrad.pdf.

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Schmid, Steven J. « Developing the best methods of internal contracting support for deployed Marine Expeditionary Units (MEU) ». Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA401602.

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Thesis (M.S. in Management) Naval Postgraduate School, Dec. 2001.
Thesis advisor(s): Cuskey, Jeffrey R.; Lamm, David V. "December 2001." Includes bibliographical references (p. 69-71). Also available in print.

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McKeown, Daniel. « The Effect of Hypoxia on the Neural Control of Muscle Contraction ». Thesis, Griffith University, 2022. http://hdl.handle.net/10072/415265.

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The availability of oxygen (O2) is vital for maintaining neurological function during exercise. This is clear when performing exercise in low oxygen environments, such as high altitude, where reductions in O2 availability result in limitations in motor performance. However, the ongoing contribution of central and peripheral mechanisms to hypoxia-related limitations in motor performance is yet to be fully understood. A wide variety of experimental designs have been used to test motor pathways during hypoxic exposure. Indeed, there is little consistency in the literature with regards to 1) the severity of hypoxic exposure, 2) the duration of hypoxic exposure, 3) the fatigue-state of the motor system, and 4) the intensity of exercise. This Thesis presents a series of controlled laboratory experiments which assess the effects of acute hypoxia (2 hr at 80% SpO2) on central and peripheral motor mechanisms. The experiments used high-density electromyography, electrical stimulation of the motor nerve (MNS), and transcranial magnetic stimulation (TMS) of the motor cortex, to clarify how motor activity is affected with hypoxia. The first experiment assessed how the firing characteristics of biceps brachii motor units (MU) were modulated by acute hypoxia when performing sustained isometric elbow flexions. Maximal voluntary contraction (MVC) toque remained unaffected during hypoxia, however, individuals exhibited specific changes in MU firing. Bidirectional changes in MU discharge were strongly correlated to the rate of desaturation and sensitivity to O2 availability during the titration phase. Differences in intrinsic properties of neurons, afferent input to motoneurones, neuromodulation, and sympathetic nerve activity may explain these differences. The second experiment assessed how corticospinal excitability, voluntary activation using motor nerve stimulation (VAMNS) and perception of fatigue (RPF) during brief and sustained MVCs were modulated by acute hypoxia. RPF and corticospinal excitability increased, while VAMNS decreased across the hypoxia protocol. Changes in the motor evoked potential (MEP) area and VAMNS were only seen during the brief MVCs and not the sustained MVCs. This may be due to redirection of blood flow to active areas of the motor system during prolonged contraction. The third experiment assessed how acute hypoxia altered neural mechanisms of muscle activation during, and following recovery from, a sustained submaximal (20% MVC) fatiguing contraction. MVC torque, root mean square EMG (EMGRMS), VAMNS and voluntary activation using TMS (VATMS), RPF, MEP area, and silent period duration (SP) were measured to characterise muscle activation. Hypoxia effects were only seen during the recovery phase, where VAMNS and VATMS, as well as MEP area, was reduced during acute hypoxia. This was likely due to hypoxia-related mechanisms involving supraspinal motor circuits that were impaired during the recovery phase. The fourth experiment assessed how acute hypoxia altered the neural mechanisms of muscle activation across a full range of force output once fatigued. MVC torque, EMGRMS, VAMNS and VATMS, MEP area, and SP were assessed following the sustained MVC. VATMS was reduced during hypoxia, which was not reflected in VAMNS. This indicates that acute hypoxia significantly impaired the ability of the motor cortex to voluntarily activate the fatigued muscle. This was partly due to suboptimal output from the motor cortex. Collectively, the findings of the four experiments in this Thesis provide novel evidence that a moderate acute hypoxic stimulus 1) reduces VA of a muscle during maximal and submaximal contraction due to suboptimal output from the motor cortex, 2) modulates the excitability of the corticospinal pathway, and 3) enhances perceptions of muscle fatigue during maximal, but not submaximal, fatiguing contractions. For these findings to occur, the elbow flexor muscle group needed to be sufficiently fatigued during at least 2 hr of prolonged exposure to a moderate hypoxic stimulus.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Health Sci & Soc Wrk
Griffith Health
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Trimble, Mark Herbert 1958. « EFFECTS OF ELECTRICAL STIMULATION ON THE RECRUITMENT ORDER OF MOTOR UNITS IN MAN : INDIRECT EXAMINATION BY ELECTRICALLY EVOKED MUSCLE RESPONSES ». Thesis, The University of Arizona, 1987. http://hdl.handle.net/10150/276555.

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Although the neural mechanisms responsible for the orderly recruitment of motor units have been investigated extensively, the flexibility of the underlying neural circuitry remains unclear. For example, the effects of electrical stimulation on the recruitment order of motor units is not well understood. This project was designed to study the recruitment order of motor units in man during different stimulation protocols. Examination of the compound-twitch characteristics of electrically evoked responses allowed an indirect determination of motor-unit recruitment order. The results demonstrate that the recruitment order of quadriceps femoris and triceps surae motor units differs according to the stimulation protocols used. Analysis of the compound-twitch characteristics indicated that the recruitment order of motor units during Hoffmann reflexes is similar to that of volitional muscle contractions but effectively the reverse of that during direct-motor responses. Moreover, the results suggest that cutaneous-afferent stimulation alters the recruitment thresholds of different motor unit types during the Hoffman reflex.

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Dean, Valarie Nichole. « Time Constant Analysis of Initial 'Jump' in Firing Rate of Human Motor Units During Isometic Contraction ». Thesis, The University of Arizona, 2010. http://hdl.handle.net/10150/146201.

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Ongoing research studying the underlying mechanism and prevalence of Persistent Inward Currents (PICs) has posed a challenge to the conventional view that the firing rate of a motor unit is proportional to the amount of synaptic input it receives. Near the time of human motor unit recruitment during isometric muscle contraction, a sudden steep rise in firing rate is observed, which is suggested to result from rapid triggering of PICs, an intrinsic property of motor neurons. In evaluating the time constants associated with these steep rises in firing rate across different contractile speeds, it has been found that the time course of the steep rise is dependent on the time course of muscle contraction. This evidence suggests that the mechanism underlying this steep rise in firing rate is not PIC-associated, but rather depends on an alternate, unknown mechanism.

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Perez, Diana. « Can humans fully activate the motor units of the quadriceps femoris muscle when performing a maximal voluntary contraction ? » Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=69743.

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The ability to fully activate the motor units of the quadriceps femoris muscle when performing an isometric maximal voluntary contraction (MVC) was assessed in 30 subjects. The twitch interpolation technique (TIT) was used to measure the increase in force superimposed on the MVC by a supramaximal shock to the femoral nerve. The superimposed force was compared to the potentiated twitch (PtP) force, and an activation ratio (A.R.) was calculated. The resting twitch (PtR) force, MVC force, and the inverse relationship between the level of voluntary force and the superimposed twitch force were also measured. Subjects were compared on the basis of activity level (15 sedentary and 15 trained) and gender (14 males and 16 females). The mean A.R. was 95% regardless of activity level or gender. Males were stronger than females but there was no difference in strength between the sedentary and trained groups. PtR and PtP force values showed the same pattern of results. The nature of the relationship between the level of voluntary force and the superimposed twitch force was curvilinear, and indicates that the TIT may not be accurate in measuring the amount of activation for a muscle as large as the quadriceps when voluntary contractions greater than 70% of the MVC are performed. The intra-subject reliability of the TIT used in this lab was acceptable (ICC = 0.78).

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Livres sur le sujet "Contractile units"

Iyer, Meenakshi Balkrishna. Firing behavior of human motor units during quasi-sinusoidal isometric muscle contractions. [New York] : Columbia University, 1993.

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Great Britain. Office of Public Service and Science. Efficiency Unit. Competing for quality policy review : An Efficiency Unit scrutiny. London : HMSO, 1996.

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Bragg, Steven M. Outsourcing : A guide to-- selecting the correct business unit-- negotiating the contract-- maintaining control of the process. New York : Wiley, 1998.

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Outsourcing : A guide to-- selecting the correct business unit-- negotiating the contract-- maintaining control of the process. 2^e éd. Hoboken, NJ : John Wiley, 2006.

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Washington (State). Dept. of Personnel. et Washington State Library. Electronic State Publications., dir. Employee business unit (EBU) : Fact sheet. [Olympia, Wash.] : Washington State Dept. of Personnel, 2005.

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Nick, Carter, Healthcare Financial Management Scheme et Chartered Institute of Public Finance and Accountancy., dir. Case mix analysis for contracting and pricing : A view from a unit financial director. London : Healthcare Financial Managment Association, 1991.

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Fink, William Michael. An assessment of the Navy's Productive Unit Resourcing (PUR) system in use at Navy Field Contracting Activities. Monterey, Calif : Naval Postgraduate School, 1988.

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Booth, Tim. Contracting arrangements in domiciliary care : A report of a national survey by the Joint Unit for Social Services Research. Sheffield : [JUSSR], 1990.

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Baker, James Mark. An assessment of incorporating quantified contract administration functions in use at Navy Field Contracting Activities into the Navy's Productive Unit Resource (PUR) system. Monterey, Calif : Naval Postgraduate School, 1989.

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Yang, Zhihong, et Xiu-Fen Ming. Adventitia and perivascular adipose tissue—the integral unit in vascular disease. Oxford University Press, 2017. http://dx.doi.org/10.1093/med/9780198755777.003.0020.

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Obesity and obesity-associated metabolic disorders are highly associated with cardiovascular disease. Abnormal ectopic deposition and accumulation of adipose tissue in organs, including perivascular space (perivascular adipose tissue, PVAT) in obesity are emerging to contribute to vascular disease development through pathological paracrine and/or endocrine secretion of cytokines, namely adipokines, which are vasoactive factors including vascular relaxing and contracting factors, smooth muscle growth promoting and inhibiting factors, and pro- and anti-inflammatory factors. In obesity, production of these factors from PVAT is altered and in imbalance which favours vascular contraction, pathological remodelling, and inflammation. In cross-talk with the endothelium, the functional changes of adventitia and PVAT are detrimental and importantly contribute to the acceleration of vascular atherosclerosis and complications associated with obesity and metabolic disorders

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Chapitres de livres sur le sujet "Contractile units"

Estrada-González, Luis, et Elisángela Ramírez-Cámara. « Non-conditional Contracting Connectives ». Dans Logic, Epistemology, and the Unity of Science, 349–64. Cham : Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-53654-1_12.

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Zerbini, Gianpaolo. « The Cell Membrane of the Contractile Unit ». Dans Cellular Physiology and Metabolism of Physical Exercise, 17–21. Milano : Springer Milan, 2012. http://dx.doi.org/10.1007/978-88-470-2418-2_3.

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Grimby, L. « The Use of Low and High Threshold Units During Voluntary Contraction and Locomotion ». Dans Motor Control, 13–17. Boston, MA : Springer US, 1987. http://dx.doi.org/10.1007/978-1-4615-7508-5_3.

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Frančič, A., et A. Holobar. « Motor Unit Tracking Across Low Contraction Levels of Biceps Brachii Muscle ». Dans Biosystems & ; Biorobotics, 401–5. Cham : Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-70316-5_64.

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Panolan, Fahad, Saket Saurabh et Meirav Zehavi. « Contraction Decomposition in Unit Disk Graphs and Algorithmic Applications in Parameterized Complexity ». Dans Proceedings of the Thirtieth Annual ACM-SIAM Symposium on Discrete Algorithms, 1035–54. Philadelphia, PA : Society for Industrial and Applied Mathematics, 2019. http://dx.doi.org/10.1137/1.9781611975482.64.

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Holobar, A., M. A. Minetto, A. Botter et D. Farina. « Identification of Motor Unit Discharge Patterns from High-Density Surface EMG during High Contraction Levels ». Dans IFMBE Proceedings, 1165–68. Berlin, Heidelberg : Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-23508-5_301.

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Kaczmarek, Piotr, et Andrzej Kasinski. « Estimation of a Muscle Force from a Mechanomyographic Signal During a Contraction of a Single Motor Unit ». Dans Advances in Soft Computing, 581–88. Berlin, Heidelberg : Springer Berlin Heidelberg, 2007. http://dx.doi.org/10.1007/978-3-540-75175-5_73.

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Shindo, Masaomi. « Modulation of Reciprocal Ia Inhibition from Pretibial Flexors to Extensors During Tonic Pretibial Contraction in Man : Analysis with Single Motor Unit Recording ». Dans Alpha and Gamma Motor Systems, 533–36. Boston, MA : Springer US, 1995. http://dx.doi.org/10.1007/978-1-4615-1935-5_116.

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Evans, Rhys, Kenneth T. MacLeod, Steven B. Marston, Nicholas J. Severs et Peter H. Sugden. « Cardiac physiology ». Dans Oxford Textbook of Medicine, 2618–27. Oxford University Press, 2010. http://dx.doi.org/10.1093/med/9780199204854.003.160103_update_002.

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The function of the heart is to provide the tissues of the body with sufficient oxygenated blood and metabolites to meet the moment-to-moment needs as dictated by physical activity and postural and emotional changes. Cardiac myocytes are the contractile cells of the heart and constitute the bulk of heart mass. There are differences between the myocytes of the ventricles, the atria, and the conduction system: ventricular myocytes are elongated cells, packed with myofibrils (the contractile apparatus) and mitochondria (for ATP production). Myofibrils are repeating units (sarcomeres) made up of thin actin filaments anchored at the Z-discs at either end of the sarcomere, and thick myosin filaments which interdigitate and interact with the thin filaments. Contraction results from sarcomere shortening produced by the ATP-dependent movement of the thin and thick filaments relative to one another. Transverse (T-) tubules facilitate extracellular Ca...

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« Histology of the Parotid Gland ». Dans Diagnostic Techniques and Therapeutic Strategies for Parotid Gland Disorders, 6–12. IGI Global, 2021. http://dx.doi.org/10.4018/978-1-7998-5603-0.ch002.

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This chapter describes the characteristic histological features of the parotid gland. The microanatomy of the parotid gland includes the following: stroma (connective tissue) and parenchyma (secretory units or acini, myoepithelial cells, and ductal units). The secretory cells are organized into secretory units or acini, which are lined exclusively by serous cells. Myoepithelial cells are the contractile elements with secretory end pieces and intercalated ducts. The acini are drained by a series of ducts which eventually drain into the major excretory duct (Stensen's duct). Aging of salivary glands show some structural changes, but with no overall change in the amount of saliva secreted with advancing age.

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Actes de conférences sur le sujet "Contractile units"

Dixon, J. Brandon. « Engineering Tools for Studying the Interplay Between Mechanics and Biology in Lymphatic Lipid Transport ». Dans ASME 2010 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2010. http://dx.doi.org/10.1115/sbc2010-19364.

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The lymphatic vasculature extends through most tissues of the body and plays an essential role in maintaining fluid balance, immune cell trafficking, and lipid transport. Nearly all dietary lipid is transported from the intestine to the circulation via the lymphatic system in the form of triglyceride-rich lipoproteins called chylomicrons. This process can be described through two different mechanisms: 1) entry of the chylomicron into the initial lymphatic vessels of the small intestine, known as lacteals, and 2) the transport of these chylomicrons through the larger collecting lymphatics by a complex and coordinated system of individual contracting vessel units (lymphangions) and valve leaflets. We describe here a set of in vitro and in vivo tools we have developed to study the mechanisms that modulate lipid transport under these two different paradigms and show how these tools are uncovering important biological features involved in these mechanisms. Lymphatic pump function is known to be sensitive to the mechanical load on the vessel as the contractility of isolated vessels has been shown to be both shear and stretch sensitive [1], yet whether these mechanisms are important in regulating contractile function in vivo remains uncertain.

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Zhang, Xu, et Yi Zhao. « Selective Electrical Stimulation of Adult Cardiomyocyte for Studying Intercellular Mechanical Transmission ». Dans ASME 2013 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/sbc2013-14753.

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Heart diseases rank the top among the leading causes of death in the United States, and account for nearly 40% of all deaths 1. As the most important component of heart muscle, cardiac myocytes are the basic units to generate contractile forces and regulate heart function. There are extensive molecular and electrophysiological studies suggesting that the defective intercellular communication in cardiac myocytes is an underlying cause of left ventricular dysfunction in several heart diseases 2,3. However, there are limited evidences in terms of mechanical contractility and electromechanical transmission, which are the direct measures of intercellular communication in myocardium. This is largely due to the lack of appropriate tools that can quantitatively assess the mechanical performance of adult cardiac myocytes. In this study, a microengineered device is developed for quantitative assessment of cardiac mechanical performance in isolated adult myocytes. This device is capable of applying electrical stimulation to selected cardiac myocytes, measuring mechanical force generation in single cells, and examining intercellular mechanical transmission in longitudinally connected doublets of adult cardiac myocytes.

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Wanner, M. C., K. Baumeister, G. W. Kohler et H. Walze. « Application of Programmable Handling-Units in Contracting Companies ». Dans 2nd International Symposium on Automation and Robotics in Construction. International Association for Automation and Robotics in Construction (IAARC), 1985. http://dx.doi.org/10.22260/isarc1985/0004.

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Labazanova, Luiza, Zeyu Wu, Zhengping Gu et David Navarro-Alarcon. « Bio-Inspired Design of Artificial Striated Muscles Composed of Sarcomere-Like Contraction Units ». Dans 2021 20th International Conference on Advanced Robotics (ICAR). IEEE, 2021. http://dx.doi.org/10.1109/icar53236.2021.9659330.

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Li, Yali, et N. C. Goulbourne. « Electro-Chemo-Mechanical Modeling of the Artery Myogenic Transient and Steady-State Response ». Dans ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-39237.

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Active contraction of smooth muscle results in the myogenic response and vasomotion of arteries, which adjusts the blood flow and nutrient supply of the organism. It is a multiphysic process coupled electrical and chemical kinetics with mechanical behavior of the smooth muscle. This paper presents a new constitutive model for the media layer of the artery wall to describe the myogenic response of artery wall for different transmural pressures. The model includes two major components: electrobiochemical, and chemomechanical parts. The electrochemical model is a lumped Hodgkin-Huxley-type cell membrane model for the nanoscopic ionic currents: calcium, sodium, and potassium. The calculated calcium concentration serves as input for the chemomechanical portion of the model; its molecular binding and the reactions with other enzyme cause the relative sliding of thin and thick filaments of the contractile unit. In the chemomechanical model, a new nonlinear viscoelastic model is proposed using a continuum mechanics approach to describe the time varying behavior of the smooth muscle. Specifically, this model captures the filament overlap effect, active stress evolution, initial velocity, and elastic recoil in the media layer. The artery wall is considered as a thin-walled cylindrical tube. Using the proposed constitutive model and the thin-walled equilibrium equation, the myogenic response is calculated for different transmural pressures. The integrated model is able to capture the pressure-diameter transient and steady-state relationship.

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Naisse, Jean-Claude. « Lessons Learnt From Ignalina NPP Decommissioning Project ». Dans The 11th International Conference on Environmental Remediation and Radioactive Waste Management. ASMEDC, 2007. http://dx.doi.org/10.1115/icem2007-7351.

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The Ignalina Nuclear Power Plant (INPP) is located in Lithuania, 130 km north of Vilnius, and consists of two 1500 MWe RBMK type units, commissioned respectively in December 1983 and August 1987. On the 1st of May 2004, the Republic of Lithuania became a member of the European Union. With the protocol on the Ignalina Nuclear Power in Lithuania which is annexed to the Accession Treaty, the Contracting Parties have agreed: - On Lithuanian side, to commit closure of unit 1 of INPP before 2005 and of Unit 2 by 31 December 2009; - On European Union side, to provide adequate additional Community assistance to the efforts of Lithuania to decommission INPP. The paper is divided in two parts. The first part describes how, starting from this agreement, the project was launched and organized, what is its present status and which activities are planned to reach the final ambitious objective of a green field. To give a global picture, the content of the different projects that were defined and the licensing process will also be presented. In the second part, the paper will focus on the lessons learnt. It will explain the difficulties encountered to define the decommissioning strategy, considering both immediate or differed dismantling options and why the first option was finally selected. The paper will mention other challenges and problems that the different actors of the project faced and how they were managed and solved. The paper will be written by representatives of the Ignalina NPP and of the Project Management Unit.

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Ibrahim, Mohamed Walid A., et Syed Ali Yousaf. « Proven Effective Contracting Strategy to Enhance Brownfield Capital Projects Execution ». Dans ADIPEC. SPE, 2022. http://dx.doi.org/10.2118/210889-ms.

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Abstract Long Term Agreement (LTA) contracting strategy is a new developed strategy for capital projects that has holistic objective of not only eliminating the Cons of traditional heavily implemented contracting strategies; Lump Sum TurnKey (LSTK) and Lump Sum Procure and Build (LSPB) but more importantly to increase the domestic dependency on manpower and manufacturing. LTA is a hybrid strategy between LSTK and Work Unit Rate/ Time Unit Rate (WUR/TUR). For a fixed period of time and specific work zone, contractor is granted LSTK contracts for an agreed upon WUR. In this paper, the development of this new strategy will be discussed, its Pros and what advantages it achieved after implementation. Existing processing facilities consistently need upgrades that is business driven hence, need to be executed on an expedited mode while the projects budgets are relatively low (less than $100 million US dollars). These projects need to be executed while the existing facility is on stream, producing and within a specific schedule and pre-determined aggressive milestones. Hence, the implementation of LTA contracting strategy for oil and gas capital projects in brown fields can reduce contracting phase period by up to 70 %. This paper research work is focused on the implementation of LTA contracting strategy in brown field projects specifically in gas processing facilities construction projects with budget less than $100 milion US dollars/ project department. The evaluation compares the current recommended LSTK contracting strategy verses LTA contracting strategy proposed. The two strategies are assessed on the bases of time efficiency and effectiveness of cost control during the project execution life cycle. The comparison was done on realistic time utilizing decision tools analysis approach. The time frames are extracted from processes mandated by "Company" Engineering procedures "SAEP". The two awarding strategies are furthered analyzed using lean tools and methods. Furthermore, a comparison between the three contracting strategies; LSTK, LSPB, and LTA is conducted. In 2019, the author has published a paper with the same comparison between LSTK and LSPB for capital projects with budgets $100 million US dollars or less under specific conditions. Four (4) sets of assessments were conducted with one variable effect is assessed at a time and the remaining are finalized in order to develop recommendation for which contracting strategy to be used when. In the current paper, the author(s) chose to conduct a similar assessment with minor modifications on the conditions but with the introduction of the LTA as a third contracting option. New set of recommendations are developed and graph distribution will be displayed. It can be shown that the newly introduced contracting strategy LTA has significant advantages and positive impact on both the company and stockholders. For instance, it will improve the Overall performance of Oil & Gas (O&G) brownfield upgrade projects execution to align with Industry Benchmark through the following focused benefits; improving the contracting cycle time by 70% hence optimizing the procurement cycle. It will allow contractors to allocate dedicated construction resources which will create a strong potential for cost and schedule optimization and effective planning/execution for bottleneck activities like Tie-ins and shutdown related scope. Availability of high-quality skilled manpower will most definitely improve job site quality and safety related issues. In addition, a demand on local manufacturing industry will increase. Therefore, there will be an increase in the Local jobs offering and strong support for the government In Kingdom Total Value-Added program (IKTVA) aimed at development and retaining of local manpower and Saudi resources.

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Oda, Keita, Takahiro Ishihara et Masakatsu Miyajima. « Pipeline Design Method Against Large Displacement of Strike-Slip Fault ». Dans ASME 2016 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/pvp2016-63699.

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This study proposes a method for designing a water pipeline system against fault displacement by incorporating earthquake resistant ductile iron pipes (ERDIPs). An ERDIP pipeline is capable of absorb the large ground displacements that occur during severe earthquakes by movement of its joint (expansion, contraction and deflection) and the use of the joint locking system. Existing ERDIP pipelines have been exposed to several severe earthquakes such as the 1995 Kobe Earthquake and the 2011 Great East Japan Earthquake, and there has been no documentation of their failure in the last 40 years. In the case of a pipeline that crosses a fault, there is the possibility of the occurrence of a local relative displacement between the pipeline and the ground. It is known that an ERDIP pipeline withstands a fault of axial compression direction by past our study. Hence, this present study was targeted at developing a method for designing an ERDIP pipeline that is capable of withstanding a strike-slip fault of axial tensile direction for a pipeline. This was done by FEM analysis wherein the ERDIPs and spring elements were used to model the soil and ERDIP joints. An ERDIP pipeline can accommodate a fault displacement of about 2 m by joint expansion/contraction and deflection, while maintaining the stress in the pipeline within the elastic limit. However, additional countermeasure is required when the fault displacement exceeds 2 m because such could stress the pipeline beyond the elastic limit. The use of large displacement absorption unit is an effective countermeasure for displacements exceeding 2 m. The expansion/contraction capacity of a unit is 10 times that of an ERDIP joint and it is able to absorb a locally-concentrated axial displacement of the pipeline. It was confirmed in the present study that an ERDIP pipeline with large displacement absorption unit, referred to as a large displacement absorption system, could accommodate fault displacement in excess of 2 m within the elastic stress range of the pipeline.

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Broughton, Ronnie T. « Low Pressure Injection System Crossconnect Modification ». Dans ASME 2005 Power Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/pwr2005-50075.

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How would you fix all of the Low Pressure Injection (LPI) system technical problems listed below with a single nuclear plant modification? • Large LPI Flow indication uncertainty; • Non-Safety power to important cross connect valves; • LPI Pump run-out / NPSH operator burden; • Unbalanced LPI cooling due to electrical single failure; • Unconventional response to valve single failure. A southeastern nuclear generation facility responded by contracting Framatome ANP to design a new passive single cross connect modification for each of their generating units. This new cross connect, consisting of approximately 130’ of 10” stainless steel piping, new gate valves, new check valves, and two new flow restrictors, was installed downstream of the LPI coolers and inside containment on each unit to tie the two injection trains together. The two flow restrictors (stemless globe valves with precision engineered disc stacks) were the centerpiece of the design. Though system resistance is increased, the flow restrictors eliminate all of the technical issues that the utility faced in the LPI system. The passive nature of this design eliminated the time-critical operator burden, the need for safety grade power on existing cross connect valves, the threat of pump run-out and marginal NSPHa, and the unusual single failure licensing basis to manually open LPI isolation valves in the event that they failed closed. The design also improved flow indication uncertainty with a change out of the existing flow measuring orifices. Framatome ANP faced many challenges during the design process. In addition to the problems to be solved, other constraints of the modification were significant, including: an unusually tight upper limit on pump strength, a narrow band of acceptable system resistance with an unknown baseline, first-of-a-kind accuracy requirements for the flow restrictor, and High Pressure Injection (HPI) system minimum flow limits challenged by modification operational changes. The NRC has approved the flow restrictor and the overall design for use in this facility. The passive cross connect modification has been installed in all units. All equipment has passed installation and post modification testing requirements.

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Zhang, Chi, et Yingxin Gao. « A 2D Finite Element Model of Lateral Transmission of Force in Skeletal Muscle ». Dans ASME 2011 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2011. http://dx.doi.org/10.1115/sbc2011-53353.

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Skeletal muscle has a complex hierarchical structure which is mainly composed of myofibers and the surrounding extracellular matrix (ECM) including endomysium, perimysium, and epimysium. Myofibers are long, cylindrical, multinucleated cells composed of repeating sarcomeres, which are basic functional units for skeletal muscle contraction. In order to produce body movement, the force generated by myofiber has to be transmitted from individual fiber to the tendon. The commonly accepted site for force transmission is the myotendinous junction (MTJ) where the myofibers connect to the tendon. However, the myofibers mainly end within the muscle fascicles without reaching the MTJ in many muscles, in which case the force has to be transmitted laterally to adjacent fiber through shear and to the tendon eventually.

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Rapports d'organisations sur le sujet "Contractile units"

Pendergast, Clinton R. Non-Acquisition Unit Responsibilities for Contingency Contracting. Fort Belvoir, VA : Defense Technical Information Center, avril 2012. http://dx.doi.org/10.21236/ada563397.

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Torres, Isaac, et Marvin L. Ross. How Can We Best Achieve Contracting Unity of Effort in the CENTCOM Area of Responsibility ? Fort Belvoir, VA : Defense Technical Information Center, novembre 2013. http://dx.doi.org/10.21236/ada613002.

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Torres, Isaac, et Marvin Ross. How Can We Best Achieve Contracting Unity of Effort in the CENTCOM Area of Responsibility ? Fort Belvoir, VA : Defense Technical Information Center, décembre 2013. http://dx.doi.org/10.21236/ada620490.

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