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Handbook of Clinical Neurology 2023Contractions of skeletal muscles provide the stability and power for all body movements. Consequently, any impairment in skeletal muscle function results in some degree... (Review)
Review
Contractions of skeletal muscles provide the stability and power for all body movements. Consequently, any impairment in skeletal muscle function results in some degree of instability or immobility. Factors that influence skeletal muscle structure and function are therefore of great interest scientifically and clinically. Injury, neuromuscular disease, and old age are among the factors that commonly contribute to impairments in skeletal muscle function. The goal of this chapter is to summarize the fundamentals of skeletal muscle structure and function to provide foundational knowledge for this Handbook volume. We examine the molecular interactions that provide the basis for the generation of force and movement, discuss mechanisms of the regulation of contraction at the level of myofibers, and introduce concepts of the activation and control of muscle function in vivo. Where appropriate, the chapter updates the emerging science that will increase understanding of muscle function.
Topics: Humans; Muscle Contraction; Muscle, Skeletal; Muscular Diseases
PubMed: 37562874
DOI: 10.1016/B978-0-323-98818-6.00013-3 -
The Journal of General Physiology Sep 2022
Topics: Calcium; Excitation Contraction Coupling; Heart; Muscle Contraction; Muscle, Skeletal; Muscle, Smooth
PubMed: 35984377
DOI: 10.1085/jgp.202213244 -
International Journal of Molecular... Feb 2023The "motor unit" or the "muscle" has long been considered the quantal element in the control of movement. However, in recent years new research has proved the strong... (Review)
Review
The "motor unit" or the "muscle" has long been considered the quantal element in the control of movement. However, in recent years new research has proved the strong interaction between muscle fibers and intramuscular connective tissue, and between muscles and fasciae, suggesting that the muscles can no longer be considered the only elements that organize movement. In addition, innervation and vascularization of muscle is strongly connected with intramuscular connective tissue. This awareness induced Luigi Stecco, in 2002, to create a new term, the "myofascial unit", to describe the bilateral dependent relationship, both anatomical and functional, that occurs between fascia, muscle and accessory elements. The aim of this narrative review is to understand the scientific support for this new term, and whether it is actually correct to consider the myofascial unit the physiological basic element for peripheral motor control.
Topics: Muscle, Skeletal; Fascia; Connective Tissue; Muscle Fibers, Skeletal; Muscle Contraction
PubMed: 36901958
DOI: 10.3390/ijms24054527 -
Physiology (Bethesda, Md.) Nov 2019Muscle contraction is a three-dimensional process, as anyone who has observed a bulging muscle knows. Recent studies suggest that the three-dimensional nature of muscle... (Review)
Review
Muscle contraction is a three-dimensional process, as anyone who has observed a bulging muscle knows. Recent studies suggest that the three-dimensional nature of muscle contraction influences its mechanical output. Shape changes and radial forces appear to be important across scales of organization. Muscle architectural gearing is an emerging example of this process.
Topics: Animals; Biomechanical Phenomena; Humans; Muscle Contraction; Muscle, Skeletal
PubMed: 31577172
DOI: 10.1152/physiol.00023.2019 -
Acta Physiologica (Oxford, England) May 2022
Topics: Mitochondria, Muscle; Muscle Contraction; Organelle Biogenesis
PubMed: 35305290
DOI: 10.1111/apha.13813 -
Annual International Conference of the... Jul 2022Smooth muscle is found extensively in the human body, including in blood vessels, airways, the gastrointestinal tract, and the urinary bladder. Although the contractile...
Smooth muscle is found extensively in the human body, including in blood vessels, airways, the gastrointestinal tract, and the urinary bladder. Although the contractile proteins of smooth muscle are very similar to those of striated muscle, smooth muscle's contractile mechanism has not been studied as extensively as those for cardiac and skeletal muscle. Previous studies developed a lumped model of muscle contraction and applied it to cardiac muscle and to skeletal muscle. In this study, this model is used to quantitatively describe the contractile properties of canine smooth muscle, using data from the literature. Results show that a single equation relating muscle force to muscle length and time, and a single set of model parameters, is able to describe smooth muscle's passive and active isometric forces, isometric twitch contractions, isotonic contractions, and an inverse force-velocity relation. The latter arises from the model without assumption of a particular force-velocity curve embodied as a contractile element. This new constitutive relation may be used to describe smooth muscle within larger physiological models, for instance to describe blood vessel constriction or urinary bladder function.
Topics: Animals; Dogs; Humans; Isometric Contraction; Muscle Contraction; Muscle, Skeletal; Muscle, Smooth; Urinary Bladder
PubMed: 36086339
DOI: 10.1109/EMBC48229.2022.9871599 -
Trends in Biochemical Sciences Nov 2023The ability of skeletal muscle to adapt to repeated contractile stimuli is one of the most intriguing aspects of physiology. The molecular bases underpinning these... (Review)
Review
The ability of skeletal muscle to adapt to repeated contractile stimuli is one of the most intriguing aspects of physiology. The molecular bases underpinning these adaptations involve increased protein activity and/or expression, mediated by an array of pre- and post-transcriptional processes, as well as translational and post-translational control. A longstanding dogma assumes a direct relationship between exercise-induced increases in mRNA levels and subsequent changes in the abundance of the proteins they encode. Drawing on the results of recent studies, we dissect and question the common assumption of a direct relationship between changes in the skeletal muscle transcriptome and proteome induced by repeated muscle contractions (e.g., exercise).
Topics: Muscle, Skeletal; Exercise; Transcriptome; Muscle Contraction; Proteome
PubMed: 37709636
DOI: 10.1016/j.tibs.2023.08.005 -
Clinical Neurophysiology : Official... Sep 2022
Topics: Humans; Motor Neurons; Muscle Contraction
PubMed: 35817665
DOI: 10.1016/j.clinph.2022.06.011 -
Journal of Applied Physiology... Apr 2024Whether eccentric exercise involves active fascicle stretch is unclear due to muscle-tendon unit (MTU) series compliance. Therefore, this study investigated the impact...
Whether eccentric exercise involves active fascicle stretch is unclear due to muscle-tendon unit (MTU) series compliance. Therefore, this study investigated the impact of changing the activation timing and level (i.e., preactivation) of the contraction on muscle fascicle kinematics and kinetics of the human tibialis anterior during dynamometer-controlled maximal voluntary MTU-stretch-hold contractions. B-mode ultrasound and surface electromyography were used to assess muscle fascicle kinematics and muscle activity levels, respectively. Although joint kinematics were similar among MTU-stretch-hold contractions (∼40° rotation amplitude), increasing preactivation increased fascicle shortening and stretch amplitudes (9.9-23.2 mm, ≤ 0.015). This led to increasing positive and negative fascicle work with increasing preactivation. Despite significantly different fascicle kinematics, similar peak fascicle forces during stretch occurred at similar fascicle lengths and joint angles regardless of preactivation. Similarly, residual force enhancement (rFE) following MTU stretch was not significantly affected (6.5-7.6%, = 0.559) by preactivation, but rFE was strongly correlated with peak fascicle force during stretch ( = 0.62, = 0.003). These findings highlight that apparent eccentric exercise causes shortening-stretch contractions at the fascicle level rather than isolated eccentric contractions. The constant rFE despite different fascicle kinematics and kinetics suggests that a passive element was engaged at a common muscle length among conditions (e.g., optimal fascicle length). Although it remains unclear whether different fascicle mechanics trigger different adaptations to eccentric exercise, this study emphasizes the need to consider MTU series compliance to better understand the mechanical drivers of adaptation to exercise. Apparent eccentric exercises do not result in isolated eccentric contractions, but shortening-stretch contractions at the fascicle level. The amount of fascicle shortening and stretch depends on the preactivation during the exercise and cannot be estimated from the muscle-tendon unit (MTU) or joint kinematics. As different fascicle mechanics might trigger different adaptations to eccentric exercise, muscle-tendon unit series compliance and muscle preactivation need to be considered when eccentric exercise protocols are designed.
Topics: Humans; Muscle, Skeletal; Tendons; Muscle Contraction; Electromyography; Exercise; Isometric Contraction
PubMed: 38482578
DOI: 10.1152/japplphysiol.00845.2023 -
Biochemical Pharmacology Feb 2024Extracellular nucleotides and nucleosides are crucial signalling molecules, eliciting diverse biological responses in almost all organs and tissues. These molecules... (Review)
Review
Extracellular nucleotides and nucleosides are crucial signalling molecules, eliciting diverse biological responses in almost all organs and tissues. These molecules exert their effects by activating specific nucleotide receptors, which are finely regulated by ectonucleotidases that break down their ligands. In this comprehensive review, we aim to elucidate the relevance of extracellular nucleotides as signalling molecules in the context of smooth muscle contraction, considering the modulatory influence of ectonucleotidases on this intricate process. Specifically, we provide a detailed examination of the involvement of extracellular nucleotides in the contraction of non-vascular smooth muscles, including those found in the urinary bladder, the airways, the reproductive system, and the gastrointestinal tract. Furthermore, we present a broader overview of the role of extracellular nucleotides in vascular smooth muscle contraction.
Topics: Nucleotides; Muscle Contraction; Urinary Bladder; Nucleosides; Signal Transduction
PubMed: 38142836
DOI: 10.1016/j.bcp.2023.116005