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Skeletal Muscle
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
A thick filament is 10–12 nm in diameter, about 1.6 µm long, and consists of some 300 molecules of a type of myosin. This myosin molecule is about 150 nm long, has a molecular weight of about 480 kdaltons, a globular head composed of two subunits, a long tail, and an intermediate neck region that allows the head some flexibility (Figure 9.4a). The molecule resembles two golf clubs having their long handles twisted together. The molecules are oriented with their tails pointing toward the M line, and with the long tail of a myosin molecule bound to the tails of other myosin molecules to form a thick filament. The globular heads of the myosin molecules protrude from the body of the thick filament, successive heads being displaced about 14 nm longitudinally and rotated 60° around the filament, in accordance with the hexagonal arrangement in Figure 9.3. The orientation of the myosin molecules, and their shape, leaves about 100 nm of the thick filament, on either side of the M line, devoid of any heads, which makes this region somewhat lighter than the rest of the A band.
Optimizing 3D Models of Engineered Skeletal Muscle
Published in Karen J.L. Burg, Didier Dréau, Timothy Burg, Engineering 3D Tissue Test Systems, 2017
Megan E. Kondash, Brittany N. J. Davis, George A. Truskey
Mature skeletal muscle consists of four primary mature fiber types distinguished by the primary expressed form of myosin heavy chain; type 1 fibers, which are characterized by slow twitch kinetics and the presence of oxidative enzymes, and three forms of type 2 fibers characterized by fast twitch kinetics and the presence of more glycolytic enzymes. Fast twitch fibers express higher levels of GLUT1 and lower levels of GLUT4 than their slow twitch counterparts (Daugaard et al. 2000; Gaster et al. 2000). Interestingly, skeletal muscle cultured in vitro had a much higher percentage of fast twitch fibers, as identified by expression of fast twitch associated myosin heavy chain proteins, than the tissue from which it was isolated (Gaster et al. 2001), and cultured myotubes typically express more immature embryonic and perinatal myosin heavy chain isoforms (Cheng et al. 2014). If myotubes in vitro have a tendency to differentiate into fast twitch fibers, this may partially explain the lower expression levels of GLUT4 than their counterpart muscle in vivo.
Innovative and Advanced Motor Design
Published in Wei Tong, Mechanical Design and Manufacturing of Electric Motors, 2022
Molecular machines convert chemical, electrical, or other forms of energy into mechanical work for unidirectional movement. As an important component among them, molecular motors refer to the motors in molecular scales. Although molecular motors may overlap with nanomotors in their size, molecular motors often refer to the motors with a single molecule. They are of great interest not only for their basic scientific richness, but also for the potential to revolutionize critical technologies. In fact, molecular motors exist in nature, for example, in the form of myosins. Myosins are motor proteins that play an important role in living organisms in the contraction of muscles and the transport of other molecules between cells [15.70].
Energetics of molecular motor proteins: could it pay to take a free ride?
Published in Molecular Physics, 2018
Molecular motor proteins are widely used in biological systems to generate directional motion [1]. They are used to generate actual bodily motion, such as muscle contraction, and in cells to move material from one place to another. Here, we are interested in the latter. Directed transport occurs by motor proteins binding to sites on certain semi-stiff ‘track’ filaments that are assemblies of globular proteins with a polarity. They then process in a given direction, determined by the polarity of the track. The exact mechanism by which this occurs is still a matter of debate. However, the consensus is that the motors hydrolyse ATP and undergo a configurational change that moves them along to the next binding site [2,3]. Motor proteins primarily differ in the track to which they bind and in which direction they move once bound to the track. Myosin binds to actin filaments and provides the driving force for muscle contraction. The motors proteins kinesin and dynein bind to microtubules. Once bound to the track, the former heads towards the positive end of the track and the latter towards the negative end. The end of the protein that does not bind to the track binds to ‘cargoes’, such as proteins and vesicles. Once attached, the motor with loaded cargo transports it along the track. As such, this is the mechanism behind most active transport of proteins and vesicles in the cytoplasm. On the scale of a typical cell, this transport takes place over distances in the order of microns. Directed motion over much longer scales occurs in cells such as axons (a giraffe has an axon [4] that is 2m in length, vying with the giant squid [5] for the record), where it is believed to be linked to various neural dysfunctions including Alzheimer's disease [6].
Modelling and simulation of sprinters’ health promotion strategy based on sports biomechanics
Published in Connection Science, 2021
Wang Huifeng, Achyut Shankar, G.N. Vivekananda
As the knee flexes deeper, the natural knee femoral posterior roll increases, accompanied by the internal rotation of the tibia. The knee joint is forced or twisted by the flexion position, and the tension of the iliac crest is increased, and the tibial articular surface is displaced, twisted, impacted and rubbed. If the long-term load of these forces exceeds the physiological limit of cartilage and hinders the normal metabolism, it will lead to changes in articular cartilage, which will lead to a series of pathological changes such as fibrosis, calcification and chondrocyte swelling. If the action is wrong, contrary to the human anatomy and the dynamic biomechanical law, it will cause anti-joint activity, the muscle is in a “passively insufficient” state, and the ligament is excessively pulled, resulting in a sprain or strain. All kinds of human movements are accomplished by the contraction of muscle cells. From the molecular level, the contraction of various muscles is related to the contraction ability of contractile proteins in muscle cells, that is, the interaction ability between myosin and myofibrin. Muscle contraction results from a communication between the myosin and actin filaments that generates movement relative to one another. On the molecular basis, interaction is the binding of myosin to actin filaments and it allows myosin to function as a motor that drives the filament sliding. Myofibril is a functional unit of skeletal muscle and it composed of syncytia of multinucleated cells that differ considerably in their physiological and biochemical properties. Therefore, in the support stage, in order to reduce the loss of the horizontal speed of the body's centre of gravity and bring greater acceleration effect to the centre of gravity, we emphasise that fast leg swing and hip extension are very meaningful, they are effective means to improve the speed of running. When the knee joint is moving at different positions and speeds, the activity of each muscle has important guiding significance for the evaluation of muscle strength test results and the formulation of specific strength training plans.