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Myofibrils sarcomere

Figure 14.10 A muscle viewed under the microscope is seen to contain many myofibrils that show a cross-striated appearance of alternating light and darkbands, arranged in repeating units called sarcomeres. The dark bands comprise myosin filaments and are interupted by M (middle) lines, which link adjacent myosin filaments to each other. Figure 14.10 A muscle viewed under the microscope is seen to contain many myofibrils that show a cross-striated appearance of alternating light and darkbands, arranged in repeating units called sarcomeres. The dark bands comprise myosin filaments and are interupted by M (middle) lines, which link adjacent myosin filaments to each other.
FIGURE 17.12 Electron micrograph of a skeletal muscle myofibril (in longitndinal section). The length of one sarcomere is indicated, as are the A and I bands, the H zone, the M disk, and the Z lines. Cross-sections from the H zone show a hexagonal array of thick filaments, whereas the I band cross-section shows a hexagonal array of thin filaments. (Photo courtesy of Hugh Huxley, Brandeis University)... [Pg.542]

FIGURE 17.21 A drawing of the arrangement of the elastic protein titin in the skeletal mnscle sarcomere. Titin filaments originate at the periphery of the M band and extend along the myosin filaments to the Z lines. These titin filaments produce the passive tension existing in myofibrils that have been stretched so that the thick and thin filaments no longer overlap and cannot interact. (Adapted from Ohtsuki, ., Maruyama, K, and Ebashi,. S ., 1986. Advances ia Protein Chemisti y 38 1—67.)... [Pg.550]

Muscle contraction is initiated by a signal from a motor nerve. This triggers an action potential, which is propagated along the muscle plasma membrane to the T-tubule system and the sarcotubular reticulum, where a sudden large electrically excited release of Ca " into the cytosol occurs. Accessory proteins closely associated with actin (troponins T, I, and C) together with tropomyosin mediate the Ca -dependent motor command within the sarcomere. Other accessory proteins (titin, nebulin, myomesin, etc.) serve to provide the myofibril with both stability... [Pg.32]

Figure 1. Muscle development. A skeletal muscle fiber is formed by the fusion of many single cells (myoblasts) into a multinucleated myotube. Myotubes then develop into the muscle fiber (see text). Sarcomeres form in longitudinal structures called myofibrils. The repeating structure of the sarcomere contains interdigitating thick and thin filaments. Figure 1. Muscle development. A skeletal muscle fiber is formed by the fusion of many single cells (myoblasts) into a multinucleated myotube. Myotubes then develop into the muscle fiber (see text). Sarcomeres form in longitudinal structures called myofibrils. The repeating structure of the sarcomere contains interdigitating thick and thin filaments.
The muscle is composed of subunits called fascicles. The entire muscle and subunits with several fascicles are often surrounded by layers of connective tissue or fatty tissue. Fascicles are bundles of individual muscle fibres. Each fibre is one elongated cell that may extend for the length of the muscle. Each muscle fibre cell is segmented into distinct sectional bands. In contrast to most other tissues, cells of skeletal musculature have several nuclei. Within each muscle cell are numerous myofibrils, which also extend for the length of the muscle cell. Sarcomeres are the basic contractile subunit of myofibrils. [Pg.5]

Fig. 2. Macroscopic and microscopic structure of muscle (a) Entire muscle and its cross-section with fatty septa, (b) Fascicle with several muscle fibres (cells). A layer of fat along the fascicle is indicated, (c) Striated myofibre corresponding with one single muscle cell containing several nuclei. The lengths of a myofibre can be several tens of centimetres, (d) Myofibril inside a myocyte. It is one contractile element and contains actin and myosin and further proteins important for the muscular function, (e) Electron myograph of human skeletal muscle showing the band structure caused by the contractile myofilaments in the sarcomeres. One nucleus (Nu) and small glycogen granules (arrow, size <0.1 pm) are indicated. Fig. 2. Macroscopic and microscopic structure of muscle (a) Entire muscle and its cross-section with fatty septa, (b) Fascicle with several muscle fibres (cells). A layer of fat along the fascicle is indicated, (c) Striated myofibre corresponding with one single muscle cell containing several nuclei. The lengths of a myofibre can be several tens of centimetres, (d) Myofibril inside a myocyte. It is one contractile element and contains actin and myosin and further proteins important for the muscular function, (e) Electron myograph of human skeletal muscle showing the band structure caused by the contractile myofilaments in the sarcomeres. One nucleus (Nu) and small glycogen granules (arrow, size <0.1 pm) are indicated.
Figure 1.12 Diagrammatic interpretation of contraction in a myo-fibril of skeletal muscle. The diagram shows a single sarcomere, the basic contractile unit, limited at each end by a Z-disc. Muscle fibres are packed with hundreds of parallel myofibrils, each of which consists of many, often thousands, of sarcomeres arranged end to end. Contraction is the conseguence of the thin actin filaments being pulled over the thick filaments to increase the region of overlap and telescope the sarcomere. Figure 1.12 Diagrammatic interpretation of contraction in a myo-fibril of skeletal muscle. The diagram shows a single sarcomere, the basic contractile unit, limited at each end by a Z-disc. Muscle fibres are packed with hundreds of parallel myofibrils, each of which consists of many, often thousands, of sarcomeres arranged end to end. Contraction is the conseguence of the thin actin filaments being pulled over the thick filaments to increase the region of overlap and telescope the sarcomere.
Each fibre contains an array of parallel myofibrils each consisting of overlapping thick and thin filaments that form repeating units (sarcomeres) along the length of the fibre (Figure 13.5). The thick filaments are composed almost entirely of the protein myosin, whereas the thin filaments contain actin as well as troponin and tropomyosin. [Pg.279]

Figure 13.5 Electron micrograph of part of a longitudinal section of a myofibril. Identification of components and the mechanism of contraction. When a muscle fibre is stimulated to contract, the actin and myosin filaments react by sliding past each other but with no change in length of either myofilament. The thick myosin strands in the A band are relatively stationary, whereas the thin actin filaments, which are attached to the Z discs, extend further into the A band and may eventually obliterate the H band. Because the thin filaments are attached to Z discs, the discs are drawn toward each other, so that the sarcomeres, the distance between the adjacent Z-discs, are compressed, the myofibril is shortened, and contraction of the muscle occurs. Contraction, therefore, is not due to a shortening of either the actin or the myosin filaments but is due to an increase in the overlap between the filaments. The force is generated by millions of cross-bridges interacting with actin filaments (Fig. 13.6). The electron micrograph was kindly provided by Professor D.S. Smith. Figure 13.5 Electron micrograph of part of a longitudinal section of a myofibril. Identification of components and the mechanism of contraction. When a muscle fibre is stimulated to contract, the actin and myosin filaments react by sliding past each other but with no change in length of either myofilament. The thick myosin strands in the A band are relatively stationary, whereas the thin actin filaments, which are attached to the Z discs, extend further into the A band and may eventually obliterate the H band. Because the thin filaments are attached to Z discs, the discs are drawn toward each other, so that the sarcomeres, the distance between the adjacent Z-discs, are compressed, the myofibril is shortened, and contraction of the muscle occurs. Contraction, therefore, is not due to a shortening of either the actin or the myosin filaments but is due to an increase in the overlap between the filaments. The force is generated by millions of cross-bridges interacting with actin filaments (Fig. 13.6). The electron micrograph was kindly provided by Professor D.S. Smith.
The C-protein (thick filaments), myomesin (M-line protein), and a-actinin (Z-line protein)110113114 each provide 2% of the protein in the myofibril. Less than 1% each of 11 or more other proteins may also be present within the sarcomere.86115 Several of these, including the cytoskeletal proteins desmin and vimentin, and synemin surround the Z-discs.116/116a... [Pg.1099]

Myofibrils exhibit longitudinally repeating structures called sarcomeres. The fine structure of the sarcomere is described in figure 5.16. [Pg.111]

The vertebrate striated muscle Z-band is a cross-linking structure that links actin filaments of opposite polarity in successive sarcomeres along a myofibril. One of the curious things about it is that, unlike the A-band,... [Pg.42]

Furukawa, T., Ono, Y., and Tsuchiya, H. (2001). Specific interaction of the potassium channel beta-subunit minKwith the sarcomeric protein T-cap suggests a T-tubule-myofibril linking system. J. Mol. Biol. 313, 775-784. [Pg.115]

This armory affords consideration of the diffraction from the components of the muscle sarcomere. Note first that muscles are not single crystals of the kind illustrated in Fig. 3A. The sarcomeres themselves can have varying degrees of order some, like insect flight muscle and bony fish muscle, are almost crystalline within an A-band or sarcomere. But, whatever the muscle, both different myofibrils within a fiber, and different... [Pg.204]

Each cell within vertebrate striated muscle contains within its sarcoplasm many parallel myofibrils which in turn are made up of repeating sarcomere units. Within the sarcomere are the alternating dark A band and light I band, in the middle of which are the H zone and Z line, respectively. A myofibril contains two types of filaments the thick filaments consisting of myosin which are present only in the A band, and the thin filaments consisting of actin, tropomyosin and troponin. When muscle contracts, the thick and thin filaments slide over one another, shortening the length of the sarcomere. [Pg.391]

The thick filaments and the thin filaments of a myofibril partly interdigitatc with six thin filaments surrounding each thick filament. A single contractile unit, the sarcomere. is depicted in Fig. 5-32 and is about 1.5 yum in diameter and 2.2 /nm long. A linear arrangement of sarcomeres forms the myofibril, which, along with other myofibrils packed in parallel, can run the length of the muscle cell (up to several centimeters). [Pg.137]

Upon contraction, the thick and thin filaments in each sarcomere of each myofibril coordinately slide past each other without changing length. The sarcomeres shorten and the interdigitation between thick and thin filaments increases. This is the sliding filament model of muscle contraction. [Pg.137]

Fig. 5-32 Components of a skeletal muscle myofibril (a) myosin. (b) thick filament, and (c) the contraction of a sarcomere. The polarities of the thin filaments are indicated by the arrows. Fig. 5-32 Components of a skeletal muscle myofibril (a) myosin. (b) thick filament, and (c) the contraction of a sarcomere. The polarities of the thin filaments are indicated by the arrows.
A sarcomere is the basic unit of a muscle s cross-striated myofibril (Figure 17.4). Sarcomeres are the motor units of skeletal and cardiac muscle. They are multi-protein complexes composed of three different filament systems ... [Pg.267]

The sarcomeres are responsible for the striated appearance of skeletal and cardiac muscle. The myofibrils of smooth-muscle cells are not arranged into sarcomeres. [Pg.268]


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