Sarcomeres electron micrograph

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)... 

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 19-6 (A) The structure of a typical sarcomere of skeletal muscle. The longitudinal section depicted corresponds to that of the electron micrograph, Fig. 19-7A. The titin molecules in their probable positions are colored green. The heads of only a fraction of the myosin molecules are shown protruding toward the thin actin filaments with which they interact.

Electron micrograph of a striated muscle sarcomere showing the appearance of filamentous structures when cross-sectioned at the locations illustrated below. (Electron micrograph courtesy of Dr. Hugh Huxley, Brandeis University.)... 

Fig. 5. (A) Electron micrograph picture showing a whole sarcomere from fish...

Fig. 1. Layout of titin in the sarcomere. Center panel electron micrograph of sarcomere of stretched soleus muscle fiber, labeled with anti-titin antibodies that demarcate the tandem Ig and PEVK spring elements of titin s extensible I-band region. Superimposed are two schematic titin molecules (one for each half sarcomere). Top and bottom panels domain structure of I-band and A-band sequence of titin, respectively (from Labeit and Kolmerer, 1995). Bottom left length of tandem Ig segment (proximal + distal segment) and PEVK segment in human soleus fibers, as function of sarcomere length (based on Trombitas et al., 1998b).

Figure 34.13. Sarcomere. (A) Electron micrograph of a longitudinal section of a skeletal muscle myofibril, showing a single sarcomere. (B) Schematic representations of cross sections correspond to the regions in the micrograph. [Courtesy of Dr. Hugh Huxley. ]...

In recent years the biological importance of the cytoskeletal structures—microtubules, intermediate filaments, and microfilaments (actin)—has attracted the attention of many cell biologists. In striated muscle, myosin and actin filaments together with Z lines are the main cytoskeletal structures to form sarcomeres of the myofibril. However, myosin and actin are contractile proteins, and some of the proteins constituting the Z line are classified as actin-associated proteins. Therefore, cell membrane attachment proteins, intermediate filaments, and some other structural proteins are described in this section. There has not been any report on muscle microtubules, although their presence is shown in some electron micrographs of sectioned samples. 

Identify the A band, H zone, M line, I band, and Z line of a sarcomere in an electron micrograph of a myofibril. 

The symmetry of thick and thin filaments in a sarcomere is such that six thin filaments ordinarily surround each thick filament in a hexagonal array. (See Figure 34.13 on p. 957 of the text.) In electron micrographs of cross-sections of fully contracted muscle, the ratio between thin and thick filaments has been found to be double that of resting muscle. 

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