Muscle contraction sliding filament

FIGURE 5-32 Muscle contraction. Thick filaments are bipolar structures created by the association of many myosin molecules, (a) Muscle contraction occurs by the sliding of the thick and thin filaments... 

See also The Structure of Muscle, The Sliding Filament Model, The Role of Calcium in Contraction, Transverse Tubules... 

Figure 14.11 The sliding filament model of muscle contraction. The actin (red) and myosin (green) filaments slide past each other without shortening.

Figure 14.12 The swinging cross-bridge model of muscle contraction driven by ATP hydrolysis, (a) A myosin cross-bridge (green) binds tightly in a 45 conformation to actin (red), (b) The myosin cross-bridge is released from the actin and undergoes a conformational change to a 90 conformation (c), which then rebinds to actin (d). The myosin cross-bridge then reverts back to its 45° conformation (a), causing the actin and myosin filaments to slide past each other. This whole cycle is then repeated.

Studies on muscle contraction carried out between 1930 and 1960 heralded the modem era of research on cytoskeletal stmctures. Actin and myosin were identified as the major contractile proteins of muscle, and detailed electron microscopic studies on sarcomeres by H.E. Huxley and associates in the 1950s produced the concept of the sliding filament model, which remains the keystone to an understanding of the molecular mechanisms responsible for cytoskeletal motility. 

Development of the Sliding Filament Theory of Muscle Contraction... 

DEVELOPMENT OF THE SLIDING FILAMENT THEORY OF MUSCLE CONTRACTION... 

The ability of S-2 to act as a flexible link also explained another problem in muscle contraction. When muscle contracts its volume remains constant. As a muscle shortens, and the filaments slide past each other, the spacing between the filaments increases as part of this constant volume behavior. Therefore, the crossbridges have to be able to interact with actin over a wide range of filament spacings. The presence of the flexible link in S-2 would allow this to occur. 

The Sliding Filament Cross-Bridge Model Is the Foundation on Which Current Thinking About Muscle Contraction Is Built... 

Describe the sliding filament theory of skeletal muscle contraction... 

The mechanism of skeletal muscle contraction is described by the Sliding Filament Theory (see Figure 11.2). This mechanism begins with the "priming ... 

A. Huxley and Niedergerke, H.E.Huxley and Hanson. The sliding filament theory of muscle contraction. 

The sliding filament model describes the mechanism involved in muscle contraction. In this model, sarcomeres become shorter when the thin and thick filaments slide alongside each other and telescope together, with ATP being consumed. During contraction, the following reaction cycle is repeated several times ... 

Because there are many myosin heads in a thick filament, at any given moment some (probably 1% to 3%) are bound to the thin filaments. This prevents the thick filaments from slipping backward when an individual myosin head releases the actin subunit to which it was bound. The thick filament thus actively slides forward past the adjacent thin filaments. This process, coordinated among the many sarcomeres in a muscle fiber, brings about muscle contraction. 

FIGURE 5-33 Molecular mechanism of muscle contraction. Conformational changes in the myosin head that are coupled to stages in the ATP hydrolytic cycle cause myosin to successively dissociate from one actin subunit, then associate with another farther along the actin filament. In this way the myosin heads slide along the thin filaments, drawing the thick filament array into the thin filament array (see Fig. 5-32). 

Contraction-relaxation processes in muscle proceed by a sliding filament mechanism, whereby actin and myosin filament move relative to one another. The reaction is energized by ATP and regulated by the level of calcium ions. In vertebrate skeletal muscle contraction is controlled by the interaction of calcium ions with the specific protein troponin which is attached to the actin filaments, whereas among many invertebrates troponin is lacking and myosin and not actin is controlled192. However, in a few invertebrates both types of filaments are involved in regulation. 

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