A Experiment On Actin And Myosin

Smooth muscle contraction occurs when calcium is present in the smooth muscle cell and binds onto calmodulin to activate myosin light chain kinase (Wilson et al., 2002). Phosphorylation of myosin light chains result in myosin ATPase activity thus cross-bridge cycling occurs causing the muscle to contract (Horowitz et al., 1996). There are two known models of excitation and contraction in smooth muscle, electromechanical coupling (EMC) and pharmomechanical coupling

ATP is required to break the attachment of actin to the myosin head. At death, calcium ions leak out of the SR

Contractility of ASM requires an increased levels of intracellular Ca2+. When surface receptors are not activated, Ca2+ levels are low. Upon activation of these cell surface receptors by contractile agonists e.g. acetylcholine, serotonin and histamine, intracellular Ca2+ increases causing a contraction (9). Smooth muscle cell contraction is controlled by both receptor and mechanical activation of proteins actin and myosin and also changes to membrane potential.

Introduction: According to the “Human Physiology Laboratory Manual “,BIOL 282 ,page 31 , the reason of performing this experiment is to learn how the muscle contraction occurs based on the molecular level and what kind of factors are involved .As a matter of fact, skeletal muscles contain a lot of nuclei because of the cell fusion while being developed and are made of cylindrical cells that have myofibrils. The myofibrils contain sarcomeres and the

Muscle fibres, as shown in Diagram 1, consist of myofibrils, which contain the proteins, actin and myosin, in specific arrangements . The diagram illustrates how a muscle is made up of many fascicles, which in turn are made up of many endomysiums, and within them, many muscle fibres. Each muscle fibre is made up of many myofibrils that consist of sarcomeres bound end on end . Actin is a thin filament, about 7nm in diameter, and myosin is a thick filament, about 15nm in diameter , both of which reside in the sarcomere. They are held together by transverse bands known as Z lines . Diagram 2 shows actin and myosin filaments within a sarcomere, and the Z lines that connect them.

Myofibrils are made up of long proteins that include myosin, titin, and actin while other proteins bind them together. These proteins are arranged into thin and thick filaments that are repetitive along the myofibril in sectors known as sarcomeres. The sliding of actin and myosin filaments along each other is when the muscle is contracting. Dark A-bands and light I-bands reappear along myofibrils. The alignment of myofibrils causes an appearance of the cell to look banded or striated. A myofibril is made up of lots of sarcomeres. As the sarcomeres contract individually the muscle cells and myofibrils shorten in length. The longitudinal section of skeletal muscle exhibits a unique pattern of alternating light and dark bands. The dark staining, A-bands possess a pale region in the middle called the H-zone. In the middle of the H-zone the M-line is found, that displays filamentous structures that can join the thick filaments. The light-staining bands also known as I-bands are divided by thin Z-line. These striated patterns appear because of the presence of myofibrils in the sarcoplasm (IUPUI, 2016).

Rationale, Significance and Hypothesis. An extrinsic factor, which exerts a dominant influence on skeletal muscle fiber phenotype, is the nervous system. Buller et al. (1960) elegantly demonstrated the plastic nature of skeletal muscle fibers in response to changes in innervation type. Later, Lφmo and Westgaard (Lφmo and Westgaard, 1974; Westgaard and Lφmo, 1988) demonstrated that depolarization of muscle with specific patterns and frequencies of electrical activity are sufficient to cause changes in mature muscle fiber phenotypes. However, how myofibrillar gene expression and structural organization is affected by the frequency of impulses during activity, the amount of activity over time, or other characteristics of patterned activity is essentially unknown. To answer these questions will require the isolation and study of subsets of muscle-specific proteins in relation to different electrical activation patterns in vivo, an issue that cannot be easily addressed in preparations currently used in the study of muscle development and maintenance. However, using novel in vivo approaches can, in part, circumvent this difficulty.

Martini, F. H., Nath, J. L., and Bartholomew, E. F. “Muscle Tissue.” Anatomy & Physiology. 9th

The power stroke is responsible for the contraction of the muscle and force generation. ATP binding to the myosin head detaches the myosin head from the actin filament and allows the cycle to repeat. The coordinated contraction and relaxation of many muscles in an antagonistic fashion is the basis for the kinematics of any movement.

ith the myosin have been activated by the ATP, they will bind the action binding site.

This activity is the critical driving force of muscle contraction. The stream of action potentials along the muscle fiber surface is terminated as Acetylcholine at the neuromuscular junction is broken down by acetyl cholinesterase. The release of Calcium ions is ceased. The action of the myosin molecule heads is obstructed because of the change in the configuration of troponin and tropomyosin due to the absence of calcium ions. This will eventually cause the contraction to be ceased. Together with these physical processes, an external stretching force such as gravity pulls the muscle back to its normal length.

-Muscles contract in a repeated pattern of binding and releasing between the two thin and thick strands of the sarcomere. ATP is critical to prepare myosin for binding and to recharge the myosin. The source

Immunohistochemical analysis for smooth muscle actin (SMA) was done and the intensity of staining and staining location were considered.

twitch muscles. Fast twitch muscles have a fast form of myosin ATP and are very

Both of these muscles expand and contract as they have complex structures so it is essential how they do this. The cardiac muscle needs the contractions to occur in order to pump blood out of the atria and into the ventricles and round the circulatory system so the structure of this muscle shows the systole of the heart. The contractions of the skeletal muscle also depend on its structure. The binding and releasing of two strands of sarcomere is how the repeated pattern of contractions occurs. ATP is used to prepare myosin for binding to allow the contractions to happen. The skeletal and cardiac muscle also both has elasticity. The elasticity is used to restore the muscles back to their original lengths which enable them to resume back to their original length once they have contracted and been stretched.