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Structure of Skeletal Muscle Presentation by: Angela Holloman.

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1 Structure of Skeletal Muscle Presentation by: Angela Holloman

2 Introduction All activities that involve movement depend on muscles 650 muscles in the human body Various purposes for muscles for: –Locomotion –Upright posture –Balancing on two legs –Support of internal organs –Controlling valves and body openings –Production of heat –Movement of materials along internal tubes Three types of muscles in the human body –Skeletal –Cardiac –Smooth

3 Skeletal Muscle Skeletal muscles are muscles which are attached to the skeleton. 40% of human body mass Skeletal muscles are mainly responsible for locomotion, and voluntary contraction and relaxation.

4 Structure of Skeletal muscles Skeletal muscles are composed of clusters of muscle cells. –Muscle fibers –Myofibers –Myocytes A muscle consists of packages of muscle cells called fascicles A muscle cell is long and spindle shaped

5 Structure of Skeletal muscles Cell structure –Muscles cells contain many nuclei –The plasma membrane→ sarcolemma –The cytoplasm→ sarcoplasm –Length –ranges from 0.1cm to more the 30cm in length –Diameter –ranges from 0.001cm to 0.01cm in diameter Myofibrils→ –elongated protein molecules –aligned in parallel arrangements –extend the full length of the cell.



8 Structure of Skeletal muscles The myofibril consists of protein chains called myofilaments –Myofilaments have a symmetrical, alternating pattern of thick and thin elements.

9 Skeletal Muscle Myosin Thick myofilament consists of a large number of bundled myosin molecules aligned in overlapping arrays. hexameric proteins with two identical heavy chains and two pairs of different light chains. –regulatory light chain (RLC) –essential light chain (ELC)

10 Skeletal Muscle Actin The thin myofilament (F-actin, filamentous actin) –made up of two helically intertwined chains of G-actin (globular actin) units. Other proteins that bind to the actin molecules: Tropomyosin The Troponin complex→ made up of three members


12 Contraction of Skeletal Muscle The thick and thin filaments, along with their associated myofibril proteins, are responsible for muscle contraction. How does muscle contraction work? –Influx of calcium ions in the cell as a result of nerve impulses –troponin complex pulls tropomyosin molecules away from the G-actin subunits –Exposure of the myosin binding sites. –The heads of the myosin molecules can bind to the actin subunits, forming cross bridges. active site in each myosin head disrupts the high-energy bond of ATP molecules release of energy moves the myosin head towards the F- actin, when contact is made with the actin subunits, the F-actin is pulled along, causing the myofilament to contract. The coordinated contraction of all the myofilaments of all the muscle cells of a muscle, causes the entire muscle to contract.


14 Relaxation of Skeletal Muscle –Calcium ions are carried away from the myofilaments –Myosin- actin linkages loosen –The troponin complex and tropomyosin bind to the myosin binding sites on the F-actin subunits, Myosin and F- actin myofilaments return to their original positions

15 References: Pasternak, Jack J. Human Molecular Genetics: Mechanisms of Inherited Diseases. Hoboken, New Jersey: John Wilkey & Sons Inc., 2005. March, 20, 2006

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