Structure of Skeletal Muscle - Bellarmine University

Structure of Skeletal Muscle - Bellarmine University

Structure of Skeletal Muscle Presentation by: Angela Holloman 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

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. 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 Structure of Skeletal muscles Cell structure

Muscles cells contain many nuclei The plasma membrane sarcolemma The cytoplasm sarcoplasm Length Diameter

ranges from 0.1cm to more the 30cm in length ranges from 0.001cm to 0.01cm in diameter Myofibrils elongated protein molecules aligned in parallel arrangements extend the full length of the cell. Structure of Skeletal muscles

The myofibril consists of protein chains called myofilaments Myofilaments have a symmetrical, alternating pattern of thick and thin elements. 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) 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 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. 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 References: Pasternak, Jack J. Human Molecular Genetics: Mechanisms of Inherited Diseases. Hoboken, New Jersey: John Wilkey & Sons Inc., 2005. http://www.lau-verlag.de/anatom/muscleb.jpg. March, 20, 2006

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