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Chapter 2 Structure of Muscle Tissue and Muscle Contraction

Chapter 2 Structure of Muscle Tissue and Muscle Contraction. The three types of human muscle tissue. Smooth, nonstriated muscle is found in the walls of the hollow viscera and blood vessels.

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Chapter 2 Structure of Muscle Tissue and Muscle Contraction

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  1. Chapter 2 Structure of Muscle Tissue and Muscle Contraction

  2. The three types of human muscle tissue • Smooth, nonstriated muscle is found in the walls of the hollow viscera and blood vessels. • Skeletal, striated muscle is attached to the skeleton and provides the force for movement of the bony leverage system. • Cardiac, striated muscle is found only in the heart.

  3. Skeletal muscle fibers showing cross-striations

  4. Muscle fibers and connective tissue sheaths

  5. Muscle fiber types are classified by • Anatomical appearance:red versus white • Muscle function:fast-slow or fatigable versus fatigue resistant • Biochemical properties:such as high or low aerobic capacity • Histochemical properties:such as enzyme profile

  6. The structure of smooth muscle is characterized by • Long, spindle-shaped fibers • An external shape that may change to conform to the surrounding elements • One nucleus per fiber

  7. Characteristics of the structure of skeletal muscle • The muscle is made up of long, cylindrical fibers. • Each fiber is a large cell with up to several hundred nuclei. • Each cell is structurally independent of its neighboring fiber or cell. • The muscle has cross-striations of alternating light and dark bands.

  8. The structure of cardiac muscle is characterized by • A network (syncytium) of striated muscle fibers. • Discrete fibers that can contract individually. • A network of fibers that responds to innervations with a wavelike contraction that passes through the entire muscle.

  9. The three primary fiber types in human skeletal muscle • Slow twitch oxidative (SO) • Fast twitch oxidative glycolytic (FOG) • Fast twitch glycolytic (FG) For more information, visit Muscle Histology atwww.unomaha.edu/~swick/2740musclehistology.htmland Histology of Muscle athttp://views.vcu.edu/ana/OB/Muscle~1/index.htm

  10. Characteristics of muscle fiber types

  11. Structure of the myofibril • Sarcomere • functional unit • composed of two types of parallel myofilaments • Myosin • Actin • Z-line • membrane that separates sarcomeres • A band • dark band seen as part of striation • H zone • amount by which the two ends of the thin filaments fail to meet • I band • area between the ends of the myosin • light band in the striation

  12. A sarcomere extends from Z-line to Z-line. Also shown are the A, H, and I bands that give skeletal muscle its striated appearance.

  13. Contractile proteins actin, myosin, troponin, and tropomyosin

  14. Significance of fiber-type composition for athletes • High percentage of SO fibers—candidate for distance running or other endurance sports • High percentage of FT fibers—candidate for power or sprint events • Percentage is genetically determined

  15. Series of events that lead to muscle contraction in the sliding filament model • At Rest • Tropomyosin inhibits actin-myosin binding. • Calcium is stored in the sarcoplasmic reticulum. • Neural stimulation causes the sarcoplasmic reticulum to release calcium. • Calcium binds to troponin, which removes the inhibitory effect of tropomyosin and actin-myosin bind. • Myosin cross-bridges swivel, pulling the actin and z-lines. • Fresh ATP binds to the myosin cross-bridges, leading to cross-bridge recycling. • Neural stimulation ceases and relaxation occurs. Contraction

  16. Theory 1 • Actin-myosin bind Activates myosin ATPase Breakdown of ATP molecule liberates energy • Energy causes myosin cross-bridge to swivel to center of sarcomere Myosin is bound to actin, which is bound to Z-lines Z-lines pulled closer together Sarcomere shortened • Fresh ATP molecule binds to myosin cross-bridge Actin-myosin binding released Myosin cross-bridge stands back up • Actin-myosin rebinds at new site Activates myosin ATPase Breakdown of ATP molecule liberates energy • And process repeats

  17. Theory 2 • Myosin cross-bridge stores energy from breakdown of ATP by myosin ATPase Actin-myosin binding releases stored energy • Causes myosin cross-bridge to swivel ADP and Pi are released from the myosin cross-bridge • Fresh ATP molecule binds to myosin cross-bridge Actin-myosin binding released ATP is broken down and energy causes myosin cross-bridge to stand back up (re-energized) • Fresh ATP molecule is broken down Energy reenergizes myosin cross-bridge • Process repeats

  18. Comparing the two theories • Both theories state that fresh ATP binds to the myosin cross-bridge to release it from actin during cross-bridge recycling. • Theory 2 states that after the myosin-actin binding is released, the fresh ATP molecule is broken down and the energy released is used to reenergize the myosin cross-bridge. • According to Theory 1, energy is not needed to cause the myosin cross-bridge to stand back up.

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