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MUSCLES- About this Chapter

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This chapter delves into the three primary types of muscles: skeletal, smooth, and cardiac. It highlights the structure and function of skeletal muscles, which account for 40-50% of body weight and play a crucial role in locomotion, posture, and heat production. The anatomy of skeletal muscle involves various components such as muscle fibers, myofibrils, actin, myosin, and the sliding filament model of contraction. The microstructure, including sarcomeres and cross-bridge formation, is essential for understanding how muscles contract and generate force.

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MUSCLES- About this Chapter

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  1. MUSCLES-About this Chapter • Skeletal muscle • Mechanics of body movement • Smooth muscle • Cardiac muscle

  2. The Three Types of Muscle Figure 12-1a

  3. The Three Types of Muscle Figure 12-1b

  4. The Three Types of Muscle Figure 12-1c

  5. Skeletal Muscle • Human body contains over 400 skeletal muscles • 40-50% of total body weight • Functions of skeletal muscle-Genrates • Force for locomotion and breathing • Force production for postural support • Heat production during cold stress

  6. Anatomy Summary: Skeletal Muscle Figure 12-3a (2 of 2)

  7. Fascicles: bundles, CT(connective tissue) covering on each one • Muscle fibers: muscle cells

  8. Structure of Skeletal Muscle:Microstructure • Sarcolemma • Transverse (T) tubule • Longitudinal tubule (Sarcoplasmic reticulum, SR) • Myofibrils • Actin(thin filament) • Troponin • Tropomyosin • Myosin(thick filament)

  9. Within the sarcoplasm Triad • Transverse tubules • Sarcoplasmic reticulum -Storage sites for calcium • Terminal cisternae - Storage sites for calcium

  10. Microstructure of Skeletal Muscle (myofibril)

  11. Sarcomeres • Sarcomere:bundle of alternating thick and thin filaments • Sarcomeres join end to end to form myofibrils • Thousands per fiber, depending on length of muscle • Alternating thick and thin filaments create appearance of striations

  12. Myosin • Myosin head is hinged • Bends and straightens during contraction

  13. Thick filaments (myosin) • Bundle of myosin proteins shaped like double-headed golf clubs • Myosin heads have two binding sites • Actin binding site forms cross bridge • Nucleotide binding site binds ATP (Myosin ATPase) • Hydrolysis of ATP provides energy to generate power stroke

  14. Thin filaments

  15. Thin filaments (actin) • Backbone: two strands of polymerizedglobularactin – fibrous actin • Each actin has myosin binding site • Troponin • Binds Ca2+; regulates muscle contraction • Tropomyosin • Lies in groove of actin helix • Blocks myosin binding • sites in absence of Ca2+

  16. Thick filament: Myosin (head and tail) • Thin filament: Actin, Tropomyosin, Troponin (calcium binding site)

  17. III Molecular Mechanism of Muscular Contraction • The sliding filament model • Muscle shortening is due to movement of the actin filament over the myosin filament • Reduces the distance between Z-lines

  18. The Sliding Filament Model of Muscle Contraction

  19. Changes in the appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber

  20. Cross-Bridge Formation in Muscle Contraction

  21. Energy for Muscle Contraction • ATP is required for muscle contraction • Myosin ATPase breaks down ATP as fiber contracts

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