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Chapter 12a

Chapter 12a. Muscles. About this Chapter. Skeletal muscle Mechanics of body movement Smooth muscle Cardiac muscle. Three Types of Muscle. Nucleus. Muscle fiber (cell). Striations. (a) Skeletal muscle . Figure 12-1a. Three Types of Muscle. Striations. Muscle fiber. Intercalated disk.

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Chapter 12a

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  1. Chapter 12a Muscles

  2. About this Chapter • Skeletal muscle • Mechanics of body movement • Smooth muscle • Cardiac muscle

  3. Three Types of Muscle Nucleus Muscle fiber(cell) Striations (a) Skeletal muscle Figure 12-1a

  4. Three Types of Muscle Striations Muscle fiber Intercalated disk Nucleus (b) Cardiac muscle Figure 12-1b

  5. Three Types of Muscle Muscle fiber Nucleus (c) Smooth muscle Figure 12-1c

  6. Skeletal Muscle • Usually attached to bones by tendons • Origin: closest to the trunk • Insertion: more distal • Flexor: brings bones together • Extensor: moves bones away • Antagonistic muscle groups: flexor-extensor pairs

  7. Antagonistic Muscle Groups Tricepsmusclerelaxes Biceps musclecontracts (flexor) (a) Flexion Figure 12-2a

  8. Antagonistic Muscle Groups Triceps musclecontracts (extensor) Bicepsmusclerelaxes (b) Extension Figure 12-2b

  9. Organization of Skeletal Muscle Skeletal muscle Nerve andblood vessels Tendon Connective tissue Muscle fascicle:bundle of fibers Connectivetissue Nucleus Muscle fiber (a) Figure 12-3a (1 of 2)

  10. Organization of Skeletal Muscle Figure 12-3a (2 of 2)

  11. Ultrastructure of Muscle ANATOMY SUMMARY ULTRASTRUCTURE OF MUSCLE Mitochondria Sarcoplasmicreticulum Thickfilament Thinfilament Nucleus T-tubules Myofibril Sarcolemma (b) A band Sarcomere Z disk Z disk Myofibril (c) M line I band H zone Titin (d) Z disk Z disk M line Myosincrossbridges M line Thick filaments Thin filaments Titin (e) Troponin Nebulin Myosin heads Hingeregion Myosin tail Tropomyosin G-actin molecule Actin chain Myosin molecule (f) Figure 12-3b-f

  12. Ultrastructure of Muscle ULTRASTRUCTURE OF MUSCLE Mitochondria Sarcoplasmicreticulum Thickfilament Thinfilament Nucleus T-tubules Myofibril Sarcolemma (b) Figure 12-3b

  13. Ultrastructure of Muscle Sarcomere A band Z disk Z disk Myofibril (c) M line H zone I band Figure 12-3c

  14. Ultrastructure of Muscle Titin (d) Z disk Z disk Myosincrossbridges M line Figure 12-3d

  15. Ultrastructure of Muscle M line Thick filaments (e) Myosin heads Hinge region Myosin tail Myosin molecule Figure 12-3e

  16. Ultrastructure of Muscle Thin filaments Titin Troponin Nebulin Tropomyosin G-actin molecule Actin chain (f) Figure 12-3f

  17. Ultrastructure of Muscle Sarcomere A band Z disk Z disk Myofibril (c) M line H zone I band Titin (d) Z disk Z disk Myosin crossbridges M line M line Thick filaments Thin filaments Titin (e) Troponin Nebulin Myosin heads Hinge region Myosin tail Tropomyosin G-actin molecule Myosin molecule Actin chain (f) Figure 12-3c-f

  18. T-Tubules and the Sarcoplasmic Reticulum T-tubule brings actionpotentials into interiorof muscle fiber. Thin filament Thick filament Sarcolemma Triad Sarcoplasmic reticulumstores Ca2+ Terminalcisterna Figure 12-4

  19. The Two- and Three-Dimensional Organization of a Sarcomere Sarcomere A band I band H zone I band Thin filament Thick filament (a) M line Z disk Z disk (b) Z disk Z disk I bandthin filamentsonly H zonethick filamentsonly M linethick filamentslinked withaccessory proteins Outer edgeof A bandthick and thinfilaments overlap (c) Figure 12-5

  20. Anatomy Review Animation PLAY Interactive Physiology® Animation: Muscular System: Anatomy Review: Skeletal Muscle Tissue

  21. Muscle Contraction • Muscle tension: force created by muscle • Load: weight that opposes contraction • Contraction: creation of tension in muscle • Relaxation: release of tension • Steps leading up to muscle contraction: • Events at the neuromuscular junction • Excitation-contraction coupling • Contraction-relaxation cycle

  22. Summary of Muscle Contraction Figure 12-7

  23. Events at the Neuromuscular Junction PLAY Events at the Neuromuscular Junction PLAY Interactive Physiology® Animation: Muscular System: Events at the Neuromuscular Junction

  24. Changes in a Sarcomere During Contraction I band Myosin Z Z A band Actin Musclerelaxed Zline Z M Z A band Half ofI band H zone Half ofI band Sarcomere shortenswith contraction Half ofI band Mline Zline H Z Z A band constant Musclecontracted I H I H zone and I band both shorten Figure 12-8

  25. Sliding Filament Theory PLAY Interactive Physiology® Animation: Muscular System: Sliding Filament Theory

  26. The Molecular Basis of Contraction Troponin G-Actin TN Myosin head Tropomyosinblocks bindingsite on actin ADP Pi (a) Relaxed state. Myosin head cocked. Figure 12-9a

  27. The Molecular Basis of Contraction 1 Cytosolic Ca2+ 1 Ca2+ levels increase in cytosol. 3 Tropomyosin shifts, exposing binding site on actin 2 2 Ca2+ binds to troponin (TN). TN 3 Troponin-Ca2+ complex pulls tropomyosin away from actin’s myosin-binding site. 5 Actin moves ADP 4 Power stroke Pi 4 Myosin binds to actin and completes power stroke. 5 Actin filament moves. (b) Initiation of contraction Figure 12-9b

  28. The Molecular Basis of Contraction G-actin molecule Myosinbinding sites Myosinfilament ATP binds to myosin.Myosin releases actin. 1 Tight binding in the rigor state ATP ADP Myosin hydrolyses ATP. Myosinhead rotates and binds to actin. 2 Myosin releases ADP. 4 Contraction-relaxation Actin filament movestoward M line. Sliding filament ADP Pi Ca2+signal Pi Power stroke 3 Relaxed state with myosin heads cocked Figure 12-10

  29. The Molecular Basis of Contraction G-actin molecule Myosin binding sites Myosin filament Tight binding in the rigor state Figure 12-10, step 0

  30. The Molecular Basis of Contraction G-actin molecule Myosin binding sites Myosin filament ATP binds to myosin. Myosin releases actin. 1 T ight binding in the rigor state ATP Figure 12-10, steps 0–1

  31. The Molecular Basis of Contraction ATP binds to myosin. Myosin releases actin. Myosin hydrolyses ATP. Myosin head rotates and binds to actin. 1 2 ADP ATP Pi Relaxed state with myosin heads cocked Figure 12-10, steps 1–2

  32. The Molecular Basis of Contraction Myosin hydrolyses ATP. Myosin head rotates and binds to actin. Power stroke 3 2 Actin filament moves toward M line. Ca2+ signal ADP Pi Pi Relaxed state with myosin heads cocked Figure 12-10, steps 2–3

  33. The Molecular Basis of Contraction Power stroke Myosin releases ADP. 3 4 Actin filament moves toward M line. ADP Pi Figure 12-10, steps 3–4

  34. Excitation-Contraction Coupling Axon terminal of somatic motor neuron 1 Somatic motor neuron releases ACh at neuromuscular junction. 1 Muscle fiber ACh 2 2 Net entry of Na+ through ACh receptor-channel initiates a muscle action potential Na+ Motor end plate RyR T-tubule Sarcoplasmic reticulum Ca2+ DHP Z disk Troponin Actin Tropomyosin M line Myosin head Myosin thick filament (a) Initiation of muscle action potential KEY RyR = ryanodine receptor-channel DHP = dihydropyridine L-type calcium channel Figure 12-11a

  35. Excitation-Contraction Coupling Axon terminal of somatic motor neuron 1 Somatic motor neuron releases ACh at neuromuscular junction. 1 Muscle fiber ACh Motor end plate RyR T-tubule Sarcoplasmic reticulum Ca2+ DHP Z disk Troponin Actin Tropomyosin M line Myosin head Myosin thick filament (a) Initiation of muscle action potential KEY RyR = ryanodine receptor-channel DHP = dihydropyridine L-type calcium channel Figure 12-11a, step 1

  36. Excitation-Contraction Coupling Axon terminal of somatic motor neuron 1 Somatic motor neuron releases ACh at neuromuscular junction. 1 Muscle fiber ACh 2 2 Net entry of Na+ through ACh receptor-channel initiates a muscle action potential Na+ Motor end plate RyR T-tubule Sarcoplasmic reticulum Ca2+ DHP Z disk Troponin Actin Tropomyosin M line Myosin head Myosin thick filament (a) Initiation of muscle action potential KEY RyR = ryanodine receptor-channel DHP = dihydropyridine L-type calcium channel Figure 12-11a, steps 1–2

  37. Excitation-Contraction Coupling Action potential in t-tubule alters conformation of DHP receptor. 3 4 DHP receptor opens RyR Ca2+ release channels in sarcoplasmic reticulum and Ca2+ enters cytoplasm. 4 3 Ca2+ binds to troponin, allowing actin-myosin binding. 5 Ca2+ released 7 5 Myosin heads execute power stroke. 6 6 Actin filament slides toward center of sarcomere. Myosin thick filament 7 Distance actin moves KEY (b) Excitation-contraction coupling DHP = dihydropyridine L-type calcium channel RyR = ryanodine receptor-channel Figure 12-11b

  38. Electrical and Mechanical Events in Muscle Contraction • A twitch is a single contraction-relaxation cycle Muscle fiber +30 Action potentialfrom CNS Neuronmembranepotentialin mV -70 Motorend plate Time Recordingelectrodes +30 Axonterminal Muscle fibermembranepotentialin mV Muscle actionpotential -70 2msec Time Latentperiod Relaxationphase Contractionphase Developmentof tensionduring onemuscle twitch Tension 10–100 msec Time Figure 12-12

  39. Phosphocreatine Creatine phosphate Glycolysis Krebs cycle Figure 12-13

  40. Locations and Possible Causes of Muscle Fatigue Figure 12-14

  41. Causes of Muscle Fatigue During Exercise • Extended submaximal exercise • Depletion of glycogen stores • Short-duration maximal exertion • Increased levels of inorganic phosphate • May slow Pi release from myosin • Decrease calcium release • Maximal exercise • Potassium (K+) leaves muscle fiber, leading to increased concentration that is believed to decrease Ca2+

  42. Skeletal Muscle Metabolism During Fatiguing Submaximal Exercise Question 12-1

  43. Fast-Twitch Glycolytic and Slow-Twitch Oxidative Muscle Fibers Figure 12-15

  44. Fast-Twitch Glycolytic and Slow-Twitch Oxidative Muscle Fibers Table 12-2

  45. Length-Tension Relationships in Contracting Skeletal Muscle Figure 12-16

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