1. Muscle  Lecture #10 Ch 10 Muscle Muse 6/20/12

2. An Introduction to Muscle Tissue  Muscle Tissue  A primary tissue type, divided into  Skeletal muscle  Cardiac muscle  Smooth muscle

3. Functions of Skeletal Muscles  Produce skeletal movement  Maintain body position  Support soft tissues  Guard openings  Maintain body temperature  Store nutrient reserves

4. Skeletal Muscle Structures  Muscle tissue (muscle cells or fibers)  Connective tissues  Nerves  Blood vessels

5. Skeletal Muscle Structures  Organization of Connective Tissues  Muscles have three layers of connective tissues  Epimysium: –exterior collagen layer –connected to deep fascia –Separates muscle from surrounding tissues  Perimysium: (not to be confused with paramecium) –surrounds muscle fiber bundles (fascicles) –contains blood vessel and nerve supply to fascicles  Endomysium: –surrounds individual muscle cells (muscle fibers) –contains capillaries and nerve fibers contacting muscle cells –contains myosatellite cells (stem cells) that repair damage

6. Skeletal Muscle Structures Figure 10–1 The Organization of Skeletal Muscles.

7. Figure 9.1 Bone Perimysium Endomysium (between individual muscle fibers) Muscle fiber Fascicle (wrapped by perimysium) Epimysium Tendon Epimysium Muscle fiber in middle of a fascicle Blood vessel Perimysium Endomysium Fascicle (a) (b)

8. Skeletal Muscle Structures  Organization of Connective Tissues  Muscle attachments  Endomysium, perimysium, and epimysium come together: –at ends of muscles –to form connective tissue attachment to bone matrix –i.e., tendon (bundle) or aponeurosis (sheet)

9. Skeletal Muscle Structures  Nerves  Skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system (brain and spinal cord)  Blood Vessels  Muscles have extensive vascular systems that  Supply large amounts of oxygen  Supply nutrients  Carry away wastes

10. Skeletal Muscle: Attachments  Muscles attach:  Directly—epimysium of muscle is fused to the periosteum of bone or perichondrium of cartilage  Indirectly—connective tissue wrappings extend beyond the muscle as a ropelike tendon or sheetlike aponeurosis

11. Skeletal Muscle Fibers  Are very long  Develop through fusion of mesodermal cells (myoblasts)  Become very large  Contain hundreds of nuclei

12. Skeletal Muscle Fibers Figure 10–2 The Formation of a Multinucleate Skeletal Muscle Fiber.

13. Skeletal Muscle Fibers Figure 10–2a The Formation of a Multinucleate Skeletal Muscle Fiber.

14. Skeletal Muscle Fibers Figure 10–2b The Formation of a Multinucleate Skeletal Muscle Fiber.

15. Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  The sarcolemma  The cell membrane of a muscle fiber (cell)  Surrounds the sarcoplasm (cytoplasm of muscle fiber)  A change in transmembrane potential begins contractions

16. NucleusLight I bandDark A band Sarcolemma Mitochondrion (b) Diagram of part of a muscle fiber showing the myofibrils. One myofibril is extended afrom the cut end of the fiber. Myofibril

17. Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Transverse tubules (T tubules)  Transmit action potential through cell  Allow entire muscle fiber to contract simultaneously  Have same properties as sarcolemma

18. Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Myofibrils  Lengthwise subdivisions within muscle fiber  Made up of bundles of protein filaments (myofilaments)  Myofilaments are responsible for muscle contraction  Types of myofilaments: –thin filaments: »made of the protein actin –thick filaments: »made of the protein myosin

19. Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Sarcoplasmic reticulum (SR)  A membranous structure surrounding each myofibril  Helps transmit action potential to myofibril  Similar in structure to smooth endoplasmic reticulum  Forms chambers (terminal cisternae) attached to T tubules

20. Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Triad  Is formed by one T tubule and two terminal cisternae  Cisternae: –concentrate Ca 2+ (via ion pumps) –release Ca 2+ into sarcomeres to begin muscle contraction

21. Skeletal Muscle Fibers Figure 10–3 The Structure of a Skeletal Muscle Fiber. Show video excitation coupling

22. Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Sarcomeres  The contractile units of muscle  Structural units of myofibrils  Form visible patterns within myofibrils  Muscle striations  A striped or striated pattern within myofibrils: –alternating dark, thick filaments (A bands) and light, thin filaments (I bands)

23. Sarcomere  Smallest contractile unit (functional unit) of a muscle fiber  The region of a myofibril between two successive Z discs  Composed of thick and thin myofilaments made of contractile proteins

24. Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Sarcomeres  M Lines and Z Lines: –M line: »the center of the A band »at midline of sarcomere –Z lines: »the centers of the I bands »at two ends of sarcomere

25. I band A band Sarcomere H zone Thin (actin) filament Thick (myosin) filament Z disc M line (c) Small part of one myofibril enlarged to show the myofilaments responsible for the banding pattern. Each sarcomere extends from one Z disc to the next. Z disc M line Sarcomere Thin (actin) filament Thick (myosin) filament Elastic (titin) filaments (d) Enlargement of one sarcomere (sectioned lengthwise). Notice the myosin heads on the thick filaments.

26. Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Sarcomeres  Zone of overlap: –the densest, darkest area on a light micrograph –where thick and thin filaments overlap  The H Band: –the area around the M line –has thick filaments but no thin filaments

27. Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Sarcomeres  Titin: –are strands of protein- quite elastic, like springs –reach from tips of thick filaments to the Z line –stabilize the filaments

28. Skeletal Muscle Fibers Figure 10–4a Sarcomere Structure.

29. Skeletal Muscle Fibers Figure 10–4b Sarcomere Structure.

30. Skeletal Muscle Fibers Figure 10–5 Sarcomere Structure.

31. Skeletal Muscle Fibers Figure 10–6 Levels of Functional Organization in a Skeletal Muscle.

32. Skeletal Muscle Fibers Figure 10–6 Levels of Functional Organization in a Skeletal Muscle.

33. Skeletal Muscle Fibers  Sarcomere Function  Transverse tubules encircle the sarcomere near zones of overlap  Ca 2+ released by SR causes thin and thick filaments to interact

34. Skeletal Muscle Fibers  Muscle Contraction  Is caused by interactions of thick and thin filaments  Structures of protein molecules determine interactions

35. Skeletal Muscle Fibers  Four Thin Filament Proteins  F-actin (Filamentous actin)  Is two twisted rows of globular G-actin  The active sites on G-actin strands bind to myosin  Nebulin  Holds F-actin strands together  Tropomyosin  Is a double strand  Prevents actin–myosin interaction  Troponin  A globular protein  Binds tropomyosin to G-actin  Controlled by Ca 2+

36. Skeletal Muscle Fibers Figure 10–7a, b Thick and Thin Filaments.

37. Skeletal Muscle Fibers  Initiating Contraction  Ca 2+ binds to receptor on troponin molecule  Troponin–tropomyosin complex changes  Exposes active site of F-actin

38. Skeletal Muscle Fibers  Thick Filaments  Contain twisted myosin subunits  Contain titin strands that recoil after stretching  The mysosin molecule  Tail: –binds to other myosin molecules  Head: –made of two globular protein subunits –reaches the nearest thin filament

39. Skeletal Muscle Fibers Figure 10–7c, d Thick and Thin Filaments.

40. Skeletal Muscle Fibers  Myosin Action  During contraction, myosin heads  Interact with actin filaments, forming cross-bridges  Pivot, producing motion

41. Skeletal Muscle Fibers  Skeletal Muscle Contraction  Sliding filament theory  Thin filaments of sarcomere slide toward M line, alongside thick filaments  The width of A zone stays the same  Z lines move closer together

42. Skeletal Muscle Fibers Figure 10–8a Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber.

43. Skeletal Muscle Fibers Figure 10–8b Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber.

44. Skeletal Muscle Fibers  Skeletal Muscle Contraction  The process of contraction  Neural stimulation of sarcolemma: –causes excitation–contraction coupling  Cisternae of SR release Ca 2+ : –which triggers interaction of thick and thin filaments –consuming ATP and producing tension

45. The Neuromuscular Junction  Is the location of neural stimulation  Action potential (electrical signal)  Travels along nerve axon  Ends at synaptic terminal  Synaptic terminal: –releases neurotransmitter (acetylcholine or ACh) –into the synaptic cleft (gap between synaptic terminal and motor end plate)

46. The Neuromuscular Junction Figure 10–10a, b Skeletal Muscle Innervation.

47. The Neuromuscular Junction Figure 10–10c Skeletal Muscle Innervation.

48. The Neuromuscular Junction Figure 10–10c Skeletal Muscle Innervation.

49. The Neuromuscular Junction  The Neurotransmitter  Acetylcholine or ACh  Travels across the synaptic cleft  Binds to membrane receptors on sarcolemma (motor end plate)  Causes sodium–ion rush into sarcoplasm  Is quickly broken down by enzyme (acetylcholinesterase or AChE)

50. The Neuromuscular Junction Figure 10–10c Skeletal Muscle Innervation.

51. The Neuromuscular Junction  Action Potential  Generated by increase in sodium ions in sarcolemma  Travels along the T tubules  Leads to excitation–contraction coupling  Excitation–contraction coupling: –action potential reaches a triad: »releasing Ca 2+ »triggering contraction –requires myosin heads to be in “cocked” position: »loaded by ATP energy Show video neuromuscular junction

52. The Neuromuscular Junction Figure 10–11 The Exposure of Active Sites.

53. The Contraction Cycle  Five Steps of the Contraction Cycle  Exposure of active sites  Formation of cross-bridges  Pivoting of myosin heads  Detachment of cross-bridges  Reactivation of myosin

54. The Contraction Cycle Figure 10–12 The Contraction Cycle.

55. The Contraction Cycle [INSERT FIG. 10.12, step 1] Figure 10–12 The Contraction Cycle.

56. The Contraction Cycle Figure 10–12 The Contraction Cycle.

57. The Contraction Cycle Figure 10–12 The Contraction Cycle.

58. The Contraction Cycle Figure 10–12 The Contraction Cycle.

59. The Contraction Cycle Figure 10–12 The Contraction Cycle.

60. The Contraction Cycle  Fiber Shortening  As sarcomeres shorten, muscle pulls together, producing tension  Contraction Duration  Depends on  Duration of neural stimulus  Number of free calcium ions in sarcoplasm  Availability of ATP

61. The Contraction Cycle Figure 10–13 Shortening during a Contraction.

62. The Contraction Cycle  Relaxation  Ca 2+ concentrations fall  Ca 2+ detaches from troponin  Active sites are re-covered by tropomyosin  Sarcomeres remain contracted  Rigor Mortis  A fixed muscular contraction after death  Caused when  Ion pumps cease to function; ran out of ATP  Calcium builds up in the sarcoplasm

63. The Contraction Cycle

64. Tension Production  The all–or–none principle  As a whole, a muscle fiber is either contracted or relaxed  Tension of a Single Muscle Fiber  Depends on  The number of pivoting cross-bridges  The fiber’s resting length at the time of stimulation  The frequency of stimulation  Need more force? Recruit more fibers

65. Tension Production  Tension of a Single Muscle Fiber  Length–tension relationship  Number of pivoting cross-bridges depends on: –amount of overlap between thick and thin fibers  Optimum overlap produces greatest amount of tension: –too much or too little reduces efficiency  Normal resting sarcomere length: –is 75% to 130% of optimal length

66. Tension Production Figure 10–14 The Effect of Sarcomere Length on Active Tension.

67. Tension Production  Tension of a Single Muscle Fiber  Frequency of stimulation  A single neural stimulation produces: –a single contraction or twitch –which lasts about 7–100 msec.  Sustained muscular contractions: –require many repeated stimuli

68. Tension Production  Three Phases of Twitch  Latent period before contraction  The action potential moves through sarcolemma  Causing Ca 2+ release  Contraction phase  Calcium ions bind  Tension builds to peak  Relaxation phase  Ca 2+ levels fall  Active sites are covered  Tension falls to resting levels

69. Control of Muscle Tension

70. Tension Production Figure 10–15 The Development of Tension in a Twitch.

71. Tension Production Figure 10–15 The Development of Tension in a Twitch.

72. Tension Production  Treppe  A stair-step increase in twitch tension  Repeated stimulations immediately after relaxation phase  Stimulus frequency <50/second  Causes a series of contractions with increasing tension

73. Tension Production  Tension of a Single Muscle Fiber  Wave summation  Increasing tension or summation of twitches  Repeated stimulations before the end of relaxation phase: –stimulus frequency >50/second  Causes increasing tension or summation of twitches

74. Tension Production  Tension of a Single Muscle Fiber  Incomplete tetanus  Twitches reach maximum tension  If rapid stimulation continues and muscle is not allowed to relax, twitches reach maximum level of tension  Complete Tetanus  If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction

75. Tension Production Figure 10–16 Effects of Repeated Stimulations.

76. Tension Production Figure 10–16 Effects of Repeated Stimulations.

77. Tension Production  Tension Produced by Whole Skeletal Muscles  Depends on  Internal tension produced by muscle fibers  External tension exerted by muscle fibers on elastic extracellular fibers  Total number of muscle fibers stimulated

78. Tension Production  Tension Produced by Whole Skeletal Muscles  Motor units in a skeletal muscle  Contain hundreds of muscle fibers  That contract at the same time  Controlled by a single motor neuron

79. Tension Production  Tension Produced by Whole Skeletal Muscles  Recruitment (multiple motor unit summation)  In a whole muscle or group of muscles, smooth motion and increasing tension are produced by slowly increasing the size or number of motor units stimulated  Maximum tension  Achieved when all motor units reach tetanus  Can be sustained only a very short time

80. Tension Production Figure 10–17 The Arrangement and Activity of Motor Units in a Skeletal Muscle.

81. Tension Production Figure 10–17 The Arrangement and Activity of Motor Units in a Skeletal Muscle.

82. Tension Production  Tension Produced by Whole Skeletal Muscles  Sustained tension  Less than maximum tension  Allows motor units rest in rotation  Muscle tone  The normal tension and firmness of a muscle at rest  Muscle units actively maintain body position, without motion  Increasing muscle tone increases metabolic energy used, even at rest

83. Tension Production  Two Types of Skeletal Muscle Tension  Isotonic contraction  Isometric contraction

84. Tension Production  Two Types of Skeletal Muscle Tension  Isotonic Contraction  Skeletal muscle changes length: –resulting in motion  If muscle tension > load (resistance): –muscle shortens (concentric contraction)  If muscle tension < load (resistance): –muscle lengthens (eccentric contraction)

85. Tension Production  Two Types of Skeletal Muscle Tension  Isometric contraction  Skeletal muscle develops tension, but is prevented from changing length Note: iso- = same, metric = measure

86. Tension Production Figure 10–18a, b Isotonic and Isometric Contractions.

87. Tension Production Figure 10–18c, d Isotonic and Isometric Contractions.

88. Tension Production  Resistance and Speed of Contraction  Are inversely related  The heavier the load (resistance) on a muscle  The longer it takes for shortening to begin  And the less the muscle will shorten  Muscle Relaxation  After contraction, a muscle fiber returns to resting length by  Elastic forces  Opposing muscle contractions  Gravity

89. Tension Production Figure 10–19 Load and Speed of Contraction.

90. Tension Production  Elastic Forces  The pull of elastic elements (tendons and ligaments)  Expands the sarcomeres to resting length  Opposing Muscle Contractions  Reverse the direction of the original motion  Are the work of opposing skeletal muscle pairs

91. Tension Production  Gravity  Can take the place of opposing muscle contraction to return a muscle to its resting state

92. ATP and Muscle Contraction  Sustained muscle contraction uses a lot of ATP energy  Muscles store enough energy to start contraction  Muscle fibers must manufacture more ATP as needed

93. ATP and Muscle Contraction  ATP and CP Reserves  Adenosine triphosphate (ATP)  The active energy molecule  Creatine phosphate (CP)  The storage molecule for excess ATP energy in resting muscle  Energy recharges ADP to ATP  Using the enzyme creatine phosphokinase (CPK or CK)  When CP is used up, other mechanisms generate ATP

94. ATP and Muscle Contraction  Energy Use and Muscle Activity  At peak exertion  Muscles lack oxygen to support mitochondria  Muscles rely on glycolysis for ATP  Pyruvic acid builds up, is converted to lactic acid

95. ATP and Muscle Contraction Figure 10–20 Muscle Metabolism.

96. ATP and Muscle Contraction Figure 10–20a Muscle Metabolism.

97. ATP and Muscle Contraction Figure 10–20c Muscle Metabolism.

98. ATP and Muscle Contraction  Muscle Fatigue  When muscles can no longer perform a required activity, they are fatigued  Results of Muscle Fatigue  Depletion of metabolic reserves  Damage to sarcolemma and sarcoplasmic reticulum  Low pH (lactic acid)  Muscle exhaustion and pain

99. ATP and Muscle Contraction  The Cori Cycle  The removal and recycling of lactic acid by the liver  Liver converts lactic acid to pyruvic acid  Glucose is released to recharge muscle glycogen reserves  Oxygen Debt  After exercise or other exertion  The body needs more oxygen than usual to normalize metabolic activities  Resulting in heavy breathing

100. ATP and Muscle Contraction  Skeletal muscles at rest metabolize fatty acids and store glycogen  During light activity, muscles generate ATP through anaerobic breakdown of carbohydrates, lipids, or amino acids  At peak activity, energy is provided by anaerobic reactions that generate lactic acid as a byproduct

101. ATP and Muscle Contraction  Muscle Performance  Power  The maximum amount of tension produced  Endurance  The amount of time an activity can be sustained  Power and endurance depend on  The types of muscle fibers  Physical conditioning

102. Muscle Fiber Types  Three Types of Skeletal Muscle Fibers  Fast fibers  Slow fibers  Intermediate fibers

103. Muscle Fiber Types  Three Types of Skeletal Muscle Fibers  Fast fibers  Contract very quickly  Have large diameter, large glycogen reserves, few mitochondria  Have strong contractions, fatigue quickly

104. Muscle Fiber Types  Three Types of Skeletal Muscle Fibers  Slow fibers  Are slow to contract, slow to fatigue  Have small diameter, more mitochondria  Have high oxygen supply  Contain myoglobin (red pigment, binds oxygen)

105. Muscle Fiber Types  Three Types of Skeletal Muscle Fibers  Intermediate fibers  Are mid-sized  Have low myoglobin  Have more capillaries than fast fibers, slower to fatigue

106. Muscle Fiber Types Figure 10–21 Fast versus Slow Fibers.

107. Muscle Fiber Types  Muscles and Fiber Types  White muscle  Mostly fast fibers (aka Fast twitch)  Pale ( e.g., chicken breast)  Red muscle  Mostly slow fibers (aka slow twitch)  Dark ( e.g., chicken legs)  Most human muscles  Mixed fibers (General proportions determined by genetics)  Pink

108. Muscle Fiber Types  Muscle Hypertrophy  Muscle growth from heavy training  Increases diameter of muscle fibers  Increases number of myofibrils  Increases mitochondria, glycogen reserves  Muscle Atrophy  Lack of muscle activity  Reduces muscle size, tone, and power

109. Muscle Fiber Types  What you don’t use, you lose  Muscle tone indicates base activity in motor units of skeletal muscles  Muscles become flaccid when inactive for days or weeks  Muscle fibers break down proteins, become smaller and weaker  With prolonged inactivity, fibrous tissue may replace muscle fibers