1. Muscle Physiology

2. Energy for Physical Activity  Muscle function transforms chemical energy (ATP) into mechanical motion

3. Muscular System Functions  Body movement  Maintenance of posture  Respiration  Production of body heat  Communication  Constriction of organs and vessels  Heart beat

4. Properties of Muscle  Contractility  Ability of a muscle to shorten with force  Excitability  Capacity of muscle to respond to a stimulus  Extensibility  Muscle can be stretched to its normal resting length and beyond to a limited degree  Elasticity  Ability of muscle to recoil to original resting length after stretched

5. Muscle Tissue Types  Skeletal Muscle  Cardiac Muscle  Smooth Muscle

6. Skeletal Muscle  Long cylindrical cells  Many nuclei per cell  Striated  Voluntary  Rapid contractions

7. Cardiac Muscle  Branching cells  One or two nuclei per cell  Striated  Involuntary  Medium speed contractions

8. Smooth Muscle  Fusiform cells  One nucleus per cell  Nonstriated  Involuntary  Slow, wave-like contractions

9. Skeletal Muscle Structure  Muscle fibers or cells  Develop from myoblasts  Numbers remain constant  Connective tissue  Nerve and blood vessels

10. Microanatomy of Skeletal Muscle

12. Z line

16. H Band

17. Structure of Actin and Myosin

18. Sarcomere Relaxed

19. Sarcomere Partially Contracted

21. Binding Site Tropomyosin Troponin

22. Myosin

24. Mechanism of muscle contraction

26. Length-Tension diagram in a sarcomere

27. Length-Tension of a muscle

28. Physiology of Skeletal Muscle  Nervous system  Controls muscle contractions through action potentials  Resting membrane potentials  Membrane voltage difference across membranes (polarized) Inside cell more negative and more K +  Outside cell more positive and more Na +  Must exist for action potential to occur

29. Neuromuscular Junction

30. Next slide Motor neurone Motor axon Neuromuscular junction (motor nerve terminal) Skeletal muscle fibre

33. Acetylcholine Opens Na + Channel

35. Function of Neuromuscular Junction

36. Motor end plate potentials

37. Excitation-contraction coupling in the muscle

38. Action Potentials and Muscle Contraction

39. Transverse tubule - Sarcoplasmic Reticulum System

41. Muscle Contraction Summary  Nerve impulse reaches myoneural junction  Acetylcholine is released from motor neuron  Ach binds with receptors in the muscle membrane to allow sodium to enter  Sodium influx will generate an action potential in the sarcolemma

42. Muscle Contraction Continued  Action potential travels down T tubule  Sarcoplamic reticulum releases calcium  Calcium binds with troponin to move the troponin, tropomyosin complex  Binding sites in the actin filament are exposed

43. Muscle Contraction Continued  Myosin head attach to binding sites and create a power stroke  ATP detaches myosin heads and energizes them for another contaction  When action potentials cease the muscle stop contracting

44. Energetics of Muscle Contraction

45. Energy Sources  ATP provides immediate energy for muscle contractions from 3 sources  Creatine phosphate  During resting conditions stores energy to synthesize ATP (Creatine phosphate + ADP Creatine + ATP)  Anaerobic respiration  Occurs in absence of oxygen and results in breakdown of glucose to yield ATP and lactic acid  Aerobic respiration  Requires oxygen and breaks down glucose to produce ATP, carbon dioxide and water  More efficient than anaerobic

49. Characteristics of whole muscle contraction

50. Muscle Twitch  Muscle contraction in response to a stimulus that causes action potential in one or more muscle fibers  Phases  Lag or latent  Contraction  Relaxation

51. Types of Muscle Contractions  Isometric: No change in length but tension increases  Postural muscles of body  Isotonic: Change in length but tension constant  Concentric: Overcomes opposing resistance and muscle shortens  Eccentric: Tension maintained but muscle lengthens  Muscle tone: Constant tension by muscles for long periods of time

52. Isometric Contraction  Produces no movement  Used in  Standing  Sitting  Posture

54. Isotonic Contraction  Produces movement  Used in  Walking  Moving any part of the body

56. Duration of isometric contractions for different types of skeletal muscles

57. Slow and Fast Fibers  Slow-twitch or high-oxidative  Contract more slowly, smaller in diameter, better blood supply, more mitochondria, more fatigue- resistant than fast-twitch  Fast-twitch or low-oxidative  Respond rapidly to nervous stimulation, contain myosin to break down ATP more rapidly, less blood supply, fewer and smaller mitochondria than slow- twitch  Distribution of fast-twitch and slow twitch  Most muscles have both but varies for each muscle  Effects of exercise  Hypertrophies: Increases in muscle size  Atrophies: Decreases in muscle size

58. Slow and Fast Fibers:

61. Mechanics of Skeletal Muscle Contraction

62. Next slide Motor unit = Motor neurone Motor axon + branches + terminals All muscle fibres to which it connects One motor neurone has exclusive Control of many muscle fibres eg 10 oculomotor, 1000 biceps One muscle fibre innervated by one motor nerve terminal Motor neurone Motor axon Skeletal muscle fibre

63. Motor Unit All the muscle cells controlled by one nerve cell

64. Motor Unit Ratios  Back muscles  1:100  Finger muscles  1:10  Eye muscles  1:1

65. Muscle Contractions of different Force – Force Summation

66. Multiple Motor Unit Summation  A whole muscle contracts with a small or large force depending on number of motor units stimulated to contract

67. Multiple-Wave Summation  As frequency of action potentials increase, frequency of contraction increases  Action potentials come close enough together so that the muscle does not have time to completely relax between contractions.

68. Frequency Summation and Tetanization  Incomplete tetanus  Muscle fibers partially relax between contraction  There is time for Ca 2+ to be recycled through the SR between action potentials

69.  Complete tetanus  No relaxation between contractions  Action potentials come sp close together that Ca 2+ does not get re- sequestered in the SR

70. Refractory Period  Brief period of time in which muscle cells will not respond to a stimulus

71. Refractory

72. Skeletal MuscleCardiac Muscle Refractory Periods

73. Treppe  Graded response  Occurs in muscle rested for prolonged period  Each subsequent contraction is stronger than previous until all equal after few stimuli

74. Muscle Tonus  Tightness of a muscle  Some fibers always contracted

75. Fatigue  Decreased capacity to work and reduced efficiency of performance  Types:  Psychological  Depends on emotional state of individual  Muscular  Results from ATP depletion  Synaptic  Occurs in neuromuscular junction due to lack of acetylcholine

76. Remodelling of Muscle to Match Function

77. Muscle Hypertrophy  Enlargement of a muscle  More capillaries  More mitochondria  Caused by  Strenuous exercise  Steroid hormones: Stimulate muscle growth and hypertrophy

78. Muscle Atrophy  Weakening and shrinking of a muscle  May be caused  Immobilization  Loss of neural stimulation

79. Effects of Aging on Skeletal Muscle  Reduced muscle mass  Increased time for muscle to contract in response to nervous stimuli  Reduced stamina  Increased recovery time  Loss of muscle fibers  Decreased density of capillaries in muscle

80. Smooth Muscle  Characteristics  Not striated  Dense bodies instead of Z disks as in skeletal muscle  Have noncontractile intermediate filaments  Ca 2+ required to initiate contractions

83. Smooth Muscle Types  Visceral or unitary  Function as a unit  Multiunit  Cells or groups of cells act as independent units

84. Multi-unit and unitary smooth muscle

85. Electrical Properties of Smooth Muscle

86. Action potentials in smooth muscle

88. Sarcoplasmic tubules in a smooth muscle fiber

89. Smooth Muscle Contraction

90. Innervation of Smooth muscle

91. Functional Properties of Smooth Muscle  Some visceral muscle exhibits autorhythmic contractions  Tends to contract in response to sudden stretch but no to slow increase in length  Exhibits relatively constant tension: Smooth muscle tone  Amplitude of contraction remains constant although muscle length varies

92. Smooth Muscle Regulation  Innervated by autonomic nervous system  Neurotransmitter are acetylcholine and norepinephrine  Hormones important as epinephrine and oxytocin  Receptors present on plasma membrane which neurotransmitters or hormones bind determines response

93. THE END