1. The Muscular System

2. A.Function of Muscles Muscles are responsible for four functions 1. P roduce movement Contraction! Skeletal: Run away from danger, smile in flirtation Smooth: peristalsis of digestion Cardiac: beat of heart 2. M aintain posture Upright/seated – fight downward pull of gravity

3. 3. S tabilize joints Tendons attaching muscles to bones of joints for stabilization

4. 4. Generate heat By-product of muscle activity produces heat As ATP (adenosine triphosphate) is used to power contraction, ¾ energy released as heat Maintains normal body temperature (homeostasis!) Skeletal muscle (40% body mass) most responsible

5. B.Types of Muscles Three basic muscle types are found in the body i. Skeletal muscle - attached to bones ii. Smooth muscle - hollow visceral (internal) organs iii. Cardiac muscle – heart

7. i.Skeletal Muscles Most are attached by tendons to bones Cells are multinucleate (many nuclei in one cell) Striated – have visible banding Voluntary – subject to conscious control Cells are surrounded and bundled by connective tissue

8. Muscle fiber = muscle cell Endomysium – around single muscle fiber Fascicle = bundle of fibers Perimysium – around a fascicle Typical skeletal muscle = bundle of fascicles Epimysium – covers the entire skeletal muscle Fascia – on the outside of the epimysium Figure 6.1 “Packaging” of Skeletal Muscles

9. Epimysium blends into a connective tissue attachment Tendon – cord-like structure Aponeuroses – sheet-like structure Sites of muscle attachment Bones Cartilages Connective tissue coverings

10. ii.Smooth Muscle Has no striations Spindle-shaped cells Single nucleus Involuntary – no conscious control Found mainly in the walls of hollow organs Figure 6.2a

11. iii.Cardiac Muscle Has striations Usually has a single nucleus Joined to another muscle cell at an intercalated disc Involuntary Found only in the heart Figure 6.2b

13. C.Anatomy of Skeletal Muscle Cells are multinucleate (many nuclei per cell) Nuclei (oval-shaped) are just beneath the sarcolemma (specialized plasma membrane) Contain sarcoplasmic reticulum (specialized smooth endoplasmic reticulum [ER]) for Ca 2+ storage Figure 6.3a

14. One muscle fiber (muscle cell) is made of a bundle of myofibrils (organelles) that nearly fill cytoplasm

15. One myofibril (organelle) is made of chains of tiny contractile units called sarcomeres (Z disc to Z disc) SARCOMERE

16. one sarcomere is made of two myofilaments (protein filaments): actin (thin) and myosin (thick)

17. Thick filaments Composed of the protein myosin Has ATPase enzymes which break ATP bonds to make energy for muscle contraction! Thin filaments Composed of the protein actin Figure 6.3c

18. Myosin filaments have heads (extensions, or cross bridges which look like golf club heads) that move Myosin and actin overlap somewhat Figure 6.3d

19. RECAP Muscle fiber Myofibrils Sarcomere oMyofilaments Actin Myosin Site of muscle contraction

21. Figure 6.3b Alignment of myofibrils in sarcomere creates banding pattern I band (light band) = absence of myosin A band (dark band) = concentration of myosin

22. Z disc =Area where actin joins other actin molecules, forms Z-shaped pattern H zone (bare zone) = area that lacks thin filaments M line = center of H zone that contains tiny protein rods that hold adjacent myosin proteins together

23. Banding pattern changes shape during contraction when each sarcomere segment gets shortened (H zone gets smaller)

24. D.Muscle Activity: Contraction Muscle has two functional properties that are necessary for contraction: receive respond 1. Irritability – ability to receive and respond to a stimulus (nerve to muscle) shorten 2. Contractility – ability to shorten when an adequate stimulus is received via sliding filament theory (inside muscle)

25. 1.Irritation: Nerve Stimulus to Muscles Skeletal muscles must be stimulated by a nerve Motor units are responsible for stimulating a few to hundreds of muscle cells. Consist of One neuron All muscle cells stimulated by that one neuron Figure 6.4a

26. Neuron (nerve cell) relays message through electrical and chemical signals. Consists of Cell body (with dendrite fingers) Axon or nerve fiber (with axon terminal projections)

27. Axon terminals approach (never physically touch) muscle’s sarcolemma via neuromuscular junctions Gap between axon terminals and muscle cells called synaptic cleft Filled with interstitial (“between tissues”) fluid Figure 6.5b

28. 1.Electrical nerve impulse reaches dendrites Steps of Nerve Stimulation

29. 2.Signal moves down cell body, to axon terminals, signals vesicles with chemical neurotransmitter called acetylcholine (ACh) to move to nerve membrane

30. 3.ACh is released via exocytosis into synaptic cleft (space between nerve and muscle) 4.ACh attaches to receptors on the sarcolemma membrane 5.Triggers Na + /K + (sodium/potassium) pumps to open, making sarcolemma permeable to Na + (Na + rushes in, K + rushes out)

31. 6.Rapid change in ion movement (sodium in, potassium out of the cell) is called depolarization which generates an electrical current called action potential 7.Action potential will start, muscle contraction which cannot be stopped travels over entire surface of sarcolemma

32. In the meantime, ACh is now broken down by enzyme (AChase) to acetic acid and choline This is why one nerve impulse produces one contraction

33. Steps of Nerve Stimulation 1.Nerve cell receives electrical stimulus through dendrites 2.Stimulus send down cell body, out through axon terminals as chemical signal 3.ACh neurotransmitter released from vesicles into synaptic cleft 4.Receptors on sarcolemma receive ACh 5.Sarcolemma now permeable to Na + ions = Na + rushes in, K + rushes out 6.Depolarization of muscle cells creates action potential

34. 2.Contraction: The Sliding Filament Theory Activation by nerve causes myosin heads (cross bridges) to attach to binding sites on the thin (actin) filament Myosin heads then bind to the next site of the thin filament due to Ca 2+ and ATP Figure 6.7

35. Ca 2+ from sarcoplasmic reticulum which was triggered to release Ca 2+ as a result of action potential This continued action causes a sliding of the myosin along the actin The result is that the muscle is shortened (contracted) Figure 6.7

37. Figure 6.8

41. Muscle cell relaxes again when: 1. diffusion of K+ ions out of cell 2. Na+/K+ pump brings ions back to original state (Na+ back out, K+ back in)

42. 1.Action potential triggers sarcoplasmic reticulum to release Ca2+ 2.Action potential causes myosin heads to attach to binding sites on actin filament 3.Ca2+ with ATP triggers myosin heads to attach to neighbor binding sites on same actin filament, causing actin to move toward each other = contraction! Sliding Filament Contraction Recap

43. Muscle fiber contraction is “all or none” Within a skeletal muscle, not all fibers may be stimulated during the same interval Different combinations of muscle fiber contractions may give differing responses Graded responses – different degrees of skeletal muscle shortening Contraction Responses

44. Types of Graded Responses 1. Twitch Single, brief contraction Not a normal muscle function Figure 6.9a–b

45. 2. Tetanus (summing of contractions) One contraction is immediately followed by another The muscle does not completely return to a resting state The effects are added (summed) Figure 6.9a–b

46. 3. Fused (complete) tetanus No evidence of relaxation before the following contractions The result is a sustained muscle contraction Figure 6.9c–d

47. Muscle force depends upon the number of fibers stimulated More fibers contracting results in greater muscle tension Muscles can continue to contract unless they run out of energy

48. Muscle Fatigue and Oxygen Debt When a muscle is fatigued, it is unable to contract The common reason for muscle fatigue is oxygen debt Oxygen must be “repaid” to tissue to remove oxygen debt Oxygen is required to get rid of accumulated lactic acid Breathing heavy! Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less

49. Types of Muscle Contractions Isotonic contractions Myofilaments are able to slide past each other during contractions The muscle shortens (movement) Ex: bending knee, smiling Isometric contractions Tension in the muscles increases The muscle is unable to shorten (no movement) Ex: lifting 400-lb table alone, push against wall

50. Muscle Tone Some fibers are contracted even in a relaxed muscle Different fibers contract at different times to provide muscle tone The process of stimulating various fibers is under involuntary control

51. E.Body Movements Movement is attained due to a muscle moving an attached bone Muscles are attached to at least two points Insertion – attachment to a moveable bone Origin– attachment to an immovable bone Figure 6.12

52. Ordinary Body Movements Flexion – decreases angle of joint & brings two bones closer together Extension – opposite of flexion (increases angle, bones farther apart) Rotation – movement of bone around longitudinal axis Abduction – move AWAY from midline Adduction – move TOWARD midline Circumduction – proximal end of bone stationary, distal end moves in circle opposites

53. Figure 6.13a–c

55. Figure 6.13d

56. Special Movements Dorsiflexion – lifting foot so its superior surface approaches shin (decrease angle) Plantar flexion – pointing toes away from shin (increase angle) Retraction – moving bone slightly backward Protraction – moving bone slightly forward opposites

57. Inversion – move sole of foot up and inward Eversion – move sole of foot up and outward opposites

58. Supination – radius and ulna are parallel (palm up) Pronation – radius rotates over ulna (palm down) Opposition –thumb touching tip of other fingers opposites

59. F.Types of Muscles Prime mover (agonist) – muscle with the major responsibility for contracting Antagonist – muscle that opposes or reverses a prime mover (relaxes) Synergist – muscle that aids a prime mover in a movement and helps prevent rotation Fixator – stabilizes the origin of a prime mover Agonist vs. Antagonist Muscle

60. Naming of Skeletal Muscles Direction of muscle fibers Example: rectus (straight) Relative size of the muscle Example: maximus (largest)

61. Location of the muscle Example: many muscles are named for bones (e.g., temporalis)

62. Number of origins Example: triceps (three heads)

63. Location of the muscle’s origin and insertion Example: sterno (on the sternum) Shape of the muscle Example: deltoid (triangular)

64. Action of the muscle Example: flexor and extensor (flexes or extends a bone)

66. Head and Neck Muscles Figure 6.15

67. Trunk Muscles Figure 6.16

68. Deep Trunk and Arm Muscles Figure 6.17

69. Muscles of the Pelvis & Hip Figure 6.19c

70. Muscles of the Thigh

71. Muscles of the Lower Leg Figure 6.20

72. Muscles of the Arm

73. Muscles For Injections

74. Superficial Muscles: Anterior Figure 6.21

75. Superficial Muscles: Posterior Figure 6.22

76. G.Muscular Development In embryo, muscular system develops quickly Muscles have to cover and move bones of limbs Nervous system invades muscles to allow conscious control Skeletal movements occur by 16 th week of development Fetus will start moving around 14 th week Sucking thumb, tugging, kicking

77. Fetus at 16 weeks

78. Development occurs in: cephalic/caudal direction (head to toe) Can raise its head before it can sit up Can sit up before it can walk Proximal/distal direction Can wave “bye-bye” before it can hold a pencil

79. Due to rich blood supply, skeletal muscles are resistant to infection able to repair/regenerate selves very efficiently Aging will alter muscle ability and can lead to atrophy Amount of connective tissue increases, muscle tissue decreases Leads to stringy/sinewy muscles Leads to decreased body weight/mass Muscle strength decreases by about 50% by age 80 Continued or new dedication to weight-bearing exercise (pumping iron) will offset or reverse effects

80. Jack LaLanne, at age 83 (left), and 93 (right) Often referred to as the Godfather of Fitness, Jack Lalane was a pioneer in American fitness. He advocated healthy eating and daily weight training exercises starting in the 1930s.

81. H.Diseases/Homeostatic Imbalances Two major diseases affect muscles: Muscular dystrophy: genetic disease group in which muscles degenerate due to fat and connective tissue deposits Myasthenia gravis: autoimmune disease in adults of general weakness and fatigability as a result of shortage of ACh receptors

82. Muscular Dystrophy (MD) Nine different types of muscular dystrophy in which all are genetic and result in degeneration of voluntary and sometimes involuntary muscles Most common (and most serious) type is Duchenne’s MD X-linked (affects males almost always) Diagnosed between ages 2 – 6

83. Active, normal-appearing children become clumsy and begin to fall as muscles start to weaken First muscles stricken are around hips, pelvis, thighs, and shoulders By early teens, attacks involuntary muscles like heart and respiratory muscles

84. A group of interdependent proteins along the membrane surrounding each fiber helps to keep muscle cells working properly. When one of these proteins, dystrophin, is absent, the result is Duchenne muscular dystrophy; poor or inadequate dystrophin results in Becker muscular dystrophy.

85. Myasthenia Gravis (MG) Chronic autoimmune neuromuscular disease characterized by varying degrees of weakness of the skeletal (voluntary) muscles of the body. First signs are weakness in head and neck muscles droopy eyelids (orbicularis oculi), difficulty chewing (masseter), swallowing & talking May eventually lead to difficulty breathing

86. Result of shortage of ACh receptors available to receive ACh Antibodies bind to ACh receptors which prevent them from binding Ach Body thinks receptors are foreign body so produces antibodies to fight it off Receptors not triggered lead to weakened contractions

88. Test Wednesday, November 23 The End