1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 47 LECTURE SLIDES To run the animations you must be in Slideshow View. Use the buttons on the animation to play, pause, and turn audio/text on or off. Please note: once you have used any of the animation functions (such as Play or Pause), you must first click in the white background before you advance the next slide.

2. The Musculoskeletal System Chapter 47

3. Types of Skeletal Systems Changes in movement occur because muscles pull against a support structure Zoologists recognize three types: 1.Hydrostatic skeletons 2.Exoskeletons 3.Endoskeletons 3

4. Hydrostatic Skeletons Found primarily in soft-bodied invertebrates (terrestrial and aquatic) Locomotion in earthworms –Involves a fluid-filled central cavity (hydrostatic skeleton) and surrounding circular and longitudinal muscles –A wave of circular followed by longitudinal muscle contractions move fluid down body –Chaetae prevent slipping backward 4

5. 5 Hydrostatic Skeletons

6. Exoskeletons Surrounds the body as a rigid hard case Composed of chitin in arthropods Provides protection for internal organs and a site for muscle attachment Must be periodically shed in order for the animal to grow Not as strong as a bony skeleton Respiratory system sets limit on body size Muscles cannot enlarge in size and power 6

7. Endoskeletons Rigid internal skeletons that form the body’s framework and offer surfaces for muscle attachment Echinoderms have calcite skeletons –Made of calcium carbonate Vertebrate bone is made of calcium phosphate 7

8. Endoskeletons Vertebrate endoskeletons have bone and/or cartilage Bone is much stronger than cartilage, and much less flexible Unlike chitin, bone and cartilage are living tissues Can change and remodel in response to injury or physical stress 8

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10. Bone Bone is a hard but resilient connective tissue that is unique to vertebrates Bones can be classified by the two fundamental modes of development 1.Intramembranous development Bones form within a layer of connective tissue 2.Endochondral development Begin as tiny cartilaginous model 10

11. Bone Intramembranous development –Osteoblasts initiate bone development –Some cells become trapped in the bone matrix that they have produced –Change into osteocytes Reside in tight spaces called lacunae –The cells communicate through little canals termed canaliculi –Osteoclasts break down the bone matrix 11

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14. Bone Endochondral development –Typically bones that are deeper in the body –Begin as tiny cartilaginous models –Bone development consists of adding bone to the outside of a cartilaginous model, while replacing interior cartilage with bone –Calcification begins with the fibrous sheath, later called the periosteum –Trapped osteoblasts transform into osteocytes –Osteoclasts remodel bone 14

15. Bone Endochondral development –Increase in length unlike intramembranous bone –Limb bones have a shaft with epiphyses –Epiphyseal growth plates separate epiphyses from shaft –Plates are cartilage in growing bone –Growth pushes epiphysis away from shaft –Cartilage becomes calcified –Growth in length ends by late adolescence –Growth in width does not 15

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17. Bone Structure In most mammals, bones retain internal blood vessels and are called vascular bones –These typically have osteocytes and are also called cellular bones –Vascular bone has a special internal organization termed the Haversian system In birds and fishes, bones are avascular –Lack osteocytes and are also called acellular bones 17

18. Bone Structure Based on density and structure, bone falls into three categories 1.Compact bone – outer dense layer 2.Medullary bone – lines the internal cavity Contains bone marrow in vertebrates Bird bones are hollow 3.Spongy bone – forms the epiphyses inside a thick shell of compact bone 18

19. Bone Remodeling Bone is a dynamic tissue that can change Mechanical stress can remodel bone during embryonic development and on Bone may thicken Size and shape of surface features change in size and shape Large frequent forces can initiate remodeling Weight-lifting is one osteoporosis treatment 19

20. 20 Bone Remodeling

21. Joints (articulations) Locations where one bone meets another 4 basic joint movement patterns 1.Ball-and-socket joints – permit movement in all directions 2.Hinge joints – allow movement in only one plane 3.Gliding joints – permit sliding of one surface over another 4.Combination joints – movement characteristics of two or more joint types 21

22. 22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ball-and-Socket Combination Joint Hinge JointGliding Joint a. d. b.c.

23. Skeletal Muscle Movement Skeletal muscle fibers are attached to bones –Directly to the periosteum –Through a tendon attached to the periosteum One attachment of the muscle, the origin, remains stationary during contraction The other end, the insertion, is attached to a bone that moves when muscle contracts Muscles can be antagonistic –One counters the action of the other 23

24. 24 Flexion Flexors (hamstrings) Tendon Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

25. 25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Extension Flexion Flexors (hamstrings) Tendon Extensors (quadriceps)

26. Muscle contraction Each skeletal muscle contains numerous muscle fibers Each muscle fiber encloses a bundle of 4 to 20 elongated structures called myofibrils Each myofibril in turn is composed of thick and thin myofilaments Under a microscope, the myofibrils have alternating dark and light bands – striated 26

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28. A bands – stacked thick and thin myofilaments –Dark bands –H band has interdigitating thick and thin filaments I bands – consist only of thin myofilaments –Light bands –Divided into two halves by a disc of protein called the Z line Sarcomere – distance between two Z lines –Smallest subunit of muscle contraction 28

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30. Skeletal Muscle Contraction Muscle contracts and shortens because the myofibrils contract and shorten –Myofilaments themselves do not shorten Instead, the thick and thin filaments slide relative to each other –Sliding filament mechanism Thin filaments slide deeper into the A bands, making the H and I bands narrower 30

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32. Skeletal Muscle Contraction Thick filament –Composed of several myosin subunits packed together –Myosin consists of two polypeptide chains wrapped around each other –Each chain ends with a globular head Thin filament –Composed of two chains of actin proteins twisted together in a helix 32

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34. Skeletal Muscle Contraction Cross-bridge cycle Hydrolysis of ATP by myosin activates the head for the later power stroke ADP and P i remain bound to the head, which binds to actin forming a cross-bridge During the power stroke, myosin returns to its original shape, releasing ADP and P i ATP binds to the head which releases actin 34

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37. Skeletal Muscle Contraction When a muscle is relaxed, its myosin heads cannot bind to actin because the attachment sites are blocked by tropomyosin In order for muscle to contract, tropomyosin must be removed by troponin This process is regulated by Ca 2+ levels in the muscle fiber cytoplasm 37

38. Skeletal Muscle Contraction In low Ca 2+ levels, tropomyosin inhibits cross-bridge formation In high Ca 2+ levels, Ca 2+ binds to troponin –Tropomyosin is displaced, allowing the formation of actin-myosin cross-bridges 38

39. Skeletal Muscle Contraction Muscle fiber is stimulated to contract by motor neurons, which secrete acetylcholine at the neuromuscular junction Membrane becomes depolarized Depolarization is conducted down the transverse tubules (T tubules) Stimulate the release of Ca 2+ from the sarcoplasmic reticulum (SR) Excitation–contraction coupling –Release of Ca 2+ that links excitation by motor neuron to contraction of the muscle 39

40. 40 Skeletal Muscle Contraction

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42. Skeletal Muscle Contraction Motor unit –Motor neuron and all of the muscle fibers it innervates –All fibers contract together when the motor neuron produces impulses Muscles that require precise control have smaller motor units –Muscles that require less precise control but exert more force, have larger motor units Recruitment is the cumulative increase in motor unit number and size leading to a stronger contraction 42

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44. 2 Types of Muscle Fibers A muscle stimulated with a single electric shock quickly contracts and relaxes in a response called a twitch Summation of closely spaced twitches Tetanus – sustained contraction with no relaxation between twitches Skeletal muscles divided on the basis of their contraction speed –Slow-twitch or type I fibers –Fast-twitch or type II fibers 44

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46. 2 Types of Muscle Fibers Slow-twitch or type I fibers –Rich in capillaries, mitochondria, and myoglobin (red fibers) –Sustain action for long periods of time Fast-twitch or type II fibers –Poor in capillaries, mitochondria, and myoglobin (white fibers) –Adapted to respire anaerobically –Adapted for rapid power generation 46

47. 2 Types of Muscle Fibers Skeletal muscles have different proportions of fast-twitch and slow-twitch fibers 47

48. Types of Muscle Fibers Skeletal muscles at rest obtain most of their energy from aerobic respiration of fatty acids During use, energy comes from glycogen and glucose Maximum rate of oxygen consumption in the body is called the aerobic capacity Muscle fatigue is the use-dependent decrease in the ability to generate force –Usually correlated with the production of lactic acid by the exercising muscle 48

49. Modes of Animal Locomotion Locomotion in large animals involves Appendicular locomotion –Produced by appendages that oscillate Axial locomotion –Produced by bodies that undulate, pulse, or undergo peristaltic waves The physical constraints to movement – gravity and frictional drag – occur in every environment, differing only in degree 49

50. Locomotion in Water Water’s buoyancy reduces effect of gravity Primary force retarding forward movement is frictional drag Some marine invertebrates move about using hydraulic propulsion All aquatic invertebrates swim –Swimming involves using the body or its appendages to push against the water –An eel uses its whole body –A trout uses only its posterior half 50

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52. Locomotion in Water Many terrestrial tetrapod vertebrates are able to swim, usually through limb movement Most birds that swim propel themselves by pushing against water with their hind legs –Typically have webbed feet Animals that swim with their forelegs usually have these modified as flippers and pull themselves through the water –Sea turtles and penguins 52

53. Locomotion on Land Terrestrial locomotion deals mainly with gravity Mollusks glide along a path of mucus Vertebrates and arthropods have a raised body, and move forward by pushing against the ground with jointed appendages – legs Vertebrates are tetrapods; all arthropods have at least six limbs –Having extra legs increases stability, but reduces the maximum speed 53

54. Locomotion on Land Basic walking pattern of quadrupeds generates a diagonal pattern of foot falls –Left hind leg, right foreleg, right hind leg, left foreleg –Allows running by a series of leaps Some vertebrates are also effective leapers –Kangaroos, rabbits, and frogs have powerful leg muscles 54

55. 55 Locomotion on Land

56. Locomotion in Air Flight has evolved among animals four times Insects, pterosaurs (extinct flying reptiles), birds, and bats –Convergent evolution All three vertebrate fliers modified the forelimb into a wing structure, but they did so in different ways –Birds have wing built on a single support –Bat wings built on multiple supports – finger bones 56

57. 57 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Polyphyletic Group b. BatPlatypusCrocodileDinosaursPterosaurHawk BatPterosaurHawk Flying Vertebrates GiraffeTurtle