The Musculoskeletal System. Chapter 46

Transcription

1 The Musculoskeletal System Chapter 46

2 Types of Skeletal Systems Changes in movement occur because muscles pull against a support structure Zoologists recognize three types: 1. Hydrostatic skeletons a fluid filled cavity, coelom, surrounded by muscle 2. Exoskeletons 3. Endoskeletons 2

3 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 3

4 Endoskeletons Rigid internal skeletons that form the body s framework and offer surfaces for muscle attachment Vertebrate bone is made of calcium phosphate 4

5 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 5

6 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Exoskeleton Exoskeleton a. Chitinous outer covering Sagittal section Endoskeleton Skull Ribs Vertebral column axial skeleton appendicular skeleton Pelvis Scapula Humerus Radius Ulna Femur Tibia Fibula b. 6

7 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 7

8 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Epiphysis Red marrow in spongy bone Growth plate Compact bone Medullary cavity Haversian system Capillary in Haversian canal Outer layers Shaft Compact transition to medullary bone Lacunae containing osteocytes Periosteum (osteoblasts found here) Sharpey s fibers Medullary bone Epiphysis Medullary cavity Canaliculi Lamellae 8

9 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 9

10 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 10

11 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ball-and-Socket Hinge Joint Gliding Joint a. b. c. Combination Joint d. 11

12 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 12

13 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Flexion Flexors (hamstrings) Tendon 13

14 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Flexion Flexors (hamstrings) Tendon Extension Tendon Extensors (quadriceps) 14

15 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 15

16 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tendon The organization of vertebrate skeletal muscle Bundle of muscle fibers Plasma membrane Myofibril Skeletal muscle Nuclei Muscle fiber (cell) Myofilaments Striations 16

17 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 17

18 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Relaxed Muscle Sarcomere Sarcomere Z line A band H band I band A band H band Z line A band H band I band A band H band Z line Thin filaments (actin) Thick filaments (myosin) Dr. H.E. Huxley 0.49 µm 18

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20 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 20

21 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Contracted Muscle Sarcomere Sarcomere Z line A band H band I band A band H band Z line Z line Dr. H.E. Huxley 0.45 µm 21

22 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 22

23 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Myosin Molecule Myosin head a. Thick Filament Myosin head b. Thin filament Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tropomyosin Actin molecules Troponin 23

24 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 24

25 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sarcomere Z line A band H band I band a. Thin filaments (actin) Cross-bridges Thick filament (myosin) b. 25

26 c. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Actin Myosin binding site ATP hydrolysis P i ADP Cross-bridge formation Myosin head Cross-bridge a. ATP d. b. ATP binding, actin release Power stroke 26

27 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 27

28 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 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Troponin Tropomyosin Binding sites for cross-bridges blocked Binding sites for cross-bridges exposed Actin Ca 2+ Myosin head Myosin a. b. 28

29 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 29

30 Skeletal Muscle Contraction Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Motor neuron Nerve impulse Neurotransmitter Muscle depolarization Neuromuscular junction Sarcolemma Na + Myofibril Sarcoplasmic reticulum Transverse tubule (T tubule) Ca 2+ Release of Ca 2+ 30

31 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 31

32 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fewer Motor Units Activated More Motor Units Activated Motor unit Muscle fiber Tapping Toe Running a. b. 32

33 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 33

34 Amplitude of Muscle Contractions Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Complete tetanus Summation Incomplete tetanus Twitches Stimuli Time 34

35 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 35

36 Contraction Strength 2 Types of Muscle Fibers Skeletal muscles have different proportions of fast-twitch and slow-twitch fibers Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Eye muscle (lateral rectus) Calf muscle (gastrocnemius) Deep muscle of leg (soleus) Time (msec) 36

37 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 37