Structure and Function of the Musculoskeletal System

1. Structure and Function of the Musculoskeletal System Chapter 36

2. Skeletal System Forms the body Supports tissues Permits movement by providing points of attachment for muscles Site of blood cell formation Mineral storage

3. Elements of Bone Tissue Rigid connective tissue Constituents: Cells Fibers Ground substance Calcium

4. Bone Cells Enable bone to grow, repair, synthesize new bone tissue and resorb old tissue Osteoblasts Derived from mesenchymal stromal cells Produce type I collagen Respond to parathyroid hormone Produce osteocalcin Synthesize osteoid Nonmineralized bone matrix

5. Bone Tissue Osteoclasts The major reabsorptive cells of the bone Large, multinucleated cells Contain lysosomes filled with hydrolytic enzymes Osteocytes Transformed osteoblast that are surrounded in osteoid as it hardens from deposited minerals Synthesize matrix molecules for bone calcification

6. Bone Cells

7. Bone Matrix Collagen fibers Make up bulk of bone matrix Proteoglycans Strengthen bone and assist bone calcium deposition

8. Bone Matrix (cont’d) Glycoproteins Sialoprotein, osteocalcin, bone albumin, alpha-glycoprotein Control collagen interactions that lead to fibril formation Bone mineralization Calcium and phosphate

9. Bone Tissue Compact (cortical) bone 85% of the skeleton Haversian system Haversian canal, lamellae, lacunae, osteocyte, and canaliculi Spongy (cancellous) bone Lack haversian systems Trabeculae Periosteum

10. Bone Tissue (cont’d)

11. Bone 206 bones Axial skeleton 80 bones Skull Vertebral column Thorax Appendicular skeleton 126 bones Upper and lower extremities Shoulder girdle Pelvic girdle

12. Skeleton

13. Bones Long bones Diaphysis Metaphysis Epiphysis Epiphyseal plate Medullary cavity Endosteum

14. Long Bone

15. Bones Flat bones Ribs Scapulae Short bones (cuboidal bones) Wrist Ankles Irregular bones Vertebrae Mandibles Facial bones

16. Bone Remodeling Basic multicellular units Repairs microscopic injuries and maintains bone integrity Three phases: Activation of the remodeling cycle Resorption Formation of new bone

17. Bone Remodeling (cont’d)

18. Bone Repair Inflammation/hematoma formation Procallus formation Callus formation Callus replacement Remodeling

19. Joints Site where two or more bones meet Promote stability and mobility to the skeleton

20. Joints (cont’d) Joint classifications based on movement: Synarthrosis Immovable Amphiarthrosis Slightly movable Diarthrosis Freely movable

21. Joints (cont’d) Joint classifications based on structure: Fibrous Joins bone to bone Suture, syndesmosis, gomphosis Cartilaginous Symphysis and synchondrosis Synovial Uniaxial, biaxial, or multiaxial Joint capsule, synovial membrane, joint cavity, synovial fluid, articular cartilage

22. Joints (cont’d)

23. Joints (cont’d)

24. Joints (cont’d)

25. Joints (cont’d)

26. Skeletal Muscles Millions of individual muscle fibers that contract and relax to facilitate movement 75% water, 20% protein, 5% organic and inorganic compounds More than 600 in body 2 to 60 cm long Fusiform muscles Pennate muscles

27. Skeletal Muscles (cont’d)

28. Skeletal Muscles (cont’d) Whole muscle Fascia Epimysium Tendon Perimysium Fascicles Endomysium

29. Skeletal Muscles (cont’d)

30. Muscle Skeletal muscle Voluntary Striated Extrafusal Motor unit Lower motor neurons Innervation ratios Sensory receptors Spindles Golgi tendon organs

31. Motor Units

32. Muscle Fibers Myofibrils Myoblasts White muscle (type II fibers) Red muscle (type I fibers) Muscle membrane Sarcolemma and basement membrane Sarcoplasm

33. Muscle Fibers (cont’d) Creatine and creatinine kinase Phosphate, chloride, calcium, magnesium, sodium, potassium

34. Muscle Fibers (cont’d) Sarcotubular system Transverse tubules Sarcoplasmic reticulum Sarcomere (myofibrils) Muscle proteins: Actin Myosin Troponin-tropomyosin complex

35. Myofibrils

36. Muscle Contraction Excitation Muscle fiber action potential Coupling Contraction Cross-bridge theory Relaxation

37. Muscle Metabolism Requires constant supply of ATP and phosphocreatine Strenuous activity requires oxygen Type I fibers can resist fatigue longer than type II fibers

38. Muscle Mechanics Repetitive discharge Allows the muscle to activate the number of motor units needed to generate the desired force Physiologic tetanus Increased strength, speed and duration of stimulation causes contractions to reach a critical frequency

39. Muscle Contractions and Movement Types of muscle contractions: Isometric contraction Isotonic contraction Eccentric Concentric Muscle movement Agonist Antagonist

40. Isotonic Contraction

41. Isometric Contraction

42. Ligaments and Tendons Ligaments Attach bone to bone Stabilize joints against excessive movement Tendons Attach muscle to bone Transfer forces from muscle to bone Act as a type of biological spring for muscles to allow additional stability during movement

43. Aging and the Musculoskeletal System Bones Bone loss Stiff, brittle, decreased strength Bone remodel time is lengthened Joints Cartilage becomes more rigid, fragile, stiff Decreased range of motion

44. Aging and the Musculoskeletal System (cont’d) Muscles Sarcopenia Decrease in muscle strength and bulk Reduced oxygen intake, basal metabolic rate, and lean body mass