The Skeletal System

1. The Skeletal System

2. The Skeletal System • Parts of the skeletal system • Bones (skeleton) • Joints • Cartilages • Ligaments • Two subdivisions of the skeleton • Axial skeleton • Appendicular skeleton

3. Functions of Bones • Support the body • Protect soft organs • Allow movement due to attached skeletal muscles • Store minerals and fats • Blood cell formation

4. Bones of the Human Body • The adult skeleton has 206 bones • Two basic types of bone tissue • Compact bone • Homogeneous • Spongy bone • Small needle-like pieces of bone • Many open spaces Figure 5.2b

5. Classification of Bones on the Basis of Shape Figure 5.1

6. Classification of Bones • Long bones • Typically longer than they are wide • Have a shaft with heads at both ends • Contain mostly compact bone • Example: • Femur • Humerus

7. Classification of Bones • Short bones • Generally cube-shape • Contain mostly spongy bone • Example: • Carpals • Tarsals

8. Classification of Bones • Flat bones • Thin, flattened, and usually curved • Two thin layers of compact bone surround a layer of spongy bone • Example: • Skull • Ribs • Sternum

9. Classification of Bones • Irregular bones • Irregular shape • Do not fit into other bone classification categories • Example: • Vertebrae • Hip bones

10. Anatomy of a Long Bone • Diaphysis • Shaft • Composed of compact bone • Epiphysis • Ends of the bone • Composed mostly of spongy bone

11. Anatomy of a Long Bone • Periosteum • Outside covering of the diaphysis • Fibrous connective tissue membrane • Sharpey’s fibers • Secure periosteum to underlying bone • Arteries • Supply bone cells with nutrients

12. Anatomy of a Long Bone • Articular cartilage • Covers the external surface of the epiphyses • Made of hyaline cartilage • Decreases friction at joint surfaces • Epiphyseal plate • Flat plate of hyaline cartilage seen in young, growing bone • Epiphyseal line • Remnant of the epiphyseal plate • Seen in adult bones

13. Anatomy of a Long Bone • Medullary cavity • Cavity inside of the shaft • Contains yellow marrow (mostly fat) in adults • Contains red marrow (for blood cell formation) in infants

14. Bone Markings • Surface features of bones • Sites of attachments for muscles, tendons, and ligaments • Passages for nerves and blood vessels • Categories of bone markings • Projections or processes—grow out from the bone surface • Depressions or cavities—indentations

15. Bone Markings Table 5.1 (1 of 2)

16. Bone Markings Table 5.1 (2 of 2)

17. Microscopic Anatomy of Bone • Osteon (Haversian system) • A unit of bone containing central canal and matrix rings • Central (Haversian) canal • Opening in the center of an osteon • Carries blood vessels and nerves • Perforating (Volkman’s) canal • Canal perpendicular to the central canal • Carries blood vessels and nerves

18. Microscopic Anatomy of Bone Figure 5.3a

19. Microscopic Anatomy of Bone • Lacunae • Cavities containing bone cells (osteocytes) • Arranged in concentric rings • Lamellae • Rings around the central canal • Sites of lacunae

20. Microscopic Anatomy of Bone • Canaliculi • Tiny canals • Radiate from the central canal to lacunae • Form a transport system connecting all bone cells to a nutrient supply

21. Formation of the Human Skeleton • In embryos, the skeleton is primarily hyaline cartilage • During development, much of this cartilage is replaced by bone • Cartilage remains in isolated areas • Bridge of the nose • Parts of ribs • Joints

22. Bone Growth (Ossification) • Epiphyseal plates allow for lengthwise growth of long bones during childhood • New cartilage is continuously formed • Older cartilage becomes ossified • Cartilage is broken down • Enclosed cartilage is digested away, opening up a medullary cavity • Bone replaces cartilage through the action of osteoblasts

23. Bone Growth (Ossification) • Bones are remodeled and lengthened until growth stops • Bones are remodeled in response to two factors • Blood calcium levels • Pull of gravity and muscles on the skeleton • Bones grow in width (called appositional growth)

24. Articularcartilage Hyalinecartilage Spongybone New center ofbone growth New boneforming Epiphysealplatecartilage Growthin bonewidth Medullarycavity Bone startingto replacecartilage Bloodvessels Growthin bonelength New boneforming Bone collar Epiphysealplate cartilage Hyalinecartilagemodel In an embryo In a fetus In a child (a) Long Bone Formation and Growth Figure 5.4a

25. Long Bone Formation and Growth Figure 5.4b

26. Types of Bone Cells • Osteocytes—mature bone cells • Osteoblasts—bone-forming cells • Osteoclasts—bone-destroying cells • Break down bone matrix for remodeling and release of calcium in response to parathyroid hormone • Bone remodeling is performed by both osteoblasts and osteoclasts

27. The Skeletal System: Fractures

28. Bone Fractures • Fracture—break in a bone • Types of bone fractures • Closed (simple) fracture—break that does not penetrate the skin • Open (compound) fracture—broken bone penetrates through the skin • Bone fractures are treated by reduction and immobilization

29. Common Types of Fractures Table 5.2

30. Hematoma Externalcallus Bonycallus ofspongybone Internalcallus(fibroustissue andcartilage) Newbloodvessels Healedfracture Spongybonetrabecula Bone remodeling Hematomaformation Fibrocartilagecallus formation Bony callusformation Repair of Bone Fractures • Hematoma (blood-filled swelling) is formed • Break is splinted by fibrocartilage to form a callus • Fibrocartilage callus is replaced by a bony callus • Bony callus is remodeled to form a permanent patch

31. The Axial Skeleton • Forms the longitudinal axis of the body • Divided into three parts • Skull • Vertebral column • Bony thorax

32. The Skull • Two sets of bones • Cranium • Facial bones • Bones are joined by sutures • Only the mandible is attached by a freely movable joint

33. Human Skull, Lateral View Figure 5.7

34. Human Skull, Superior View Figure 5.8

35. Human Skull, Inferior View Figure 5.9

36. Human Skull, Anterior View Figure 5.11

37. The Hyoid Bone • The only bone that does not articulate with another bone • Serves as a moveable base for the tongue • Aids in swallowing and speech

38. The Skeletal System: Fetal-Vertebrae

39. The Fetal Skull • The fetal skull is large compared to the infant’s total body length • Fontanels—fibrous membranes connecting the cranial bones • Allow the brain to grow • Convert to bone within 24 months after birth

40. The Fetal Skull Figure 5.13a

41. The Fetal Skull Figure 5.13b

42. The Vertebral Column • Each vertebrae is given a name according to its location • There are 24 single vertebral bones separated by intervertebral discs • Seven cervical vertebrae are in the neck • Twelve thoracic vertebrae are in the chest region • Five lumbar vertebrae are associated with the lower back

43. The Vertebral Column • Nine vertebrae fuse to form two composite bones • Sacrum • Coccyx

44. The Vertebral Column • The spine has a normal curvature • Primary curvatures are the spinal curvatures of the thoracic and sacral regions • Present from birth • Secondary curvatures are the spinal curvatures of the cervical and lumbar regions • Develop after birth

45. The Vertebral Column Figure 5.15

46. The Vertebral Column Figure 5.16

47. A Typical Vertebrae, Superior View Figure 5.17

48. Regional Characteristics of Vertebrae Figure 5.18a

49. Regional Characteristics of Vertebrae Figure 5.18b

50. Regional Characteristics of Vertebrae Figure 5.18c