The Skeletal System: Composition, Classification, and Functions

1. The Skeletal System

2. Chemical composition of bone Organic • Osteoblasts – bone-forming cells • Osteocytes – mature bone cells • Osteoclasts – large cells that reabsorb or break down bone matrix Inorganic • Mineral salts • Sixty-five percent of bone by mass • Mainly calcium phosphates • Responsible for bone hardness and its resistance to compression

3. Classification of Bones • 206 bones in the adult skeleton • composed of two basic kinds of osseous tissue that differ in their texture: • Compact bone • looks smooth and homogeneous • Spongy bone • Composed of small trabeculae of bone and lots of open space

4. Bones are further classified on the basis of their relative gross anatomy into four groups • Long bones • Femur • Are much longer then they are wide • Short bones • Carpals and tarsals • Are typically cube-shaped • Flat bones • Bones of the skull • Many are curved • Irregular bones • vertebrae • Bones that do not fall into one of the preceding categories.

5. Two other subcategories -Sesamoid bones • Kneecap • Are small bones formed in tendons • Wormian bones • Tiny bones between cranial bones

6. Five Major Functions • Support -structural framework • Protection -protects soft tissue/organs • Assistance in movement -provides surface for muscles to contract against • Storage of Mineral Salts -calcium and phosphate • Formation of blood cells -blood cell production

7. Long Bone Anatomy • Diaphysis = shaft • Thick collar of compact bone • Center = medullarycavity= bone marrow • Red bone marrow- produces blood cells, is found in the cavities of most bones. • Yellow bone marrow-fat storage.

8. Long Bone Anatomy • Epiphysis = distal and proximal end • Compact bone outside of spongy bone • Articular Cartilage covers the joint surface

9. Long Bone Anatomy • Metaphysis = where diaphysis and epiphysis meet • Contains epiphyseal plate (region of bone growth)

10. Long Bone • Articular Cartilage • Covers joint surface • Hyaline Cartilage • Reduces friction and absorbs shock

11. Long Bone Anatomy • Periosteum • Tough outer covering • (dense irregular connective tissue) surrounding bone.

12. Long Bone Anatomy • PeriosteumContains: • Lymph Vessels • Blood Vessels • Nerves • Provides site for tendon and ligament attachment • Allows for growth in Diameter NOT length • Assists in Fracture repair • Nourishment

13. Long Bone Anatomy • Endosteum • Lines the medullary cavity • Covers trabeculae-meshwork of spaces filled with bone marrow.

14. Terms to identify bone landmarks or surface features: • Process: A broad designation for any prominence or prolongation • Eminence: A raised area • Spine: An abrupt or pointed projection • Trochanter: A large, usually blunt process • Tubercle: A smaller, rounded eminence • Tuberosity: A large, often rough eminence • Crest: A prominent ridge

15. Basic terms continued • Head: A large, rounded, articular end of a bone; often set off from the shaft by a neck • Condyle: An oval articular prominence of a bone • Facet: A smooth, flat, or nearly flat articulating surface • Fossa: A deeper depression • Sulcus: A groove • Foramen: A hole • Meatus: A canal or opening to a canal

16. The Axial Skeleton • Divided into three parts: • Skull • Vertebral column • Bony thorax

17. SKULL • The skull is composed of two sets of bones: • Cranium bones • Encloses and protects the fragile brain • Facial bones • Present the eyes in an anterior position; and • Form the base for the facial muscles

18. Skull cont. • Most bones of the skull are joined by interlocking joints termed sutures • The mandible is attached to the rest of the skull by a freely movable joint • Other random bones- • Hyoid bone-”U” shaped; not attached between lower jaw & larynx • Ossicles -”ear bones”- mallus (hammer); incus (anvil); stapes(stirrup)

19. THE CRANIUMPORTION OF THE SKULL • Frontal bone: • Forms the forehead • Parietal bone: • Forms the sides and the major top portion of the cranium, ( top of your head) • Temporal bone: • Located above you ears • Occipital bone: • Located at the back of the cranium • Houses the foramen magnum (spinal cord starts here) • Ethmoid bone: • Located just inside the eye socket at the top portion of the nasal bone.

20. Facial Bones-thirteen bones fused together, and a movable mandible. • Superficial facial bones – provides areas for the attachment of muscles • Deeper facial bones – separates oral and nasal cavities & help to form the nasal septum • The vomer is not paired-divides the nasal cavity • Nasal bones-small bones that form the bridge of the nose • Lateral to the nasals are the maxillary bones. • Below the eye orbits are the zygomatic bones (cheek bones). • Lateral to the bridge of the nose are the small lacrimal bones • Lower jaw is the mandible

21. Vertebral Column • Consists of 24 single bones called vertebrae. • two fused bones- the sacrum and coccyx • connected extending from the skull to the pelvis • Forms the body’s major axial support • Surrounds and protects the spinal cord- allowing the spinal nerves to extend

22. Number of Vertebrae • The 24 single vertebrae are groups as follows: • Cervical Vertebrae • 7 bones • Forms a concave shape • Commonly termed “NECK” • Thoracic Vertebrae • 12 bones • Forms a convex shape • Connected to the ribs • Lumbar Vertebrae • 5 bones • Forms a concave shape • Supports the lower back

23. LETS NOT FORGET THE SACRUM AND COCCYX • Sacrum • 5 FUSED bones • Forms a convex shape • Coccyx • FUSED bones • Termed the tailbone. • It is attached to the sacrum by ligaments

24. Cervical Vertebrae • Seven bones • Referred to as C1-C7 • The first two cervical vertebrae termed • Atlas (C1) • Lacks a body • Allows you to nod “YES” • Axis (C2) • Acts as a pivot for the rotation of the atlas and skull • Allows you to rotate your head to indicate “NO”

25. Cervical C3-C7 • Distinguished from the thoracic and lumbar vertebrae by several features: • They are the smallest; • Lightest; and • Triangular • They have foramina (holes) to allow blood vessels to go through.

26. Thoracic Vertebrae • 12 bones • Referred to as T1-T12 • Have larger body • Spinous process are long with a sharp downward hook

27. Lumbar Vertebrae • Five bones • Termed L1-L5 • Have massive block like bodies and short thick hatchet-shaped spinous processes

28. Intervertebral Disk • Vertebrae are separated by pads termed “fibrocartilage’ • They cushion the vertebrae and absorb shocks • Aging causes the water content of the discs to decrease and become thinner and less compressible. • Herniated disc- common back injury.

29. Vertebral Column Abnormalities:

30. Thoracic Cage • AKA- “RIBCAGE” or “BONY THORAX” • Forms a protective cone-shaped enclosure around the organs of the thoracic cavity • Heart; lungs; and major arteries/veins • Composed of the following: • The sternum • Ribs • Thoracic vertebrae

31. Sternum • AKA-“BREASTBONE”-flat • Is a fusion of three bones: • Manubrium • Top • Looks like a knot of a tie • Connects to the clavicle (collarbone) • Body • Middle • Forms the bulk of the sternum • Xiphoid process • Pointed tip • Can easily break with a strike or during CPR and can penetrate the heart or liver • Is attached to the first seven pairs of ribs

32. Is concave, you can feel it TRY TO FIND YOURS! • The sternum has three important bony landmarks • Jugular notch • Located on the manubrium • Sternal angle • Is where the manubrium and body join • It starts at the second rib • (DO NOT WRITE)so doctors use this to count ribs before placing needles into the body or to listen to heart valve You can also feel this !!

33. Rib Cage

34. Individual Rib • 12 pairs of ribs • All the ribs connect to the thoracic vertebrae • TRUE RIBS • First 7 ribs • Attached directly to the sternum • FALSE RIBS • Next 5 ribs • Attach indirectly to the sternum or lack a sternal attachment via cartilage) • Ribs 8-10 connect via cartilage to sternum • FLOATING RIBS • Last two pair of ribs • no sternal attachment