Understanding the Human Skeletal System: Structure, Functions, and Divisions

1. The Skeletal System AP Biology

2. Divisions of the Skeletal System • Subdivided into two divisions: • Axial Skeleton – bones that form the longitudinal axis of the body • Appendicular Skeleton – bones of the limbs and girdles • Skeletal system also includes joints, cartilages, and ligaments • The joints give the body flexibility and allow for movement.

3. Functions of Bones • Support • Internal framework, support and anchor soft organs • Bones of legs act as pillars to support body trunk • Rib cage supports the throacic wall • Protection • Bones protect soft body organs • Ex. The skull protects the brain • Ex. The vertebrae surround the spinal cord.

4. Functions of Bones • Movement • Skeletal muscles use the bones as levers to move the body. • Remember – skeletal muscles are attached to the bones by tendons. • Storage • Fat is stored in internal cavities of bones. • Bones store minerals, most importantly • Calcium – important to muscles, nerves, and blood • Phosphorous

5. Functions of Bones • Blood Cell Formation • Hematopoiesis = blood cell formation • Occurs within the marrow of certain bones

6. Classification of Bones • The adult skeleton is composed of 206 bones. • 2 types of bone tissue: • Compact bone – dense and looks smooth • Spongy bone – composed of needlelike pieces of bone and lots of open space

7. Classification of Bones • Bones are classified according to shape into 4 groups: long, short, flat, irregular • Long: longer than they are wide, mostly compact bone • Short: cube-shaped, mostly spongy bone • Flat: thin, flattened, and usually curved, 2 thin layers of compact bone and a layer of spongy bone in middle • most bones of the skull, ribs, and sternum • Irregular: the vertebrae and the hip bones

8. Structure of a Long Bone • The diaphysis makes up most of the bone’s length, composed of compact bone. • Covered by a protective connective tissue membrane called the periosteum • The epiphyses are the ends of the long bone. • Mostly spongy bone • Cartilage covers this part of the bone. • Provides a smooth, slippery surface that lubricates the joints.

9. Structure of Bone • Epiphyseal line – thin line of bony tissue on epiphysis • Remnant of the epiphyseal plate • Causes the lengthwise growth of a long bone. • By the end of puberty, bones stop growing and epiphyseal plates are completely replaced by bone. • Mark the previous location of epiphyseal plate • Interactive Web

10. Structure of Bone • In adults, the cavity in the shaft of the bone stores adipose tissue (fat). • Yellow Marrow • In infants, this area forms blood cells, and red marrow is found there. • In adults, red marrow is only found in the cavities of spongy bone of flat bones and some long bones.

11. Bone Markings • Bumps, ridges, and holes in bones. • Indicate where muscles, tendons, and ligaments attach, and where blood vessels and nerves passed. • p.115

12. Axial Skeleton head, neck, trunk • SKULL • HYOID BONE (upper neck, under jaw, mandible) • VERTEBRAL COLUMN (spine/backbone) • THORACIC CAGE (rib cage-12 pairs) • STERNUM

13. Appendicular Skeleton limbs and bones connecting the limbs to the: • PECTORAL GIRDLE (scapula & clavicle) • UPPER LIMBS (arms) • PELVIC GIRDLE (coxal bones) • LOWER LIMBS (legs)

14. Bones of the Skull • 1. Frontal - anterior portion above eyes • 2. Parietal – one on each side of the skull, just behind frontal bone • 3. Occipital – forms the back of the skull and base of the cranium • 4. Temporal – forms parts of the sides and base of cranium • 5. Sphenoid – wedged between several other bones in anterior portion of the cranium • 6. Maxilla – forms upper jaws • 7. Mandible – lower jaws, only moveable bone of the skull

16. Vertebral Column • 3 types of vertebrae: • Cervical: First 7 (neck) • Thoracic: 12 vertebrae • Lumbar: Last 5 (lower back) • Intervertebral disks: flexible cartilage, cushion vertebrae and absorb shock • Sacrum: fusion of 5 vertebrae • Coccyx: fusion of 3-5 small, irregularly shaped vertebrae. • “tailbone”

17. Bones • Ribs – Thoracic Cage, 12 pairs • True Ribs – first seven pairs, attach directly to STERNUM by costal cartilage • False Ribs – last five pairs • Floating ribs – last two pairs • Pectoral Girdle: Shoulder. • Two clavicles (collar bones) and two scapula (shoulder blade)

18. Bones • Arms: Upper arm – humerus. Lower arm – radius and ulna. • Wrist – 8 small bones called carpels • Fingers – Metacarpels, Phalanges • Pelvic Girdle: Hips. Two large bones called COXAL BONES • Legs: Upper leg (thigh) - FEMUR. Lower leg – tibia & fibula. • Ankle and Upper foot – 7 bones called TARSALS, • Largest is the heel bone called the CALCANEOUS • Toes – Metatarsals, Phalanges

19. Broken Bones • A simple fracture is when the bone is broken cleanly but does not penetrate the skin. • A compound/open fracture is when the bone is sticking through the skin. • A greenstick fracture is when the bone cracks on one side only, not all the way through. • A comminuted (say: kah-muh-noot-ed) fracture is when the bone is broken into many fragments or crushed. • A compression fracture is when the bone is crushed. • A depressed fracture is when the bone is broken and pressed inward (typical of skull fracture). • A spiral fracture is when a break occurs from excessive twisting forces applied to the bone.