BIOLOGY: Skeletal System

Skeletal System

Vertebrae

1.    Cervical – 7

2.    Thoracic – 12

3.    Lumbar – 5

4.    Sacral – 1

5.    Coccygeal – 1

A typical vertebra consists of:

1.    Centrum – carries most of our body weight

2.    Atlas – used to nod our head

3.    Axis – used to move head side by side

4.    Ribcage – bony basket formed by sternum & thoracic vertebrae

5.    Dorsal Ring of Bone – neural arch which surrounds & protects spinal cord

Ribs – each pair of ribs is attached dorsally to a separate vertebrae

1.    7 attached ventrally to sternum

2.    3 attached indirectly by cartilage

3.    2 are floating (no attachment)

Classification of Bones

1.    Long bones
- strong, hollow, light
- support weight & used for movement
- femur, humerus, tibia, fibula, ulna, radius

2.    Short bones
- support weight & allow many small movements
- carpal, tarsal, phalanges

3.    Flat bones
- found whenever there is a need for protection of soft body parts
- skull, pelvis, ribs, hyoid, shoulder blade

4.    Irregular bones
- peculiar
- vertebrae, ear bones, ossicles

5.    Sesamoid
- small & rounded
- enclosed in tendons
- facial bones

Joints
- junction sites of 2 or more bones
- facilitates flexibility & movement

1.    Immovable
- joint firmly united but doesn’t move
- sutures

2.    Slightly movable
- allows slight movement
- vertebrae

3.    Movable
- allows angular or rotary movement
- has a connective tissue w/c secretes synovial fluid w/c lessens friction & absorbs shock
- further classified into:
      a. ball & socket
           - allows movement in all directions
           - shoulder & upper arm, femur & pelvic
      b. hinge
           - allows bones to move forward/backward
           - arm & elbow, femur & lower leg
      c. pivot
           - allows 2 kinds of movement, side – side, up & down
           - neck
      d. gliding
           - allows bones to slide along each other
           - backbone, carpals, tarsals

Structure of a long bone

Periosteum
- a tough sheet of fibrous connective tissue
- outermost part of bone
- Functions:
  a. protective sheet
  b. support to tendons that attach muscles to bones
  c. ability to form new bone tissue

2 Types of Tissues

1.    Compact bone
- layers of bone tissue beneath periosteum
- hard but not fibrous
- gives bone resiliency
- strength due to calcium phosphate

2.    Spongy bone
- encased w/in compact bone
- softer & lighter in weight
- contains red bone marrow

Bone Marrow

1.    Red BM
- consists of fat producing cells
- can be found in flat bones

2.    Yellow BM
- composed chiefly of tissue
- no blood-producing functions

Bone Remodeling Cells

1.    Osteoblasts
- bone building cells
- secrete protein collagen

2.    Osteoclast
- large multinucleated cells
- bone breakdown