Axial Skeleton

Bones of the skull, thorax, and vertebral column

Form longitudinal axis of the body

Appendicular Skeleton

Bones, limbs, and girdles that attaches themselves to the axial skeleton

Functions of the skeletal system

- Support

- Storage of minerals

- Blood cell production

- Protection

- Leverage

Six categories of bones

(based on shapes)

- Flat bones

- Sutural bones

- Long bones

- Irregular bones

- Sesamoid bones

- Short bones

Flat bones

- Thin, roughly parallel surface

- Cranial, sternum

Sutural bones

- Irregular bones formed between the cranial

- Number, size, and shape vary

Long bones

- relatively long and slender

- various bones of the limbs

Irregular bones

- Complex shapes

- vertebrae, bones of pelvis, facial bones

Sesamoid bones

- Small, flat, and somewhat shaped like a sesame seed

- Develop in tendons, knees, and hands

 - Individual variation in location and number

Short bones

- Small and boxy

- bones of the wrists (carpals) and ankles (tarsals)

Skull Surface Features

- Canal or meatus (large passageway)

- Process (projection or bump)

- Sinus (chamber within bone, usually filled with air)

- Foramen (small rounded passageway)

- Fissure (elongated cleft or gap)

Humerus surface features

- Head (expanded proximal end that forms part of joint)

- Tubercle (small, rounded projection)

- Sulcus (deep, narrow grove)

- Tuberosity (small, rough projection; may occupy broad area)

- Diaphysis (shaft; elongated body)

- Trochlea (smooth, grooved articular process)

- Condyle (smooth, rounded articular process)

Femur surface features

- Trochanter (large, rough projection)

- Head 

- Neck (narrow connection between head and diaphysis)

- Diaphysis

- Facet (small, flat articular surface)

- Condyle

Pelvis surface features

- Crest (prominent ridge)

- Fossa (shallow depression or recess)

- Line (low ridge; more delicate than crest)

- Spine (pointed or narrow process)

- Ramus (extension that make angles with rest of structure)

Four bone cells types

- Osteocytes

- Osteoblasts

- Osteoprogenitor cells

- Osteoclasts

Osteocytes

- Mature bone cells that cannot divide

- Most numerous bone cell type

- Maintain protein and minerals content

- Occupy lacunae (pocket)

Osteoblasts

- Produce new bony matrix

- release of proteins and other organic components to produced unmineralized matrix (Osteoid)

- deposit calcium salt to transform osteoid into bones

Osteoprogenitor cells

- Mesenchymal (stem) cells that produce cells that differentiate into osteoblasts

- Important in fracture repair

- Located:

~inner lining of periosteum

~lining endosteum in medullary cavity

- lining passageways containing blood cells

Osteoclasts

- Remove and remodel bone matrix

- Giant cells with 50+ nuclei

- Release acid and proteolytic enzymes to dissolve matrix and released stored minerals

Osteolysis

loosening

Compact bones

- Functional unit is osteon

- Canaliculi connect lacunae with each other and central canal

- Strong along its length

Spongy bone

- Located where bones not heavily stressed or in many directions 

- Lamellae form struts and plates (trabeculae) creating an open network

- Reduces weight of skeleton

- No blood vessels in matrix

Periosteum

- Two layers:

~Fibrous outer layer

~Cellular Inner Layer

Functions:

~Isolate bones from surrounding tissues

~Route for blood and nervous supply

~Actively participate in bone growth and repair