Main Components:

*See the first picture.

• Axial Skeleton (blue) - head, neck, back, chest

• Appendicular Skeleton (green) - This includes everything else and appends (attaches) to the axial skeleton. Together, the whole skeleton with 206 bones for the average adult is formed. The second picture shows a skeleton labeled with what can be considered the main parts.

Functions:

• Support - gives the body its shape

• Protection - helps protect organs

• Movement

• Produces Blood Cells

• Stores and releases minerals and fat

Classification of Bones:

• *Long and slim (ex: femur) *Long Bones can be found in the limbs!

• Short and wide (ex: cuneiforms in the foot)

• *Flat (ex: frontal bone) *Flat Bones are often on the outside of organs!

• Irregular (ex: the vertebra)

• Sesamoid (ex: the patella)

**There are also sutural bones; these types of bones are in between sutures in the skull. See #4 below for more information on sutures and sutural bones.

Main Parts of the Bone:

1. Proximal epiphysis - This is the "top" end of a long bone. It helps forms a joint and has red bone marrow which produces blood cells.

2. Distal epiphysis - This is the "bottom" end of a long bone. It also helps forms a joint and has red bone marrow which produces blood cells.

3. Diaphysis - The diaphysis is the main part of the bone (see picture).

4. Metaphysis - Between the diaphysis and epiphysis is the metaphysis. It serves as a transitional zone.

5. Articular cartilage - This is a type cartilage that covers the ends of bones where the bones form joints; this helps to lessen friction between bones.

6. Compact bone - Compact bone is bone which is tightly packed together; being compact allows it to help provide strength and protection.

7. Spongy (aka cancellous) bone - Spongy bone helps level out the heavy, dense compact bone; thus, it becomes easier on the muscles to move the bones. Spongy bone can contain red bone marrow, which allows for blood cell formation.

8. Medullary cavity - The medullary cavity is a hollow area which contains yellow or red bone marrow.

9. Yellow bone marrow - Yellow bone marrow stores adipose tissue (fat) and has stem cells (the basic type of cell from which other specialized cells are formed) which will develop into cartilage, fat, or bone cells.

10. Red Bone Marrow - Red bone marrow are where red and white blood cells are created; platelets are created here too.

11. Endosteum - This is a thin tissue that lines the inner cavity of long bones.

12. Periosteum - The periosteum is a durable membrane which surrounds bones (except at the joints), has blood vessels, and helps supply bone with blood (which can also help to repair and/or regrow the bone if it is injured).

Joints:

• Fixed joints - These are called sutures; they are immovable and do not have a joint capsule.

Ex: The coronal suture in the skull. See the first picture.

• Slightly movable joints - Slightly movable joints have cartilage and are movable; however, like fixed joints, they do not contain a joint capsule

Ex: The nose.

• Freely Movable Joints - Free movable joints are also called synovial joints; these joints offer the highest level of movement and contain joint cavities.

Types of Freely Movable Joints and Examples:

Gliding Synovial Joint - In between the tarsal bones (near the ankle).

Condyloid Synovial Joint - The joint between the radius and carpal bones of the wrist.

Saddle Synovial Joint - The joint in between trapezium carpal bone and first metacarpal bone in the thumb.

Ball and Socket Synovial Joint - The shoulder joint.

Hinge Synovial Joint - The elbow joint.

Pivot Synovial Joint - The joint between the first and second vertebrae in the neck.