SKELETON SYSTEM
Your skeleton is a protective and supportive structure of bones. Skull bones protect the brain. Rib bones create a cage around your chest which protects your lungs and heart.
Muscles are attached to bones and pull on them to create movement. Blood is created in the center of bones. The inner part of a bone is filled with bone marrow. Bone marrow is soft.
Bone marrow creates red and white blood cells. Red blood cells carry oxygen throughout the body. White blood cells are a part of the immune system which protects the body from germs.
WHAT ARE BONES MADE OF?
There are two types of bone. One is called compact bone and the other is known as spongy bone. Compact bone is the firm and smooth part on the exterior of a bone.
The long bones in your arms and legs are mostly compact bones. Spongy bone is usually found under compact bone.
Spongy bone is also found at the ends of the arm and leg bones. The pelvis (hipbone), ribs, vertebrae, and skull also contain spongy bone.
Your skeleton also contains cartilage. Cartilage is similar to bone but softer and bends easily. There is cartilage in body parts that must be tough but able to bend. There is cartilage in the outer part of your ear and the tip of your nose.
JOINTS
Joints are where two or more bones meet and form a point where bones can flex back and forth. Most bones are tied together at joints by a tough material called ligaments.
