Bones & Skeletal Structure

Bones are a type of hard endoskeleton found in all vertebrates. Bones give bodies their structure and protect internal organs. The adult human body has 206 bones. Infants are born with 300 bones--some consist of hard connective tissue and others are made of cartilage. Over time, the cartilage hardens and turns to bone and some bones fuse together. This accounts for the larger number of bones in children than in adults. By the time you are about 25 the process of cartilage hardening and bones becoming permanent is complete.

What are bones made of? Bones are made up of three layers: The outermost layer is called the periosteum. It is a thin membrane that covers the bone and contains nerves and blood vessels that nourish the bone. Bones can grow and change and need oxygen and nutrients just like the rest of the body. The next layer is called compact bone. This is smooth and very hard. Under the compact bone are many layers of cancellous bone. Cancellous bone is spongy and not quite as hard as compact bone. In the middle of the bone is marrow, which is a jelly-like substance. Bone marrow produces blood cells.

Bones to know… Skull – the bony framework of the head, protecting the brain and providing the structure for the face. Clavicle – either of two slender bones, front part of a shoulder (collar bone). Sternum – a strong bone in center of the chest that holds some of your ribs in place. Spine – a series of bones called vertebrae that run down the middle of the back. It allows you to bend and twist, protects the spinal cord and holds the body upright. Ribs – are 12 pair of bones that attach to the vertebrae (back) and some connect to the sternum (front), creating a cage. This cage protects vital organs such as the heart, liver and lungs.

More bones to know… Humerus – the long bone in the arm of humans extending from the shoulder to the elbow. Ulna – the bone of the forearm on the pinky side that also forms the elbow. Radius – thumb side of the forearm. Pelvis – bowl shaped structure including the hip bones that supports the spine and protects various systems. Femur – a bone in the upper leg extending from the pelvis to the knee. It is the longest bone in the body. Tibia – the shin bone; the inner (big toe side) and larger bone of the leg below the knee. Fibula – the outer and thinner of the two bones extending from the knee to the ankle.

Things that make you go hmm… The hardest bone in your body is the jawbone or mandible. Your lower jawbone is the only bone in your head that you can move. The femur is the longest bone in your body and is responsible for 25% of your height. Each arm and leg have 30 bones apiece. And although you can't see it, the smallest bone in your whole body is in your head. The stirrup bone behind your eardrum is only.1 to.13 inches (2.5 to 3.3 millimeters) long!

Output Activity Label the 12 bones discussed in class on the skeleton man diagram. Glue or tape onto the output side of your notebook.