Bone contain calcium, phosphorus, sodium, and other minerals, as well as the protein collagen. Calcium make the bones hard and allows them to support your weight. Calcium is also required by other parts of the body and some is released into the bloodstream by the bones. The amount of calcium stored in the bones is directly affected by intake of certain vitamins and minerals that you eat especially vitamin D.

The blood cells flowing through our bodies are made by soft bone marrow stored in the bones. There are certain special cells called stem cells in bone marrow which helpin the production of body's red blood cells and platelets. Body's tissues obtain oxygen through red blood corpusceles and platelets clot the blood whenever a person has cut or wound.

Bones are made up of two types of material - compact bone and cancellous bone. the solid, hard, outside part of the bone is made by the compact bone. It has ivory look and is extremely strong. blood vessels and nerves run through the bones in holes and channels from the periosteum, the bone's membrane covering, to its inner parts. The compact bone contains Cancellous (pronounced: kan-suh-lus) bone, which looks like a sponge .It is made up of a mesh-like network of tiny pieces of bone called trabeculae (pronounced: truh-beh-kyoo-lee). Red marrow is filled in the spaces in the network. It is found mainly at the end of the bones. The mesh network also conatain yellow fat which is mostly fat.

Long, fibrous straps called ligaments (pronounced: lih-guh-mentz) fasten the bones to other bones. Our joints contain a rubbery substance called cartilage which helps in supporting bones and protect them them where they rub against each other. Muscles and joints help in functioning of bones. Joints are pulled by musceles. Muscles allow us to move . Body functions such as chewing food and moving the food through digestive system is also helped by muscles.

There are more than 650 muscles in the human body. The muscles alone make up half the person's weight. tough, cord-like tissues called tendons connect the bones to muscles. They allow the muscles to pull on bones. If you wiggle your fingers, you can see the tendons on the back of your hand move as they do their work.

Brain and nervous system control and coordinate the movement of muscles. The upper part of the spinal cord called the stem and the structures deep within the brain control the involuntary muscles. Few parts of the brain known as cerebral motor cortex and the cerebellum regulate the voluntary muscles.

the motor cortex sends an electrical signal through the spinal cord and peripheral nerves to the muscles, causing them to contract. the muscles on the left side of the body is controlled by the motor cortex on the right side of the brain. the motor cortex orders the The cerebellum (pronounced: ser-uh-beh-lum) to co- ordinate the muscle movements. Messages are sent by sensors in muscles and joints through peripheral nerves to tell the cerebellum and other parts of the brain where and how the arm or leg is moving and what position it's in. smooth, coordinated motion is acheived from this feedback. You arm is lifetd by the message sent from the brain to the muscles in your arm. When you run, the messages to the brain are more involved, because many muscles have to work in rhythm.

Body parts are moved by muscles by contracting and relaxing. Bones can be pulled by muscles but they can't be pushed back to the original position. So they work in pairs of flexors and extensors. a limb at a joint is bent by flexor contraction. the same joint. For example, the biceps muscle, in the front of the upper arm, is a flexor and the triceps, at the back of the upper arm, is an extensor the biceps contracts when the elbow is bent. Then the elbow is straightened by the contraction and relaxation of biceps.