Vanessa Ryan, St Augustine's, Baxter

The Skull	The Sternum & Rib Cage	The vertebral column	The arm	The leg	The shoulder girdle	The pelvic girdle

The human skeleton is made up of 206 bones that form a rigid framework to which softer tissues and organs of the body attach. Vital organs are protected by the skeletal system. The brain is protected by the surrounding skull and the heart and lungs are encased by the sternum and rib cage. Bodily movement is carried out by the interaction of muscular and skeletal systems. Muscles are connected to bones by tendons and bones are connected to each other by ligaments. Where bones meet one another there is usually a joint.

As an example, the forearm moves as a result of contraction of the upper bicep muscles and the relaxation of the lower tricep muscles. This produces a bend in the elbow. The contraction of the triceps and the relaxation of the biceps produces the effect of straightening the arm. Blood cells are produced by the bone marrow located in some bones. An average of 2,600,000 red blood cells are produced every second by the bone marrow to replace worn out or destroyed cells by the liver. Bones serve as a storage are for minerals such as calcium and phosphorus. When an excess is present in the blood, buildup will occur within the bones but when the levels of calcium and phosphorus in the blood is low, they are withdrawn from the bones to replenish the body's supply.

The human skeleton is broken up into different parts: the axial skeleton dealing with support and protection of head, neck and trunk. The appendicular skeleton deals with bones that anchor to the axial skeleton: the arms, legs, pelvis and shoulder girdle. There are also many types of bone structures and composition within the body serving different purposes.

The skull: There are 8 cranial and 4 facial bones making up the skull. The various parts serve a set purpose. The joints between bones of the skull are immoveable and are called sutures. For young babies the very top of the forehead meet with 3 cranial plates called the fontanelles (or soft spot in babies). The jaw or mandibles works on a third degree lever system: this makes it very strong.

The sternum: The sternum is a flat, dagger shaped bone located in the middle of the chest. Along with the ribs, the sternum forms the rib cage that protects the heart, lungs and major blood vessels from damage. The ribs are connected to the sternum by costal cartilage. This cartilage can stretch when you breathe in and out.

The ribs: The ribs are made up of 24 bones working in pairs. There are "true" ribs which are connected to the sternum and around to the spine. There are "false" ribs that connect to the spine at the back but connect to ribs on the front. There are also "floating" ribs that connect to the spine at the back but to nothing in front. The ribs are used to protect the heart and lungs fron injuries and shock that might damage them. Ribs also protect parts of the stomach, spleen and kidneys. They also help you breathe. As you inhale, the muscles in between the ribs lift the rob cage up allowing the lungs to expand. When you exhale, the rib cage moves down again, squeezing the air out of your lungs.

The vertebral column (this includes your backbone and spine): This consists of 33 irregular bones called vertebrae which travel the full length of your spine ending with the coccyx or tailbone. The tailbone has 3-5 bones that are fused together. In between the vertebae are intervertebral discs made up of fibrous cartilage that act as shock absorbers and allow the back to move. As a person ages, these discs compress and shrink, resulting in a distinct loss of height (generally 0.5 to 2.0cm) between the ages of 50 and 55. The vertebral column allows humans to stand upright and maintain their balance. It also helps to support arms and head, while permitting freedom of movement. It also provides attachment for many muscles, the ribs and some organs. It protects the spinal cord which controls most bodily functions.

The arms: Pound for pound, bone is almost as strong as steel. The single upper arm bone is called the humerus. It fits into the scapula of the shoulder. It is joined at the elbow by the radius and ulna. The radius is on top if you face your palm to the ground. The radius is more responsible for wrist movement and yet the ulna is longer and stronger. The hand is made up of 27 bones in the wrist, palm and fingers. They are tightly bound by ligaments. The fingers are made up of 14 bones called phalanges. A single finger bone is called a phalanx.

The legs: The thigh is called the femur. The femur is the longest, largest and strongest bone in the body. The leg, technically, is only the part from the knee to the ankle. The leg is made up of the fibula on the side away from the body and the tibia on the side nearest the body. The tibia connects to the femur to form the knee joint and with the talus, a foot bone, to allow the ankle to flex and extend. The tibia is larger than the fibula because it bears most of the weight, while the fibula serves as an area for muscle attachment. The foot or pes, contains 26 bones of the ankle, instep, and 5 toes. The foot's 2 arches are formed by the structure and arrangement of the bones and are maintained by tendons and ligaments. The arches give when weight is placed on the foot and spring back when the weight is lifted off the foot. The arches may fall due to a weakening of the ligaments and tendons in the foot. The patela or kneecap is a large, triangular bone between the femur and the tibia. It is formed in response to the strain in the tendon that forms the knee. The patella protects the knee joint and strengthens the tendon that forms the knee.

The shoulder girdle (this includes the 2 clavicles and 2 scapulae): The clavicle are the collarbones. They are a slender S-shaped bone that connects the upper arm to the trunk of the body and holds the shoulder joint away from the body to allow greater freedom of movement. One end is connected to the sternum and the other to the scapula. The scapula is a large, triangular, flat bone on the back of the rib cage commonly known as the shoulder blades. It serves as an attachment for several muscles.

The pelvic girdle: It is comprised of 2 coxal bones. As an adult the pelvic girdle supports the weight of the body from the vertebral column. It also protects and supports the lower organs, including the bladder and the reproductive organs. In men and women the pelvic girdle are different.