The Basics of Human Bones and Muscles
ByThe skeleton acts as a framework to shape, support and move the body. The bones of the skull, rib-cage and pelvis protect vital organs and the movement of the ribs allows the lungs to expand and contract during breathing. Bone is an important factory for the production of red and white blood cells and platelets, and a storehouse for mineral salts.
Bone is one of the hardest tissues in the body. Its density and strength come from calcium, phosphate and carbonate -crystalline salts deposited in the cartilage of the soft bones during infancy and childhood. Healthy bones need an adequate supply of these salts in the diet, as well as the right level of acidity, the hormone calcitonin (from the thyroid gland) and vitamin D in the blood.
Special areas in bones act as hardening and growth centres Skul1 and in long bones these are at one or both ends. The process of calcification (hardening of the bones) continues until the age of twenty-five. Whatever the age of a child, bone tissue is never static, but constantly being remodelled by two groups of bone cells responsible for breakdown and renewal. Some bones, such as those in the skull, fuse together as a child grows.
Bones can be flat (as in the skull), irregular (in the face and pelvis), long (in the limbs) or short (in the fingers). On the outer surface of any bone is a membrane called the periosteum. Beneath this lies a harder layer and the innermost part is like a honeycomb. Many bones have a central canal containing bone marrow, blood vessels and tiny lymph channels.
The skeleton is made up of many bones jointed or fused together. Ligaments are bands or sheets of strong, relatively rigid, fibrous tissue that bind bones together and so strengthen joints and help prevent dislocation. Skeletal or ‘striped’ muscles are attached to bones either directly or by tendons and help give the body its contours. They are made of bundles of elastic fibres lying close together which are able to contract or shorten in length. This contraction and relaxation enables the bones to be moved. Muscles have an extremely good blood supply to give them enough energy and oxygen for the work they do, and also to dissipate some of the heat they produce.
Different joints allow various forms of movement or none at all. The elbow and knee joints are hinges; the hip and shoulder joints function like a ball and socket, with a wider range of movement; the neck joint is a pivot; and the joints of the skull bones allow a gliding motion over each other in a young baby, but no movement in an older child after they have fused. Many joints are separated by a thin layer of fluid which lubricates the surfaces of the bones as they move against each other.
When things go wrong
The skeleton can only do its job well if it is undamaged. Fractures are a relatively common result of accidents involving children. Sometimes a fracture is obvious, with pain, tenderness, swelling, loss of movement, bruising and deformity. At other times, a broken bone may go unnoticed for several days because there are so few symptoms. A bone can break right across or it can splinter. ‘Greenstick’ fractures (where the bone is bent and partly broken) are often seen in the limb bones. If the skin remains intact after a fracture, it is said to be a simple or closed fracture; if there is a wound it is called ‘open’. If a broken bone has damaged an internal organ, the fracture is known as ‘complicated’.
If a child can’t move a fractured limb, the bone is probably damaged enough to make movement extremely painful. Any attempt to move the bone by using the muscles attached to it alters the position of the broken ends and hurts the surrounding tissues.
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