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Human Body
movable elastic connection. At the back, the ribs are fitted on to the vertebrae by tiny gliding, rotating joints permitting the rib cage to adopt different rhythms of breathing. In contrast to these is the large ball and socket joint of the hip which holds the rounded end of the femur in a self-lubricating socket. The head rotates on the two top vertebrae in the neck enabling us to shake, nod and turn our heads. Bone Structure
Bone is like reinforced conerate. Its hardness is imparted by deposits of calcium carbonate and calcium phosphate in the matrix. Strength is imparted by reinforcing fibres. Living cells of the bone are nourished by blood vessels that permeate the bone. Cavities within bones house bonemarrow in which billions of red blood cells and millions of white one are produced everyday.
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By three months after coneption, a complete skeleton composed of cartilage is formed. Bones are formed later by ossification. Childrens' bones are more flexible and less brittle and, therefore, less susceptible to fracture. In old age-excessive reabsorption produce osteoporossis and bones become brittle and easily broken.
The Structure of Joints
Our body is in almost constant motion. Legs move in walking and running; hands and arms move in a bewildering variety of activities, jaws open and close; eyes dart back and forth.
We would be as immobile as statues if our skeleton were one continuous structure instead of being composed of more than 200 bones connected in joints. The space between the bones in a joint is filled with a lubricating fluid. It reduces the friction between the moving parts. The whole joint is prevented from moving too far by the liga-ments which connect the two bones at the joint, so preventing dislocation
Joints are commonly classified as : immovable, slightly movable and freely movable. The last group consists of ball and socket, pivot, and hinge joints. Shoulder joint is One of the most mobile while in the skull flat bony plates
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