4-4. PIEZOELECTRIC EFFECT
a. Each bone is built around an FCT framework on which the apatite crystals are
deposited in a regular order. Apatite is a mineral, a form of calcium phosphate.
(Another mineral found in bones is calcium carbonate.)
b. When compressed, the apatite crystals produce a local electric current. This
phenomenon is known as the piezoelectric effect.
c. Presumably, this piezoelectric effect is produced in the bones of the lower
limb during walking. We know that tissues respond to local electric current. When
walking casts are used, fractured lower members tend to heal much more rapidly than
when the patient is bedridden. Bones tend to lose mass when they are not subjected to
forces as great as ordinary.
4-5. BUILDING UP, TEARING DOWN, AND REBUILDING OF BONE TISSUE
a. The living cells of the bones are osteocytes. When these cells are building up
bone tissue, they are called osteoblasts. When they are tearing down bone tissue, they
are called osteoclasts.
b. This building up, tearing down, and rebuilding are continuous processes
throughout the life of the individual human being. The building and rebuilding respond
specifically to the directions of force applied to the body at that particular time.
Therefore, throughout the life of the individual, the skeleton can be remodeled and
changed continuously in reaction to applied forces.
Section III. DEFINITION AND TYPES OF BONES
Bones are those individual organs that are elements of the skeletal system.
The individual bones of the skeleton can be categorized into three major groups
according to their general shapes: