Monthly Archives: April 2014
196.WHAT ARE OUR TEETH MADE OF?
Do you brush your teeth at least twice a day? If you do, and you brush hard, have you ever wondered why you don’t wear your teeth down? The fact is that our teeth are pretty tough—about as hard as rocks. Every tooth is made up of the same two parts: a root, or roots, to anchor it in the jaw bone, and a crown, the part that can be seen in the mouth.
195.WHAT ARE OUR BONES MADE OF?
The strength of normal, healthy human bones is amazing. The saying that our bones are “twice as strong as oak” is not far from wrong.
Bone needs to be strong because it forms the framework, or skeleton, that supports the whole body. Bones vary in shape and size according to the type of animal to which they belong. Fish and small birds have tiny bones. Elephants have bones that weigh several hundred pounds!
194.HOW DO OUR MUSCLES WORK?
In our bodies there are certain cells which make up connective tissue — tissue that joins the various parts of the body together. All the cells in connective tissue can contract, or tighten up. In some parts of the body, these cells can contract to a special degree, so they transform themselves into muscle.
At those points in the body where muscle cells are used frequently, they multiply and join together to form a single smooth muscle composed of many fibers.
