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Human neurons are so small that they require a microscope in order to be seen. However, some neurons can be up to 3 feet long, such as those that extend from the spinal cord to the toes.
The familiar sounds of your heart are made by the heart's valves as they open and close.
Adult head lice are gray, about ? inch long, and often have a tiny dot on their backs. A female can lay between 50 and 150 eggs within the several weeks that she is alive. They feed on human blood.
According to the Migraine Research Foundation, migraines are the third most prevalent illness in the world. Women are most affected (18%), followed by children of both sexes (10%), and men (6%).
The U.S. Preventive Services Task Force recommends that all women age 65 years of age or older should be screened with bone densitometry.