Motor neurons make parts of the body move, while sensory neurons send signals from the senses to the brain.
Muscles can shorten themselves, but cannot lengthen themselves. Every time a muscle contracts, it must be pulled back to its original length by another muscle shortening itself in the other direction.
Muscles in the palm control delicate hand movements such as playing the piano or typing.
The combined strength of all the hairs on one human head can support the weight of about 100 people.
The composition of the lens of a human eye is 65 percent water and 35 percent protein.
The cortex is the outer surface of the human brain. It is only 0.16 inches (4 millimeters) thick.
Myology is the science or branch of anatomy dealing with muscles.
The country of Yemen has the world's highest fertility rate among women at 7.6, the world's lowest — Switzerland at 1.5.
Nationwide, there are about 15,000 people in comas.
The daughters of a mother who is colorblind and a father who has normal vision will have normal vision. The sons will be colorblind, however.
Natural blondes have more hairs on their heads than redheads or any shade of brunette. A blonde has about 120,000 strands of hair, while a redhead has about 30% less strands than the blonde at about 80,000. Brunettes are somewhere in between the two.
The defect of color vision characterized by the inability to see the color red is called protanopia.
Neanderthal man, the first human being in the true sense, had a brain capacity 100 cc larger than modern man's.
The diameter of capillaries, or tiny blood vessels, is around 0.008 millimeters.
Nerve impulses to and from the brain travel as fast as 170 miles per hour.
The digestive system breaks down food, turning it into chemicals for the body to use.
Nerve signals may travel through nerve or muscle fibers at speeds as high as 200 miles per hour.
The digestive tract (the tube that food passes through) in a person's body is about 30 feet long.
Neurons are the identical cells that make up nerve tissue. They send electrical signals.
The easiest sound for the human ear to hear, and those which carry best when pronounced, are, in order, "ah," "aw," "eh," and "oo."
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