10 Little-Known Body Facts

Surprising statistics on stomach size, ear hair and more.

1.You Use 100-Percent of Your Brain
Think you're only using 10 percent of your possible brain power? Think again. A little critical thinking will have you calling shenanigans on that myth. After all, if you removed 90 percent of your brain, you'd basically be left with the thinking power of a sheep, according to Eric Chudler, Ph.D., research associate professor in the department of bioengineering at the University of Washington. Dr. Chudler has attempted to trace the history of the "10 percent myth" and written several articles on the topic. He reports that, during a functional magnetic resonance imaging (fMRI) scan, doctors can see what areas of the brain are being used, based on how much blood is being directed there. According to Dr. Chudler, 100 percent of the brain has been shown to have a function.

2.The average infant spends 18 hours a day sleeping.
If you have your own little one, though, you may have noticed that the sleep isn't consecutive (or, necessarily at times convenient to you). That's because babies sleep differently than adults. For the first few years of life, humans sleep a lot, but in shorter chunks, spending less time in REM sleep—the stage of sleep where the brain is active and dreams happen—and much more time in more relaxed slow wave sleep, according to the Society for Neuroscience. Adults pretty much sleep the opposite way: in long stretches, less time total, more REM. There's some evidence that the difference may be related to the needs of a growing body. Research has suggested that slow-wave sleep is connected to the release of human growth hormone.

3.Most people hit their peak bone mass at age 30.
Peak bone mass is the point where your body stops building up bone tissue. At that point, your bones won't ever increase in density. Men may be able to coast, but women lose a lot of their bone tissue during menopause and, according to the National Institute for Arthritis and Musculoskeletal and Skin Diseases, the lower your peak bone mass, the more likely you are to develop osteoporosis later. Unfortunately, as much as 75 percent of bone mass is related to genetic factors you can't control. But women can take charge of the other 25 percent by making sure they get enough calcium and vitamin D (particularly in their teens); taking hormonal birth control (which the NIAMSD says is linked to high bone density); not smoking; and exercising regularly—but not too much. Young women who exercise or starve themselves to the point they stop having their period also lose large amounts of bone tissue, and may never be able to build it back.

4.The average person's body holds 1.3 gallons of blood.
There's more than a milk jug full of fluid coursing through your veins, where it functions somewhat like a courier service. Blood is responsible for both delivering the things your body desperately needs—like oxygen—and carting off the things it desperately needs to throw out, like the toxic wastes that end up being filtered out of the body by the kidneys. And it does all of this very, very fast. The heart, the organ responsible for getting all that blood to move around, pumps as much blood as is in the body every minute; when you're sitting still, that is. Up your activity level and your heart can end up pumping more than five gallons of blood per minute.

5.You have 2 million tiny hairs in your inner ear.
Unlike hair growing on the surface of your ears, the presence of hairs, or "stereocilia," deep inside your head aren't considered a hygiene lapse. Instead, they're a vitally important part of your ability to hear, responsible for changing physical sound waves into electrical signals that can be understood by your brain, according to the British Hearing Research Trust. When stereocilia are hit with a sound vibration, they produce electricity and begin to "dance," stretching and compressing. In May 2008, researchers at St. Jude's Children's Research Hospital in Memphis figured out that this dancing, and the protein that causes it, is probably how stereocilia amplify sounds. If those tiny hairs can't dance, the brain they're connected to can't hear high-frequency sounds and might even be rendered deaf.

6.The eye has three separate processing systems.
New research shows it takes a village to help you see, according to the Society for Neuroscience. Right now, we know of at least three separate processing systems that help your brain make sense of visual data: One that focuses on shape, another devoted to color, and a third that takes on the task of interpreting movement and location. The Society reports that psychologists have found that humans can see and understand things like depth perception and texture even without color being involved. Instead, contrasts in light intensity help us pick up on this information.

7.Your tongue can pick up 5 different types of taste sensations.
Back in grade school, you probably learned that the human tongue can pick up four different kinds of tastes: sweet, sour, salty and bitter. But those textbooks left out another flavor sensation: umami. Taken from the Japanese word for "yummy," umami was first identified as a primary flavor back in 1908 by a Japanese chemist who was inspired to look for it after eating a bowl of seaweed soup. He found a chemical that is to umami what sugar is to sweet. It's monosodium glutamate, or MSG. But MSG isn't the only way to tickle your umami taste buds. Often described as the "savory" taste, umami sensations are naturally produced by foods like meat, aged cheese, tomatoes and mushrooms.

8.In 1900, the average life expectancy in the U.S. was 47 years.
Back then, only 4 percent of the population was older than 65 and, according to the Society for Neuroscience, most of them weren't doing so hot. Today, the average life expectancy is more than 77 years. So why are we living, and staying healthier, longer? There are a number of reasons, most of them related to health care. Since 1900, vaccinations have increased; we've improved safety standards for everything from workplaces to transportation; and we've developed medical breakthroughs that are making once life-threatening injuries, chronic ailments and illnesses curable, or at least controllable. But, according to the CDC, the biggest change has been in infant mortality. It's no coincidence that, as life expectancy rates have increased, mortality rates for babies have fallen by 90 percent, while rates of maternal deaths have dropped by 99 percent.

9.8-month-old babies have 1,000 trillion brain synapses.
Synapses are connections between neurons, the cells that control brain functioning. Baby brains go crazy with these connections, making many more than adult brains need. This way, the brain is able to learn what the most useful and efficient connections are, rather than having to have this information programmed into genes. If a synapse doesn't get used, it gets pruned away. By the time a child is 10, the number of synapses in his brain has been cut by half.
Because of this, what people learn in early childhood is incredibly important. If a child doesn't learn to talk, which has happened in some cases of severe neglect, it's likely they'll never be able to, because the synapses that would have enabled communication were never used and therefore destroyed. On the other hand, if the pruning process doesn't stop naturally, as it normally does, even essential connections can get the ax. Researchers at Stanford University recently discovered that certain degenerative diseases, including glaucoma, get their start when the brain continues to destroy synapses.

10.The volume of an average adult's empty stomach is 1/5 of a cup.
But that's empty. Stuffed with grub, the volume of the stomach can reach upwards of a little over a gallon. Of course, everybody's stomach size is different, and that, combined with recent developments in gastric bypass surgery, has left some people thinking that skinny-minnies just have naturally smaller stomachs. But that's not necessarily so. A study published in 2005 in the journal Obesity Surgery compared the stomach sizes of morbidly obese patients with those of controls and found that the obese don't have bigger stomachs. The stomach volumes were largely the same between patients and controls. However, other research has shown that people who have a history of overeating also have a larger-than-average stomach capacity. The take-away lesson: Having a naturally larger stomach volume alone won't make you fat, but regular overeating can increase your stomach volume and create a cycle where it becomes harder to get full and increasingly difficult to return to healthy eating habits, which can take a toll on your weight.