Guess what you'll spend one-third of your life doing. Sleeping! Believe it or not, if you live to be 75, the hours you sleep each night will add up to about 25 years of slumber.
It might seem like all that sleep is a giant waste of time. But scientists now know that while you're snoozing quietly in your bed, there's lots going on inside your brain and body.
Cycling through Sleep
For one thing, you sleep a cycle of five different types of sleep, over and over each night. When you first lie down and begin to fall asleep, your body enters what sleep experts call Stage 1 sleep. You're still very close to being awake, but your brain begins to work more slowly. Your body relaxes, and your closed eyes start to roll around. If someone woke you from this stage, you'd probably say that you weren't even asleep yet. After several minutes, you sink a little deeper, into Stage 2 sleep. You'd still be easy to wake up, but you'd probably know you'd been snoozing.
Then you really relax and fall deeply asleep, into Stage 3 sleep. Your heart slows down, and you breathe more slowly, too. Noises nearby would probably not wake you. Finally, you sink into the deepest sleep of all, called Stage 4. Once you're in Stage 4 sleep, you're very hard to wake up. And if someone does manage to wake you, you'll be very confused about where you are and what's happening.
The first time you reach Stage 4 sleep after going to bed, you stay there for almost 20 minutes. That's the longest chunk of deep sleep you'll have all night. After that, you slowly move back up through Stages 3 and 2.
And then your sleep gets really interesting.
Sweet Dreams
As you come back up through a period of Stage 2 sleep, you shift into Rapid Eye Movement, or REM, sleep. It's called REM sleep because when you're in it, your eyes-behind your closed eyelids-slide quickly back and forth, and back and forth, as though you were watching the ball in a tennis game. Your brain becomes much more active during this sleep stage, almost as active as when you're awake. Instead of resting, a brain in REM sleep is racing! And while your eyes are darting from side to side, a very detailed story is running through your head: you're dreaming.
It's during REM sleep that you dream your strangest dreams, the ones that sound so very mixed-up when you describe them the next morning. As you drift into a REM-sleep dream of singing toothbrushes or a dog that says he's your uncle, your body changes, too. Your breathing and heart rate sometimes speed up. Scientists say that your brain waves-measurements of the electrical activity in your brain-look almost the same during REM sleep as they do when you're awake. When you enter REM sleep, you go from being completely relaxed to being ready for action. And yet, you never move. That's because you can't. You're paralyzed!
When you're in REM sleep, your brain cuts off all the messages that might tell your body to move. You never pull up the covers or even roll over. Except for your shifting eyes, your breathing, and a twitch every now and then, you lie perfectly still as you dream. Scientists guess that may be to prevent you from acting out any wild scenes in your dream and hurting yourself.
Does Dreaming Make You Smarter?
You'll spend more than two hours each night in REM sleep, dreaming. Why do you dream? Scientists are still trying to figure that out.
One idea is that dreaming helps you organize your memories. It gives your brain a chance to sort through everything that happened during the day, storing what you need to remember and tossing out details that don't matter.
Experiments show that REM sleep definitely can help you learn better. In one test, volunteers were taught a new skill. That night, some of them were awakened whenever they entered REM sleep. The others were awakened the same number of times but only during non-REM sleep. The next day, the people who got their REM sleep tested better than the others at performing the new skill.
Researchers now think dreams may be like exercise for your brain, and dreaming may actually help your brain develop. Newborn babies spend almost half of their sleep time in REM sleep! But adults, whose brains aren't developing so much anymore, spend only about one-fifth of their sleep time dreaming.
Going without Sleep
During the day your muscles are busy stretching and pulling as you run, jump, or even just sit. Lying down asleep and fairly still gives those muscles a chance to repair and grow stronger. Scientists carried out an experiment on weight-lifters. For one night, they allowed the athletes to sleep only three hours. The next day, none of the athletes could lift as much weight as they had before. If you didn't sleep, you wouldn't be as strong either.
As you lie snoozing, you're busy healing and growing. Your body is releasing more of the chemicals that help it create new bits of skin, muscle, and other parts of you. Sleep is so important for healing that when you're injured or sick, your body releases chemicals to make you feel sleepier. Just recovering from a sunburn can make you sleep longer.
In one experiment, scientists kept a group of rats awake to study what would happen to them. After one week with no sleep, the rats began losing weight, even though they were eating more and more food. Their body temperatures dropped below normal, and cuts and scrapes wouldn't heal. After 16 sleepless days, the rats died. Why?
Most animals, including you and those rats, have an immune system-a kind of defense force that fights disease-causing germs. Special cells in your immune system work every day to destroy germs that manage to slip inside you. When you sleep, your immune system has a chance to create more of those special germ-fighting cells. If you don't sleep as much, it cant make as many.
When the scientists examined the sleep-deprived rats, they discovered that they had become infected by germs that their bodies could ordinarily fight off easily. But in the overtired rats, the infections had just grown worse and worse. Without sleep, the rats' immune systems couldn't do their job.
You've Got Rhythm
If you've ever been around newborn babies, you know that night and day don't mean much to them. They might be awake at three o'clock in the morning and asleep at four o'clock in the afternoon. It takes months for most babies to adjust to the rhythm of sleeping at night and being awake during the day.
But like most people, you probably feel wide awake in the morning, even if you went to bed late the night before. After lunch, you may begin to feel sleepy. In late afternoon, though, you perk up and feel wide awake again around supper. Then, just at bedtime, that sleepy feeling comes over you again. The regular pattern each day of wide-awake times and sleepy times is called your circadian rhythm.
Inside your brain, in the region where nerves carry the information from your eyes, are two tiny clusters of cells, each about the size of a pinhead. They're what scientists sometimes call your biological clock. These cells seem to keep track of the time. They let your body know when to produce chemicals to wake you up or make you sleepy. They keep your brain alert and ready to receive all the information your eyes, ears, and other parts of your body pass along. Then, as night comes, they work with different parts of your brain to stop making wake-up chemicals and start making sleep-time chemicals.
Almost every living thing follows its own special pattern of sleepiness and wakefulness in the 24 hours of each day. Bees do, for instance. They visit flowers to gather nectar only at a certain time of day. And many flowers open at the same hour every day, too.
Sleep on It
Though there are still many mysteries to be solved about what goes on inside you during sleep, scientists know for sure that you need to sleep to keep your body healthy and your brain active. Missing just two hours of sleep one night will make you less alert the next day. You won't do as well in your schoolwork or physical activities.
And if you miss a whole night's sleep? Then you're really in trouble. You'll start to feel worried and unhappy. It might be hard to find the right words when you talk. You'll have difficulty concentrating and remembering, and your body might not be able to fight off
Sleep is so important, your body makes sure it gets some. If you're tired enough, your body will make you fall asleep, even if you don't want to. Adults who don't get enough sleep often take tiny little naps of just a second or two called microsleeps. They don't mean to take these naps. Their bodies just take them the moment they're sitting still. In one experiment, researchers found that overtired people could fall asleep even when their eyes were held wide open with tape!
Scientists still can't explain why some people need more sleep than others, or why some animals get by with a lot less sleep than people can. But one thing's for sure: getting enough sleep will help scientists figure it out