Dogs sleep, cats sleep, and you sleep. All mammals and birds sleep. Scientists are not sure if fish, reptiles, and insects sleep.
Big animals sleep less, and small animals sleep more. Elephants and giraffes sleep only 2 to 4 hours a day. Bats, opossums, and armadillos sleep 18 hours a day or more!
Even kids need more sleep than grownups. A newborn baby sleeps 17 to 18 hours a day. A 10-year-old needs about 10 hours of sleep a night. Grownups need between six and nine hours of sleep a night. Some people need more sleep than others.
WHY DO WE HAVE TO SLEEP?
Scientists do not know for sure why you sleep. They do have some ideas.
Safety could be one reason for sleep. People and other animals might sleep because it keeps them safe at night. It’s hard to see in the dark. Enemies could sneak up and attack animals that are wandering in the darkness. Most mammals and birds go to trees, underground dens, or nests at night. Prehistoric people went into caves or other shelters. They covered up with furs and fell asleep. You go into your home at night and snuggle up in bed.
Sleep might also help your body work better. Things go wrong if you do not get enough sleep. It is hard to think and work and play unless you get plenty of sleep.
WHAT HAPPENS WHEN WE FALL ASLEEP?
Scientists have learned a lot about what happens when you lie down, close your eyes, and fall asleep. They study people in sleep labs.
Sometimes your eyeballs move back and forth while you’re asleep. They move fast. Scientists call this kind of sleep REM sleep. REM stands for rapid eye movement. Your body may twitch during REM sleep. Your brain is also very busy during REM sleep. It is almost as busy as when you are awake. What do you think your brain is doing? Here’s a clue: You dream during REM sleep.
There is another kind of sleep. Your eyeballs do not move. Scientists call this NREM sleep. NREM stands for nonrapid eye movement. Your brain is not very busy during NREM sleep. You go back and forth between REM and NREM sleep all night long.
WHY DO WE DREAM?
Scientists have done many studies on dreams. They think your senses may have a lot to do with dreams. In dreams, you see and hear things. Dreaming is not like thinking about things.
You have feelings during dreams. You may feel happy or angry. You feel fear if you have a nightmare.
Your memories may have something to do with your dreams. Dreams are often like stories that stop before they are finished.
DO DREAMS MEAN ANYTHING?
People in ancient times looked for meaning in dreams. The ancient Egyptians believed dreams could tell the future. Some psychologists think that dreams show what people feel deep inside. They ask people to talk about their dreams.
Some scientists think that dreams have no meaning. They think that dreams just come from nerve signals in your brain. Other scientists think that dreams are important for memory. They may help your brain sort out what to remember and what to forget.
My source: Encarta ® 2007
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