By Barbara Terry
Your brain waves move fast when you are awake. This is known as "beta" waves. When you lie down, close your eyes and become drowsy your brain wave tend to start slowing down; this is known as the "alpha" state.
Five minutes into the alpha state your body slips into the Stage 1 sleep.
Stage 1 is the lightest sleep stage
During Stage one your body is very busy. Your muscles begin to relax, your heart rate and brain temperature rises, and your breathing begins to slow down. This stage occurs while your still awake. EEG waves begins to take over the brain wave activities. If you were awakened during this stage of sleep, you wouldnt feel like you were asleep. This stage lasts for only a few minutes.
Stage 2 is the K-Spindle sleep stage
Stage two is a light level of sleep in which a burst of electrical activity (spindles) intrude into your EEG. Your brain waves seem to slow down even more. Sleep walking and sleep talking normally occurs in this stage. You would feel like you were sleep if awakened now. This stage usually lasts about 15 to 30 minutes.
Stage 3 and 4 are the slow wave sleep stages (Deepest sleep)
Your brain waves slow down tremendously. These are called delta waves. This part of sleep is sometimes referred to as the slow wave sleep. This two stages last a total of 30 to 40 minutes on top of your first sleep cycle.
During Stage three your breathing becomes very slow and your heart rate slowly drops. Your brain generates stronger electrical impulses than the impulse it produces while you're awake. Stage three is the stage you are in when it takes a lot to wake you up. Most of your dreaming takes place in this stage. Your body can not move; it is temporarily paralyzed. This is why you sometimes feel that you cant run or scream in a nightmare, because the sleeping brain believes what it sees. This stage is where dreaming and REM sleep occurs.
Stage four is the deepest level of sleep, and your brain during this period will show large, slow EEG waves. Certain hormones and chemicals are released into the body, growth hormones is one of them. Teenagers need more stage four sleep than older people do. Once you get over the age 70, stage four sleep may disappear from your sleep cycle. This stage gets shorter and shorter as your rest cycle continues, and by the end of your cycle stage four may not exist any more. Once stage four has been reached, we descend back through stages 3, 2, and 1 before beginning REM sleep.
During a normal healthy nights sleep a person experiences four to five cycles of REM and non- REM sleep. Each sleep cycle lasts about 90 to 100 minutes.
* (EEG) Electroencephalogram measure of electrical brain activity.
For more information, please see the related weblinks on the Stages of Sleep Homepage.
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