Stages of Sleep
Tuesday, December 18th, 2007You’re lying awake in bed with eyes open, awake but relaxed. Your beta brain waves indicate wakefulness. Growing more tired, you shut your eyes. Your brain activity slows down to alpha waves. You’re more relaxed, yet still wakeful.
Stage 1:
After several minutes in the alpha stage, your breathing rate and brain waves begin to slow down. You’re now entering Stage 1 sleep, a transitional stage of light sleep. Your heart rate is lowered and your breathing becomes shallow and regular. As your muscles relax, you might experience a sensation of falling, causing you to awake momentarily.
Stage 2:
Your brain emits theta waves along with K-complex waves and sleep spindles — so named because they resemble spindles on a loom. Stage 2 sleep lasts 10-20 minutes; it marks the beginning of actual sleep. You’re completely disengaged from the environment, unaware of most outside stimulation.
Stage 3:
It’s now perhaps 20-30 minutes since you first closed your eyes. You begin to enter Stage 3 sleep, a combination of theta and delta (very low frequency, high-voltage) brain waves.
Stage 4:
Soon, the theta waves disappear altogether, and you’ve arrived at Stage 4, the deepest phase of sleep. If you’re awakened, you’ll feel mentally groggy for several minutes. You won’t be able to make much sense. In this delta sleep, your muscles are completely relaxed, your blood pressure drops, your pulse and respiration are slowed. This is as close to hibernation as you get. So sleep tight!
Stage 5:
After 30-40 minutes of delta sleep, you begin retracing your steps back through Stages 3 and 2. It’s now about 90 to 110 minutes since you fell asleep. At this point, something dramatic happens. Your sympathetic nervous system is more active now than it is during wakefulness or slow-wave sleep. Blood flow to the brain increases. Your pulse, respiration and blood pressure increase and become irregular. Your temperature rises. Your eyes begin to dart back and forth, as if scanning the environment. Theta waves mingle with alpha waves, indicating a state similar to wakefulness. But you are not awake. You have arrived at REM (rapid eye movement) sleep.
Tags: Sleep
