Whether you’re taking an afternoon nap or settling in for the night, your different sleep phases all serve a purpose. Here’s your sleep cycle explained.
The phases of sleep progress in a cycle from phase 1 to REM (rapid eye movement) sleep, after which the cycle starts again.
Phase one is light sleep, when you’re still half awake. Your muscles relax, your pulse slows and your eyes move from corner to corner. This phase lasts just a few minutes. The slightest disturbance will wake you and you may experience a sensation of falling. That’s because your muscles have started to relax.
You spend almost half of your total sleep time in phase two, called true sleep. It lasts for almost 20 minutes at a time and your heartbeat, breathing and brain waves slow down.
This is the start of deep sleep. You’re now thoroughly relaxed. In this phase huge, slow brain waves called delta waves begin to occur. Your breathing and heartbeat decrease to their lowest possible levels.
Phase 4: deep sleep
The brain produces almost only delta waves and it’s very difficult to wake you. If you’re disturbed during deep sleep, you’ll struggle to adjust to being awake and will feel disoriented and groggy.
Deep sleep is the phase during which some children experience bedwetting, night terrors and sleepwalking. It’s also the phase when testosterone and growth hormones are secreted. In adults, growth hormones ensure cells, skin, bone tissue and muscles remain healthy – your proverbial beauty sleep. In babies and children, they facilitate growth and trigger puberty.
Phase 5: REM sleep
This is the last phase of the cycle. It starts about 70 to 90 minutes after you’ve fallen asleep. Adults spend about 20% of their total sleep time in this state while for babies it’s about 50%.
During REM sleep, your brain rhythms look similar to those when you’re awake. Your eyes jerk rapidly in various directions, breathing becomes more rapid, your blood pressure rises and your muscles become temporarily paralysed.
It’s difficult to wake you from REM sleep and, if it happened, you would be disoriented and your thoughts bizarre.
Dreams occur during REM sleep. Some biologists say dreams are the brain’s way of sorting and deleting unimportant information, so it doesn’t become overwhelming. REM sleep and dreams are also essential for memory. After REM sleep, the entire sleep cycle starts again.
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