The sleep cycle
- Light sleepDrifting off; easy to wake
- Deeper light sleepHeart rate and temperature drop
- Deep sleepBody repairs; hard to wake
- REM sleepVivid dreams; muscles go limp
About 90 minutes
Each cycle takes roughly 90 minutes, repeating 4 to 6 times a night.
What sleep does
Files memories
Moves the day's learning into long-term storage
Takes out the trash
Fluid flushes waste from the brain at night
Repairs the body
Growth hormone peaks in deep sleep
Boosts immunity
Short sleepers catch more colds
How much is enough
| Age | Recommended sleep per night |
|---|---|
| Teenagers (13-18) | 8 to 10 hours |
| Adults (18-60) | 7 or more hours |
| Adults 65 and older | 7 to 8 hours |
Staying awake 17 to 19 hours can slow reactions about as much as a 0.05% blood alcohol level.
Remember
Sleep isn't wasted time. It's when your brain does its housekeeping.
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Answer key
- How long is one sleep cycle?About 90 minutesIt repeats 4 to 6 times a night.
- When do most vivid dreams happen?REM sleepDuring REM, muscles go limp so we don't act out dreams.
- How much sleep do most adults need?7 or more hoursSeven or more hours a night.
- What does the brain do at night?Files memories and flushes out wasteSleep is busy housekeeping time.
- Staying awake 17-19 hours can slow you about like:A 0.05% blood alcohol levelDrowsy driving is dangerous.