Sleep: what happens at night?
Sleep comes in stages that repeat during the night. Learn what happens in each stage, how your body clock and sleep pressure work, and run an anonymous class sleep survey.
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There are two basic types of sleep: non-REM sleep, which has three stages, and REM sleep. During the night you go through stage 1, 2 and 3 and then REM, and this cycle repeats several times. The first REM sleep starts about 90 minutes after you fall asleep.[2][1]
In stage 1 your heartbeat and breathing slow and your muscles relax. In stage 2 your brain waves slow and your body temperature drops. Stage 3 is deep sleep: heartbeat and breathing are at their lowest, and your body grows and repairs tissue.[2]
In REM sleep (rapid eye movement) your brain is very active, your breathing is fast and irregular, your eyes dart back and forth and you dream. Your arm and leg muscles are temporarily paralysed, which stops you acting out your dreams.[2][1]
Why sleep? Sleep seems to act like housekeeping, clearing waste that builds up in the brain while you are awake. It also helps the brain build the connections needed for learning and memory.[1]
Two things control when you feel sleepy. Your body clock runs on a roughly 24-hour rhythm and uses light from your eyes to stay on time; when it gets dark your body releases melatonin. And a chemical called adenosine builds up while you are awake, making you sleepier: caffeine works by blocking it.[1]
Children aged 6 to 12 need 9 to 12 hours of sleep and teenagers aged 13 to 18 need 8 to 10 hours. In a 2015 survey in the USA, about 6 in 10 middle-school students did not get enough sleep on school nights. Too little sleep is linked to problems with attention and behaviour.[3][4]
Try it: Anonymous class sleep survey
You need
- Small identical paper slips
- A box or bag to collect them
- Squared paper or a whiteboard for a bar chart
Safety
Keep it anonymous and kind: nobody has to answer, and nobody should be teased about their answer. Families have different routines.
What to do
- Agree the question: 'About how many hours did you sleep last school night?' Everyone answers for the same night.
- Each person writes only a number of hours on a slip (no names) and folds it. Writing nothing is fine too.
- Collect the slips in the box and mix them.
- Sort the slips into groups: under 8 h, 8–9 h, 9–10 h, 10–11 h, 11 h or more.
- Draw a bar chart. How many slips are in the 9 to 12 hour range?
- Discuss: what makes this a fair survey? What could make the answers less accurate?
What happens, and why?
Asking everyone the same question about the same night, and keeping it anonymous so people can answer honestly, makes the survey fairer. Comparing with the recommended 9 to 12 hours for ages 6 to 12 shows how the class compares. People often guess their sleep time, so the answers are estimates, just like the big national surveys.[3][4]
Play: REM or non-REM?
Something happens during sleep. Does it belong to REM sleep or to non-REM sleep?
Your best score is kept only on this device. Nothing is sent anywhere.
Quiz
Other ages: Ages 6–7 · Ages 15–16