What sleep does for you
- Sleep is a natural, reversible state of rest that your brain and body drop into each night.
- Sleep supports your thinking, because the brain sorts and strengthens the day's memories overnight.
- Sleep supports your body, because most physical repair and growth happens once you are deeply asleep.
- Sleep supports your mood, because a full night leaves you calmer and slower to snap at people.
The four sleep stages
- Stage 1
- You are drifting off, your muscles loosen and the smallest noise can pull you straight back to being awake.
- Stage 2
- You are properly asleep but still lightly so, and your heart rate and breathing slow down.
- Stage 3
- Deep sleep begins, brain activity settles into large slow waves and you become much harder to wake.
- Stage 4
- This is the deepest sleep of all, where your body does most of its repair work and waking you takes real effort.
- Stages 1 and 2 together are called light sleep, and stages 3 and 4 together are called deep sleep.
REM sleep
Definition
REM sleep
Rapid eye movement sleep: a stage in which the eyes dart about and the brain is highly active, when most dreaming happens, while the body's muscles stay relaxed and still.
- REM stands for rapid eye movement, and it is named after the way the eyes flick about behind closed lids.
- Your brain is highly active in REM, close to how active it is when you are awake.
- Your muscles meanwhile stay limp and still, so you do not act out what you are experiencing.
- Most dreaming happens in REM, which is why being woken during it so often catches you mid-dream.
- Everything that is not REM, meaning stages 1 to 4, is grouped together as non-REM sleep.
Common Mistake
- Do not write that the brain shuts down during sleep, because in REM it is almost as busy as when you are awake.
- Do not say you dream evenly all night, because dreaming clusters in the REM part of each cycle.
- Do not treat REM as a fifth deep stage, because it is a different kind of sleep rather than a deeper one.
The sleep cycle
Definition
Sleep cycle
A repeating pattern of sleep stages, lasting about 90 minutes, that you move through several times a night, ending each time with a burst of REM sleep.
- You do not pass through the stages once and stop, you loop through them again and again.
- One loop takes you down from stage 1 into deep sleep, back up through the lighter stages, and then into REM.
- A full loop lasts roughly 90 minutes, so an ordinary night holds several of them.
- The balance inside the loop shifts as the night goes on, with deep sleep filling the early cycles and REM taking up more of the later ones.
- That shift is why a short night costs you REM in particular, since the REM-heavy cycles are the ones your alarm cuts off.
Example
- You get to bed at midnight and your alarm goes at half six.
- The deep sleep came early, so your body still got its repair time.
- What you lost was the last cycle or two, and those are the REM-heavy ones, which is why you wake foggy rather than aching.
Turning this into marks
- Name the four stages in order and say what changes as you go deeper.
- For REM, pair the active brain with the still body and with dreaming.
- The mark most often lost is listing the stages without attaching what sleep achieves.
Self review
- Name the four sleep stages in order.
- What is your body doing during stages 3 and 4?
- What does REM stand for, and what is your brain doing in it?
- About how long does one full sleep cycle last?
- Why does cutting an hour off the end of your night cost you mostly REM?
