A night of sleep

About this video

It is late, there is a test tomorrow, and sleeping less looks like more time to study. But sleep is not one long, flat state, and it is not time switched off. Through the night you go round a cycle of different kinds of sleep, several times. In light sleep your heartbeat and breathing slow down and your muscles relax. In deep sleep your brain waves are at their slowest and it is hard to wake you; it is the sleep you need to feel refreshed, and most of it comes in the first half of the night. Then comes REM sleep, short for rapid eye movement: your eyes move quickly behind closed eyelids and most dreams happen. The first REM sleep comes about 90 minutes after you fall asleep, and REM periods get longer towards morning. Your brain stays busy all night: in REM sleep its activity comes close to how it looks when you are awake.

Sleep helps you learn and form long-term memories. People who don't sleep enough may get more colds and other infections, and in children and teenagers sleep supports growth and development. For adults, regularly sleeping less than 7 hours a night is linked to more mistakes and accidents and to several illnesses.

Tired people react more slowly. On lab tests of reaction and attention, being awake for 17 hours was similar to having some alcohol in the blood, and being awake for 24 hours was like being drunk. A long day of school and homework can easily reach 17 hours. So count sleep as part of studying, and don't drive, ride a motorbike or use dangerous tools after a night without sleep. And yet scientists are honest: everyone needs sleep, but its full purpose remains a mystery. This video goes with the lesson Why We Sleep in Knaph's Health Level 1 course.

Transcript

1. 0:00There's a test tomorrow. Sleep less, study more? First, what really happens at night.
2. 0:08Through the night you go round a cycle, several times. Light sleep, then deep sleep, which comes mostly early in the night. Then REM sleep, when most dreams happen. It gets longer towards morning. Your brain never switches off.
3. 0:30Sleep helps you learn and remember. It helps you fight infections. And it supports growth in children and teenagers.
4. 0:42Seventeen hours awake slowed reactions like some alcohol. Twenty four hours awake, like being drunk. A long school day can reach seventeen hours.
5. 0:56Yet the full purpose of sleep remains a mystery.
6. 1:03Before a test, count sleep as studying. And never drive after a night without sleep.
7. 1:12Sleep is not time switched off.