What is sleep?
Definition of Sleep: "The natural periodic suspension of consciousness during which the powers of the body are restored."
Types of sleep
There are two main types of sleep:
Rapid Eye Movement (REM) sleep
Accounts for 20% of total sleep time. During REM sleep, our brain is very active, our muscles are very relaxed, our eyes move quickly from side to side and we dream. REM sleep functions:
- Nervous fatigue recovery
- Organisation and incorporation of acquired knowledge (memory) and
- withdraw of useless information.
Accounts for 80% of total sleep time. The brain is quiet, but the body may move around. Hormones are released into the bloodstream and our body repairs itself after the wear and tear of the day.
There are 4 stages of non-REM sleep:
Pre-sleep - The muscles relax, the heart beats slower and body temperature falls.
Light sleep - we can still be woken easily without feeling confused.
Slow wave sleep - our blood pressure falls, we may talk in our sleep or sleep walk. This is also the stage in which such parasomnias as night terrors, bedwetting and teeth grinding occur.
Deep slow wave sleep - we become very hard to wake. If we are woken, we feel confused.
- Non-REM sleep functions:
- Restoring physical energy
- Increasing immune functions
- Producing protein and glycogen
- Secreting hormones such as prolactin and growing hormones.
We move between REM and non-REM sleep about five times throughout the night, dreaming more as we get toward the morning. During a normal night, we will also have short periods of waking.
These last 1 or 2 minutes and happen every 2 hours or so. We aren't usually aware of them. We are more likely to remember them if we feel anxious or there is something else going on - noises outside, our partner snoring etc.
The different sleep stages
Night sleep consists of several 90-minute cycles repeated 4-5 times each night. Each cycle includes 5 stages:
Stage 1: Fall asleep
Stage 2: Light sleep (NREM sleep)
Stage 3: Deep Sleep (NREM sleep)
Stage 4: Deeper Sleep (NREM sleep)
Stage 5: REM Sleep
How much sleep do we need?
This depends mainly on how old we are.
- Babies sleep for about 17 hours each day.
- Older children only need 9 or 10 hours a night.
- Most adults need around 7-8 hours sleep each night.
- Older people need the same amount of sleep, but will often only have one period of deep sleep during the night, usually in the first 3 or 4 hours, after which they wake more easily.We also tend to dream less as we get older.
There are also differences between people of the same age.
Most of us need 7-8 hours a night, but some (a few) people can get by with only 3 hours a night. It's not helpful to regularly sleep more than 7-8 hours each night.
The short periods of being awake feel much longer than they really are. So it's easy to feel that we are not sleeping as much as we actually are.
Having enough sleep means going about one's business until the end of the day without feeling drowsy. If you push the snooze button of your alarm clock every morning, you may require additional minutes (hours?!) of sleep.
Remember: If we are not getting enough sleep, we find our brains struggling to cope, our memory slipping, our concentration below par, our muscles fatigued, our skin dull and our eyes lack-lustre.