What is sleep?
It might look like you’re doing nothing when you’re asleep, but your brain is actually putting in a lot of work as your body rests. Studies have shown that the brain is as active during sleep as it is during the day. Temperature, blood pressure and most body functions decrease overnight. But the brain keeps charging!
YOU’RE FEELING SLEEPY
Sleep and wakefulness are thought to be controlled by two independent but interacting systems in your body. Your circadian rhythm, or body clock, controls when you feel tired and go to sleep and when you wake up. And a self regulating or homeostatic process tracks how much sleep you need. The two systems interact to control when you fall asleep and how long you sleep for.
SLEEP STAGES
Sleep takes place in recurring cycles that last for 90-110 minutes in an adult, but are much shorter (around 45 minutes) in a baby. Each cycle is made up of five stages. The first four stages are non REM sleep and the fifth stage is REM sleep.
Stage 1: Non-REM – Light sleep
In this stage you’re only half asleep and can be easily awoken. Your muscle activity slows down and you might get some twitching. This stages lasts for about 10 .
Stage 2: Non-REM – True sleep
Your heart rate and breathing pattern starts to slow down in this stage which lasts for around 20 minutes.
Stage 3 & 4: Non-REM – Slow wave sleep
As you move into Stage 3 your brain begins to make delta waves and your breathing and heart rate really slow down. In Stage 4, breathing is very regular and you’ll be very still. It’s very hard to wake up at this stage and if you’re woken up you may feel very groggy and disoriented. Sleep walking, night terrors and bedwetting can occur in this stage.
Stage 5: REM sleep
This stage kicks in about 70 to 90 minutes after falling asleep. Brain activity spikes during this period – it’s often more active than when you’re awake! Most dreaming takes place in this stage. Your eyes will flutter (hence the name, REM - Rapid Eye Movement) and your breathing will be irregular. Thankfully, your brain will also tell your muscles to be immobile so you don’t act out your dreams!
WHY DO WE SLEEP?
Scientists aren't really sure why we sleep, but they do know that we need sleep to function and for optimum health. Like hunger, thirst and sexual desire, the need for sleep is strongly wired into our biology. And we're not alone. While there is huge variation in the amount of sleep required by different animals, we all seem to need some shuteye - even fruit flies! So what does a good night snoozing in bed achieve? You may think you're rejuvenating your body, but that doesn't seem to be the case. Most bodily functions keep on going while you sleep, and while muscles require periods of relaxation, they don’t seem to need you to be asleep. It's the brain which seems to benefit most from sleep.
Sleep researchers are still working out the ways that sleep affects our brains. Does sleep allow us to deal with the information the brain received and processed whilst awake? Or does it allow the brain to regulate itself, like a nightly cleanup? Another idea that is becoming more popular is that sleep - especially slow wave sleep - helps us to store memories and master various skills. (See "The meaning of dreams" ABC Science feature)
While scientists aren't exactly sure of how sleep benefits us, they do know there are clear negative health outcomes associated with inadequate sleep. Lack of sleep is linked to numerous physiological and psychological health issues, such as type 2 diabetes and depression. Being sleep deprived also results in poor concentration, irritability, daytime drowsiness and affects your immune system. Some very serious accidents, like the Challenger space shuttle disaster, have been linked to sleep deprivation.
HOW MUCH SLEEP DO YOU NEED?
Adult humans sleep on average around 7 hours a day - three hours less than other primates like chimps, rhesus monkeys and baboons, but much more than elephants, who only need about three hours, and much, much more than giraffes, who need less than two hours.
However, there's a large variation in the amount of sleep that people need, ranging from less than 6 hours to more than 9 hours. People at all points within this range show no real difference in health and waking performance. There may be a genetic basis to this variation – short sleepers and long sleepers are found to run in families.
Rather than detailing set amounts of prescribed sleep for each age, sleep researchers these days tend to provide a general range and suggest that you use your judgement in working out if you're getting enough sleep. If you feel sleepy straight after waking up, or you have trouble paying attention during the day or you fall asleep within a few minutes of going to bed, well, you probably need to sleep for longer.
