Why do we sleep?
Sleep is a biological necessity. All complex organisms have a sleep-wake cycle, from simple fruit flies to humans. In humans, sleep has many vital functions for both physical and mental health. Important experiments with individuals who were sleep deprived have shown us much about the function of sleep.
We have found out several things about sleep. Sleep helps us to modulate our body temperature. It conserves energy, maintains the correct weight and it maintains a normal immune system. The most important consequence of sleep deprivation shows up in brain function. Individuals with sleep deprivation cannot learn tasks properly because of memory disturbance. They also experience disturbances of mood. They often display behaviour with hyperactivity, irritability and impairments in attention and concentration.
So, a good night’s sleep is vital for our body and brain to work at their best during the day.
What is sleep and why is it important?
There are two distinct states of sleep. Rapid Eye Movement (REM) sleep and Non-REM sleep (which has three different stages). Each one links to specific brain waves and neuronal activity.
REM sleep is the phase of sleep in which most dreaming occurs
Intense dreaming happens during REM sleep. This is a result of increased brain activity. At the same time, paralysis occurs in the major voluntary muscle groups.
REM is a mixture of brain states of excitement combined with muscular immobility. For this reason, it is often called ‘paradoxical sleep’.
NREM sleep is most of the time dreamless sleep.
During NREM, the brain waves are usually slow and of high voltage. The breathing and heart rate are slow and regular, the blood pressure is low, and the sleeper is rather still.
Most people cycle through all stages of NREM and REM sleep several times during a typical night. Yet, the REM periods become longer and deeper toward morning.
Dream-like events that happen during NREM are much shorter than those we have during REM sleep. They are also more likely to concentrate on a single emotion.
NREM sleep consists of three stages; N1, N2, N3, each of increasing depth. Most of us cycle through the four stages of NREM ( N1, N2, N3 ) and REM sleep several times during a typical night.
Sleep progresses in these ‘sleep cycles’ from N1 through to REM. Each sleep cycle lasts approximately 90 to 110 minutes for adults. The first couple of sleep cycles have long periods of uninterrupted stage N3 sleep. This is also known as Slow Wave Sleep (SWS), with relatively short REM periods. Later in the night, the REM periods lengthen and SWS is often absent. So, the first third of the night is mainly SWS sleep. And the latter part of the night we spend in the lighter stages: N2 and REM sleep.
We all wake up several times during the night and that’s normal. In spite of popular belief, good sleepers don’t ‘sleep all the way through’ the night. At the end of each sleep cycle, we all wake up for a short time. Most people won’t remember that, but we all do. When we become more aware of these awakenings and start to worry about them, they could become a problem. When you become aware of being awake for long periods during the night then you might have a sleep problem. You then might want to seek help for that.
Stage N1 (1-5% of sleep) is the lightest stage of sleep and is the transition between wake and sleep. You enter sleep via stage N1, whenever you fall asleep. This is the kind of sleep that you experience when you are drifting in and out of sleep, especially at the beginning of the night.
When you are in stage N1 sleep, it is easy to wake up. If you are awake, you might claim not to have been asleep at all, as we’re often not aware of this stage of sleep.
Falling asleep is not like switching off a light bulb. Some people experience sudden muscle contractions or ‘jerks’ during the transition from wake to sleep. Others notice a sensation of falling or a ‘presence’, benign or otherwise, in the room. There are some complex processes that need to occur while entering sleep. And these, so-called ‘hypnagogic’ events seem to be glitches in the process. Although they may feel as worrying or scary, they are in fact normal and harmless.
Stage N2 accounts for approximately 45-50% of sleep. And although it is the longest single part of sleep, it is also the stage which we know least about. It plays a part in memory, but we do not yet quite understand why we spend half the night at this stage.
As sleep becomes deeper, slow brain waves (called delta waves) start to appear, and we enter N3 or SWS (20-25% of sleep). N3 is the deepest stage of sleep, and when someone is in SWS, it can be very hard to wake them up. SWS takes care of the restorative processes of sleep and is thus the part of sleep that causes you to feel like you have had a good sleep. It also plays a crucial role in making you feel well-rested and energetic during the day. SWS is vital for memory and learning and this is why children experience much more SWS than adults.
Another reason why children have more slow-wave sleep (SWS) than adults is that this is the only stage of sleep in which we physically grow. Some people, particularly children, experience behaviours known as ‘parasomnias’ during SWS. These are things like bed-wetting, sleep talking, sleepwalking or night terrors.
Regardless of sleep need, the amount of slow-wave sleep we get remains rather stable. Both short and long sleepers essentially have the same amount of SWS. Scientists came to the conclusion that this means that we need a minimum amount of N3 deep sleep per night, no matter how long the total sleep time. Because SWS is so important, it is obvious why, after one night of partial or complete sleep deprivation, the brain tries to make up all the missing SWS. This gives us a feeling of sleeping more soundly following a period of sleep deprivation.
During Rapid Eye Movement (REM) sleep (20-25% of sleep) the eyes are moving quickly back and forth under closed eyelids, hence its name. It is during REM sleep that most of our ‘story-like’ dreams occur. Dream-like events can happen in any stage of sleep, but dreams that we have outside of REM sleep are often thought to be shorter. They are more focused on one emotion and do not have the narrative complexity of dreams in REM sleep.
It is during REM sleep that we process emotional memories and ensure our psychological health. During REM, our brainwave activity can increase to levels that are similar to when a person is awake. Breathing becomes more rapid, irregular and shallow, heart rate increases and blood pressure rises. To stop us from acting out our dreams, we lose muscle tone during REM and are effectively paralysed. It happens often that we wake up during REM sleep.
If we don’t get enough sleep our physical and mental health suffers.
Individual sleep need is like height – we are all different, and it is, to a large degree, genetically determined. Anywhere between four and eleven hours is thought to be normal. Getting only one hour less sleep a night than you need, can have measurable effects on your physical and mental health. And this cumulative lack of sleep can have long-term and serious health consequences.
If you feel sleepy during the day, you are probably not, for whatever reason, getting the sleep you need during the night.
You know that lack of sleep can make you grumpy and foggy. But you may not know what it can do to your sex life, memory, health, looks, and even ability to lose weight.
Here are 10 surprising — and serious — effects of sleep loss.
Lack of sleep:
- Causes Accidents
- Dumbs You Down
- Can Lead to Serious Health Problems
- Kills Sex Drive
- Is Depressing
- Ages Your Skin
- Makes You Forgetful
- Can Make You Gain Weight
- May Increase Risk of Death
- Impairs Judgement, Especially About Sleep
So, get yourself a good night’s sleep, it is much more important for you than you might have thought before. Next week we will go deeper into the 10 effects on your health and the week after that we will discuss how you can get the most out of your sleep and how you can improve on your sleep.
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