Sleep. Something we all do and are all familiar with. Whether we are an 8 hour a night person or refreshed with less, we all need it. It is essential to our survival.
Scientists think that pretty much every land dwelling mammal experiences sleep. Even dolphins sleep – although with half their brain at a time, which is a rather clever way of them staying alert enough to avoid predators and stay afloat to breathe.
Scientific studies mean we now know a bit more about sleep and why it is important, although there is still a lot that we do not know. Why we need daily sleep is still not certain for example.
So what is sleep all about and why do we need it? Let’s start with a little bit of science…
How has our sleep evolved from apes?
On the face of it, sleeping presented a significant predatory threat for our ancestors. These lesser apes used a precarious, balancing act to sleep in trees and avoid predators and so did not sleep for long periods at a time. Scientists believe there is a link between intelligence and sleep patterns as the apes evolved.
As apes adapted to sleeping in more protected, safer spaces with less threat from being eaten, so they could experience longer periods of quality sleep. This increase in quality sleep is thought to be key in the evolution of brain function and therefore intelligence, from lesser apes to great apes and eventually humans.
As a species, we evolved our sleep patterns to needing shorter amounts of quality sleep per day than our ape ancestors, leaving more time to focus on other things, for example learning, developing socially and protecting ourselves. Although, interestingly we haven’t yet evolved beyond the need for daily sleep.
Why we sleep
Studies show that sleep is more than resting and re energising, although this is part of it, both physically and mentally. When you sleep, there is a lot more going on, maybe more than you realise.
Whilst you are unconscious and your body is still, your internal biological systems are very busy cleaning up after the day’s activities. There are biochemical toxins that need removing, cells to be replaced and damaged tissues to be repaired. All this activity helps to boost your immune system and recharge you physically ready to face another day.
It is easy to think about your physical need to recharge and relate this to your musculoskeletal system (the effort of your muscles and bones working together). I am sure we have all felt physically tired where, in the extreme, our body is drained of all energy and we need to sleep to recover. However, maybe a less obvious part of your physical restoration involves your heart and cardiovascular system. You could think of this as the fuel pump of your body supplying oxygen and energy to your cells and although it continues to work whilst you sleep, it is at a reduced rate. This too needs to recover and rest, in order to face a new day.
Sleep is essential for re energising us emotionally and mentally as well as physically. Just as we get physically tired, we can get emotionally tired and need to recover. During sleep, studies show that our brain not only controls our biological restoration, but also makes sense of the memories and information gained from our daily experiences. These need ‘filing’ into long term memory systems and ordering so we can make sense of the learning in the future and gain perspective. It seems there is some scientific evidence in the phrase my mum used to use when I was younger:
‘Get a good night’s sleep. Things will seem better in the morning.’
This whole restoration process is thought to go some way to explain why children and teenagers sleep more than adults; it makes sense that the sponge-like learning of young children and vast physical growth would require more restorative energy and time.
What is sleep
You may have heard about different stages of sleep, REM (rapid eye movement) nonREM, quality sleep, dreaming sleep, deep sleep. Scientists now better understand the main phases and the cycle of sleep and typically the diagram below shows what happens:
Stage 1: Easily woken, can experience sudden jumps due to muscle spasms. Eyes move slowly and muscle activity slows.
Stage 2: Brain waves slow and body temperature cools.
Stage 3: Deep sleep. Harder to wake. If woken now will feel groggy and disorientated. No eye movement or muscle activity.
Stage 5: REM. Breathing changes, it increases and is more irregular and shallow. Eyes move rapidly, flickering from side to side. Muscles on limbs are paralysed. Heart rate and blood pressure increase. We dream in REM sleep.
- The first REM cycle occurs 70-90 minutes after falling asleep.
- The first sleep cycle has less REM sleep and longer deep sleep.
- REM sleep increases through the night and deep sleep reduces.
- In the morning we spend nearly all of our sleep time in stages 1,2 and REM.
More fun sleep facts
- When in the first stage of sleep we are less likely to respond to noises although we are still likely to wake if hit (unsurprisingly!)
- In this first stage of sleep it is common to experience muscle spasms or jumps and a sense of falling.
- As adults we typically need 7-9 hours of sleep a night and although we can function on less we perform less well with reduced reaction times, poorer judgement and lower ability to manage appetite.
- Humans are the only mammal to willingly put off going to sleep.
- Regular exercise helps with falling to sleep and quality sleep patterns. However, exercising close to bedtime can make falling to sleep more difficult.
- Giraffes only need to sleep for less than 2 hours a day.
- Humans sleep for about one third of their life… cats, two thirds.
- 11 days is the longest known period without sleep.
- It takes about 7 minutes for the average person to fall asleep.
- Snoring is the biggest disrupter of sleep.
How much sleep do we need?
I know I am glad I am not a giraffe because I definitely need more than 2 hours a night!
Sleep patterns and needs are controlled through hormones and whilst there are similarities from person to person, our sleep pattern is individual to each of us. The amount of sleep we need is also impacted by life stage and other factors, for example our health.
We all know that babies, young children and teenagers sleep more than adults. (Although babies sleep can be more erratic with them waking when we typically want to sleep). This relates to the higher levels of growth and learning for children as they develop.
The idea that we need less sleep as we get older is a myth. Older adults still need an average of 7-8 hours a night too although, again as their daily routine changes how frequently they sleep may alter.
We sleep more typically when we need to recover and rest. I am sure any mums reading this will remember the real need to sleep during the first 12 weeks of pregnancy. I recall this feeling being all consuming and not being able to move past it.
I can also relate to this need when recovering from a back injury. Whilst some of that sleep may have been drug induced, my body also recognised the need to sleep to heal itself and I managed lots more than the average 7-9 hours per day. Again an increase in average daily sleep is common if we are unwell.
Whatever your sleep pattern, quality sleep is as essential to us as food and water. Even small amounts of sleep deprivation or disruption can have a significant impact on our health and wellbeing. We will be exploring more in this series on sleep, including signs you are not getting enough sleep and some things to think about to improve the quality of the sleep you do get.
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