You may have heard that we have different sleep cycles, but why do we have them and what is happening in each phase? Find out more about what is going on in your body whilst you are asleep.
Sleep. Why do we need it? Is it just a chance to give our brains a bit of downtime? We all spend a third of our lives doing it, so what's really going on?
It seems that giving the brain some time off from managing our conscious mind is part of it. However, the brain uses this so-called “free time” to perform many necessary activities for our survival and development.
Types of sleep
Our sleep is made up of 2 types of sleep:
- Non-REM (Rapid Eye Movement) sleep, which is where our brain is quieter and slows down
- REM (Rapid Eye Movement) sleep where the brain is more active and we are more inclined to dream
Interestingly, these types of sleep have different brainwave and breathing patterns and our heart rate can change. Also, the amount of time we spend in these different types of sleep changes throughout our lives. For example, REM sleep is half the total sleeping time of infants, but drops to about 25% around the age of 10 years. As you will see later, this reflects our developmental needs at different ages.
Sleep cycles
Through a nights sleep we flip between REM and Non REM, but they are organised into 5 stages. Each of these 5 stages takes 90 - 120 minutes. This means as an adult if you sleep the ideal 7 or 8 hours a night, you will have 4 to 5 sleep cycles.
Let's have a look at what happens going through a typical cycle.
- Stage 1: Falling asleep - This is our lightest sleep as we drop off and one that is easiest to wake from. Our brainwaves slow down and physically our heartbeat slows and muscles start to relax. This is the phase where you sometime get those muscle jerks or feeling like you are falling.
- Stage 2: Lighter sleep - Compared to stage 1 it is harder to wake someone from this stage. Breathing and heartbeat slow further and our temperature starts to drop. Eye movement under the lid has stopped in this phase too.
- Stages 3 & 4: Deep Sleep - In this stage our brainwaves, breathing and heartbeat slow right down. The body is fully relaxed and we are much harder to wake.
- Stage 5: REM Sleep - This is where our brain activity is similar to when we are awake, but the body is still relaxed. There is rapid movement under the eyelids, heart rate increases, breathing is more erratic and body temperature increases.
As you can see through stages 1-4, which are non-REM stages that they are more relaxing, whereas stage 5 REM Sleep is far more active. To understand the differences further let's take a closer look.
Image credit: irunfar.com/catching-zzzs-the-science-of-sleep
What happens in non-REM Sleep?
This is our most restorative sleep and accounts for around 80% of our sleep time.
As we have seen non-REM sleep is a time when our brain waves slow, as does our heart rate and breathing. Activities in this phase include:
- Spring cleaning- When we are most relaxed our body is able to clean up the brain after a hard day of thinking. As our brain cells create energy they produce waste products that need to be cleared away. These are neurotoxic, meaning they can be damaging to brain cells if they are not removed at night.
- Growth and repair - Growth hormones are released, which enable us to grow and repair our bones, muscles, tissues and organs. Our brain cells also undergo repair and our immune function is restored at this time.
- Making hormones - On a physical level sleep is an essential time for maintaining our hormones. The hormones Ghrelin and leptin that regulate feelings of hunger and fullness are balanced at this time. Poor sleepers might struggle with this balance, which is why weight issues can occur in people who don’t have healthy sleep patterns.
Did you know?
- When we have a poor night’s sleep, we will spend longer in non-REM sleep the following night in order to catch up
- Although the muscles are relaxed people turn approximately every 20 minutes
- Bedwetting and sleepwalking occur in deep sleep
- Most nightmares occur during the deep sleep phase of our sleep cycle
- Research has linked Beta-amyloid with Alzheimer’s disease. Beta-amyloid is a protein that needs to be cleared out of the brain whilst we sleep. This is why long term poor sleep is a risk factor for Alzheimer’s¹.
What happens in REM Sleep?
REM sleep is named after the rapid eye movement which occurs during this phase of sleep.
As we have seen REM sleep is when our brain is very active; in fact, it uses more oxygen than when we are awake. Activities carried out in this phase include:
- New brain connections - It is thought that in this stage of sleep we process the day’s new thoughts, so we are actually learning and developing whilst we sleep. The brain takes this new information and assimilates this into our existing information. It then has the ability to come up new ideas. So the concept of “sleeping on it” when you need to work something out is completely valid.
- Filing our memories - The events of each day are stored in our short-term memory. Each night our brain replays the memories, removes all the distracting background noise and then saves the important information in our long-term memory. All other information is ditched, which frees up space for new memories the next day. Amazingly, the brain also reviews our long-term memory, rearranged information and removing anything that is longer necessary. This regular tidying is handy so our brain does not get cluttered up with old unnecessary information.
Did you know?
- We have more REM sleep when we are younger, as we have a more new experiences to process.
- REM sleep is thought to be when our dreams occur. The last phase of REM sleep is in the morning and is thought to be the longest. This means most of our dreaming occurs early morning.
Now knowing what goes on in our sleep, having a poor night's sleep has bigger implications than just a day feeling tired and grumpy. If you are someone who struggles with regular sleep issues you can book a time to talk to one of our in house naturopath or take a look at our range of sleep products.
Reference:
¹ https://www.the-scientist.com/news-opinion/poor-sleep-linked-with-future-amyloid-build-up-67923
