We used to view sleep as a passive activity during which the body and brain stay dormant. Thanks to scientific research we now know differently. The stages of sleep describe a period during which the human body is far from totally “zonked out”. It is engaged in a number of activities necessary to a healthy life. Although they are not conscious, human bodies experience a series of well-defined transformative processes during the night.
A normal sleep cycle is required predominantly to maintain healthy brain functions. The brain’s ability to adapt to input, known as plasticity, depends on having time off-line. This allows the brain to process what we’ve learned during the day and prepares us for learning new things the following day. Being unconscious at the end of the day may also help remove waste products from brain cells. Brain function is only one benefit of healthy sleep, though. Poor sleep has been linked to symptoms of depression, seizures, high blood pressure and migraine. Poor sleepers are more likely to be obese and have type II diabetes than healthy sleepers.
If you’ve ever wondered what happens when we sleep, you’ll find the answer here. By understanding healthy sleep cycles and maintaining the right patterns at night, you can greatly improve your health and wellbeing.
What is a Sleep Cycle?
The stages of sleep are intrinsically linked to our circadian rhythms. Circadian describes the cycle of activities living organisms undertake over a 24-hour period. These are generally driven by our relationship to light, dark, day and night. Our bodies know it’s time to rest because it is dark and we feel tired.
When you are sleeping, however, the cyclical behaviour continues through four main phases during the night. Firstly you transition from wakefulness to sleeping lightly. Then you slip into deep sleep and, finally, you dream. This four-stage cycle was adopted in 2007 by the American Academy of Sleep Medicine (AASM). They also labelled each stage as Non-REM and REM variants.
What Does REM Stand For?
REM stands for Rapid Eye Movement. This is used by sleep science to determine which stage of the cycle a person is at any given time. In the first three of the four different stages of sleep, labelled Non-REM, the eyes remain still and closed. They will feel familiar as they cover drifting from initially closing one’s eyes to falling fast asleep. The fourth, the REM stage, sees a person’s eyes move rapidly while closed. Their brain activity, breathing, heart rate, and blood pressure increase too. Muscles in the arms and legs become temporarily unable to move. This final phase is considered the deepest and is often associated with dreaming.
Non-REM Stage 1
This first stage of sleep is, perhaps unsurprisingly, the lightest. It is the transition phase between wakefulness and unconsciousness. It usually lasts no more than 15 minutes and you can easily awaken from it if interrupted. At this time, the brain produces small and fast beta waves that indicate the brain is pretty much still active and engaged with your surroundings, even if you are not conscious of it.
Non-REM Stage 2
This second phase is often described as light sleeping. It usually lasts 20 minutes and sees your heart rate slow and body-temperature drop. Brain waves change too. They become shorter and faster, in so-called spindles. These are thought to be a feature of memory consolidation. During stage 2, it seems, your brain gathers, processes, and filters new memories.
Non-REM Stage 3
By this stage, you’re in a deep sleep. Your body is fully relaxed and your blood pressure is low. You are likely to sleep through slight noise unaffected. Brain waves have become long and slow delta waves. In fact, this stage is sometimes known as delta sleep. This type of brain activity is associated with ‘declarative’ memories including learning facts, figures and general knowledge. It is during this stage that your muscles completely relax and repair too.
REM Sleep Stage
This stage is associated with the deepest of sleep and occurs approximately 90 minutes after you’ve initially drifted off. This doesn’t stop your brain from becoming incredibly active. In fact, it closely resembles daytime levels of activity.
Your body remains catatonic except for your eyes which rapidly move too, although not connected to the visual part of your brain. Your breathing becomes faster and more irregular.
It is this stage that leads to dreams and, occasionally, sleep talking and walking. It is thought that REM stage is when emotions and emotional memories are processed and stored.
How Does The Body Regulate Sleep?
In order to gain a sleep explanation in detail, we need to consider two of our body’s main systems.
Sleep-Wake Homeostasis is the medical term for feeling tired. The longer we’re awake, the more we need a break. Our homeostatic drive builds the pressure we feel to sleep based on how long we are awake. The Circadian Alerting System describes your body’s biological 24-hour clock. It plays a central role in numerous biological processes including appetite, energy and sleep. It is how we know it’s daytime when we should be awake, and nighttime when we should be sleeping.
These two body systems work in harmony, along with our brains, hormones and neurotransmitters, so we know how much sleep we need and when we should have it.
To date, research into the science of sleep still hasn’t fully uncovered the intricate and complex processes that occur in our bodies to help us stay healthily.
Why is Sleep Important?
Healthy sleep is the change of consciousness that our body needs to repair itself each and every day. It is characterised by entering our subconscious, limiting interactions with our surroundings and keeping us quiet and still.
As we’ve established above, the brain is active to varying degrees during the night. The study of brain waves has indicated sleeping brains continue to carry out important functions around memory and learning.
Sleep affects our mental and physical well-being including our ability to fight disease.
What Happens If You Don’t Sleep?
The symptoms of poor and interrupted sleep go beyond obvious tiredness. Brains which have not had a chance to recuperate properly overnight find taking in new information, learning new things and making decisions challenging. Poor brain function leads to stress, emotional problems, depression and fatigue. Poor sleep has been linked to physical symptoms including cardiovascular problems, weakened immune systems, obesity and Type II Diabetes.
It is definitely worth investing time in understanding your sleep routine and, if you are worried, discussing the issues with your doctor.
How to Have a Healthier Sleep Cycle
There are many tips to maintaining a healthy cycle that takes in all four of the required stages described above. Firstly, create and stick to a schedule that gives you the sleep you need. For most adults, this means 8-hours a night. Eat well during the day. Avoid stimulants and hitting bed feeling hungry or over full. You can help healthy sleep by setting up your bedroom to create a restful environment. This might mean keeping electrical devices and smartphones away until morning.
The other ways to help sleep are to be active during the day and reduce stress so your mind can settle. We, therefore, recommend some form of physical exercise during the day and you might enjoy adding some relaxation techniques to your routine at the end of the day.
If your sleep is being more seriously affected, it might be worth consulting your doctor or a medical professional. Letting your body recover and recuperate each night properly is vitally important to your wellbeing.