What Are the Stages of Sleep?March 26, 2021
Why we sleep is still much of a mystery to science and maybe failing to get the full picture of sleep is why many of us still experience a lack of sleep.
Around 35% of American adults sleep less than seven hours per night, and another 10-30% suffer from insomnia. Poor sleep quality increases the risk of sleep disorders or other problems such as cardiovascular disease, high blood pressure, depression, diabetes, and more.
However, simply sleeping is not enough. The brain has to go through several stages of sleep in order to feel completely rested and rejuvenated again. In this article, you’ll learn about the details of our sleep stages, what we know so far about the brain during these stages, and why we need them.
How Do We Sleep? Three Important Brain Parts
Sleep is a particularly important part of our lives. Our brains are continuously working throughout the day, making decisions, and guiding us through our everyday lives.
When we sleep, the brain rests. This allows it to form crucial neurological pathways, create new memories, and retain or learn new information. That’s why sleep deprivation leads to difficulty concentrating and maintaining a balanced life.
Sleep is a complicated cycle that involves several parts of our brain, and each contributes to a good night’s sleep.
Without three critical neural areas, and the body’s circadian rhythm, we would not be able to get quality sleep or even sleep at all. Let’s take a look at the role of each brain’s three regions for sleep.
The Circadian Rhythm
The circadian rhythm, otherwise known as our internal body clock or master clock, controls the sleep cycle. It’s tied to light exposure, which enables us to understand when we have to be awake and when we have to sleep.
People with disrupted circadian rhythms experience severe disruptions to their sleep cycle, or sleep disorders such as insomnia and sleep deprivation.
The hypothalamus is a structure about the size of a peanut, and it’s located really deep into our brains. Within the hypothalamus, a cluster of cells called the Suprachiasmatic Nucleus (SCN) receives information about light exposure into our eyes.
A person with damage to their SCN would have difficulty distinguishing between light or dark. This would lead to erratic sleep or poor-quality sleep. Even blind people still retain some sense of light due to a well-functioning SCN.
The Brain Stem
The brain stem and the hypothalamus work together to control our sleep and wakefulness states. Without this connection, we would have difficulty maintaining the balance and distinguishing between these two states. The brain stem also releases chemicals that make our muscles relax, so we don’t act out our dreams in REM sleep.
This part of our brain controls whether we hear the outside world during sleep or not. During most stages of sleep, your thalamus is quiet. This allows you to to tune out external noises and get a good rest. However, during REM sleep, the thalamus becomes active with different sounds, images, and sensations for your dream state.
What Are the Types of Sleep?
The sleep cycle varies from one person to the other. Even in one individual, sleep is not uniform and it depends on several environmental factors. During the night, a person’s sleep cycle is made up of different types of sleep, each with sleep stages.
Non REM Sleep
REM stands for rapid eye movement. During non REM sleep, your body relaxes, and your brain activity decreases. This is also known as quiet sleep and is made up of different stages of sleep.
During non REM sleep, your body can repair tissue, build bone and muscle, and strengthen the immune system. Younger people go through a more extended period of non REM sleep than older people, so this stage does change with age.
Rapid eye movement or REM sleep, happens later in the sleep cycle. When we are in REM sleep, our sleep cycle and brain are active again. During REM sleep, your eyes move rapidly, and this is when you have most of your dreams.
Because of such an intense dreaming period, your body is temporarily paralyzed, so you cannot act out those dreams. During rapid eye movement REM sleep, your body and brain restore themselves, create new memories, and integrate learning.
Both of these types of sleep are paramount for our well-being. We tend to shift from one to the other during our sleep cycle, but REM sleep usually occurs in the morning.
What Are the Four Sleep Stages?
Everyone sleeps differently, but a typical person goes through four to six sleep cycles or sleep stages. During these stages of sleep, a person goes through non REM sleep and REM sleep. Each stage might last an average of 90 minutes.
Here are the four most common stages of sleep in order of occurrence. The first three are stages of non REM or NREM sleep, and the final one is REM sleep.
Entering the Sleep Cycle
As you are falling asleep, the heart rate starts to slow down, and you start relaxing. You feel like you are in between sleep and wakefulness, and you experience different brain waves, like beta and alpha brain waves. You might also experience some strange sensations while you're falling asleep.
These include hypnagogic hallucinations, which is that jolting sensation of falling and hitting the ground, or feeling like someone just called your name. Other sensations include the myoclonic jerk, which is when a person is suddenly startled for no reason at all.
These sensations suggest that the person is starting to fall asleep but do not necessarily constitute an actual sleep stage.
Non REM Sleep Stage 1
During the NREM sleep stage 1, a person is dozing off. Your brain activity starts slowing and emits slow brain waves or theta waves, your heart rate starts decreasing, but your body isn’t completely relaxed.
This sleep stage lasts only 5 to 10 minutes, and if you wake the person up during it, they may say that they were not sleeping because it doesn’t feel exactly like sleep. But, if left undisturbed, the person might move quickly from stage 1 to stage 2.
Non REM Sleep in Stage 2
The NREM stage 2 sleep is also known as light sleep. During this stage, the body temperature drops, while breathing and heart rate become more regulated. The brain is in a more rested state, and you are unaware of your surroundings. Your brain activity is quick and emits faster waves known as sleep spindles.
The non REM stage 2 sleep lasts for around 20 minutes but is repeated many times throughout the night. The American Sleep Association reports that we spend a lot of time in this stage, so about 50% of our total sleep time in stage 2 sleep.
Non REM Sleep in Stage 3
The third stage of sleep, or the NREM stage of sleep 3, is also called the period of deep sleep. Because your brain emits delta waves, this is also called delta sleep.
Delta sleep, or NREM sleep stage 3, is one of the sleep stages that makes you feel refreshed in the morning and usually occurs during the first half of the night.
During these sleep cycles, your heart rate and breathing are very slow, your body temperature starts decreasing, and you are so relaxed that it would be difficult to wake you. Your brain emits slower delta waves, and your blood pressure is also lower than average.
Deep sleep is restorative, and it may help your immune system. Studies show that non rapid eye movement in sleep stages 3 contributes to creativity and memory.
REM sleep is the stage of sleep for dreaming. During this stage of sleep, your body is temporarily paralyzed while your heartbeat quickens and eye movements are rapid, which is where this stage gets its name from.
REM sleep is believed to occur about 90 minutes after you fall asleep. According to the American Sleep Association, we spend about 20% of our sleep time during this stage.
REM sleep can also be considered deep sleep but is just another form of deep sleep. This stage of the sleep cycles is essential for memory restoration, learning, and creativity.
What Affects the Stages of Sleep?
Different factors can affect sleep and the stages of sleep a lot. Poor quality sleep, and sleep disorders such as sleep apnea can trigger if a person doesn’t go through each sleep stage properly or fails to sleep completely.
Here are the four most common factors that affect the sleep stages.
Sleep is just as important for our survival as food and water. Without sleep and going through the proper sleep stages, we feel tired and have problems concentrating or responding. Severe sleep deprivation could lead to even more severe problems with memory and general wellbeing.
People should generally go through at least four to six sleep cycles, including non REM sleep in three stages and REM sleep for one stage. Each stage could be repeated several times for good sleep quality. There are also several ways you can promote better sleep hygiene, including reducing your light exposure before bed and putting digital devices in another room.
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