Sleep is vital for the proper functions and survival of the human body. Improper sleep patterns make the body vulnerable to various health problems such as insomnia, sleep apnea, depression, anxiety, etc. Therefore, quality sleep is essential to keep the body in good health. For a better understanding, it’s necessary to know about the different stages of sleep cycle.
How many stages of sleep cycle are there?
According to the American Academy of Sleep Medicine(AASM), there are four different stages of sleep cycle. Each sleep cycle differs both in duration and quality. All of the stages of sleep cycle are necessary for the proper functioning of the brain.
The first three stages of sleep are parts of non-rapid eye moment(NREM) sleep, while the fourth stage is rapid eye moment(REM).
Each stage of the sleep cycle is associated with a specific role in proper brain function and has significant importance. The entire sleep cycle repeats itself several times during sleep at night. With each successive turn, the cycle increase in both duration and depth of sleep.
Do you know an average human being spends 26 years of life sleeping? That’s equal to 9,490 days or 227,760 hours. While 7 years of trying to get sleep. It means 33 years or 12,045 days spent in bed!
NREM Sleep Cycle
It is divided into three different stages of sleep, which are listed below.
NREM Stage 1
It is the first and shortest stage of sleep. It lasts for a short duration of one to five minutes. It is also referred to as the “light speed stage” because it involves a transition state between sleep and wakefulness.
A sleeping person can wake up quickly without any groggy effects. In this stage of sleep, the body is not fully relaxed yet, but it starts to calm down. It prepares itself and starts to slow down the body and brain activities. Heartbeat, breathing, and eyes movement also slow down gradually.
During this stage of the sleep cycle, the brain release theta waves, high amplitude slow brain waves, which are produced in the frontal lobe of the brain.
From this light sleep, a person proceeds into the second stage of the sleep cycle if left undisturbed.
Short naps are mostly recommended, because once you enter the later stages of sleep; it becomes difficult to wake up and the person may also suffer from irritation and grogginess.
NREM Stage 2
In this stage, the body enters into a more relaxed state. The second stage also involves:
- Decreased body temperature
- Slow heartbeat and
- Lower breathing rate
- Eyes movement stop
- Reduced brain activity
- Muscle relaxation
Sleep spindles are brain waves that appear on ECG. This outburst of brain waves is present in all three stages of the NREM cycle but is more active and evident in stage 2 of the NREM sleep cycle. Sleep spindles show that the person has fallen asleep.
These spindles are involved in:
- brain plasticity
- Integrating memories
- Processing learning
- Diminishing response to external stimuli while sleeping
Stage two of the sleep cycle lasts for about 10 to 25 minutes. According to the sleep foundation, half of the sleep cycle is spent in the NREM stage.
NREM Stage 3
Deep sleep is the 3rd stage of the sleep cycle. This phase is referred to as “deep sleep” because the person gets into a deep sleep. The person becomes resistant to any external environmental stimuli, and it becomes difficult to wake up the person in this stage of the sleep cycle. We spend almost 20 to 40 minutes of sleep in the deep sleep stage.
Following events occur during this stage of sleep:
- Muscles relax completely
- heartbeat decreases
- Breathin rate further drops
- Body progress in deep sleep
Related: Importance of good sleep
Significance of NREM stage 3
In this stage, the brain shows the specific pattern of slow delta waves. Therefore, it is known as” delta sleep or slow-wave sleep.” Slow-wave sleep bolsters the immune system and contributes to critical thinking, memory making, learning, reasoning, and creativity. During this stage, that body performs most of the physical repair functions.
REM Sleep Stage
In this stage of sleep, the eyes show quick movements, although they are closed. Hence, this stage is called “rapid eye movement sleep(REM).” This stage has more similar brain activities to those of a wakeful brain.
Events that occur during this stage are:
- Breathing rate increases
- Blood pressure elevates
- Eyes movement becomes visible
- The brain’s activity enhances
- Muscles become more relaxed or even paralyzed
Significance of REM sleep stage
It is during this stage that we get dreams. Therefore, this stage is vital to dreams.
All the muscles except the eyes and breathing suffer atonia in this stage. Atonia is temporary muscle paralysis. It is thought to be good because it prevents the body from moving during sleep REM sleep has significance in cognitive brain functions.
This stage does not start before 90 minutes of sleep. The REM stage of the sleep cycle then lasts for 10 to 60 minutes. According to the sleep foundation, about 25% of sleep is usually spent in the REM sleep stage.