Journey through the Night: The 4 Stages of Sleep
As you doze off, your brain goes through a sequence of four sleep stages, with the first three classified as non-rapid eye movement (NREM) sleep or “quiet sleep,” and the fourth as rapid eye movement (REM) sleep, also called “active sleep.” Here is a journey through the night: The 4 Stages of Sleep
Understanding the role of each sleep stage is crucial for maintaining optimal cognitive function and physical health.
From repairing the body to preparing for the day ahead, each stage serves a unique purpose. In this article, we explore the four stages of sleep, delving into what happens during each phase and what can disrupt a good night’s rest.
NREM Stage 1
NREM stands for non-rapid eye movement, which refers to the first three stages of sleep. During NREM sleep, brain activity slows down, and the body is in a state of rest and repair.
The initial stage of the sleep cycle is a transitional phase between being awake and falling asleep. If someone were awakened during this stage, they might not consider themselves as being asleep.
In the first stage of sleep:
- Your brain activity slows down
- Your heartbeat, breathing, and eye movements decrease in speed
- Your muscles relax, and you may experience occasional twitches.
This initial phase of sleep typically lasts for a short duration of around five to ten minutes. During this time, the brain remains somewhat active and produces high-amplitude theta waves. These slow brainwaves mainly occur in the frontal lobe of the brain, leading to a decrease in brain activity.
Additionally, the body begins to relax, with slowed heartbeat, breathing, and eye movements, and muscles may occasionally twitch.
NREM Stage 2
The American Sleep Foundation reports that NREM stage 2 accounts for around 50% of a person’s total sleep time and typically lasts for about 20 minutes per cycle.
In stage 2 sleep, your awareness of your surroundings decreases, and your body temperature drops. Your eye movements stop, and your breathing and heart rate become more regular.
During stage 2 sleep, the brain produces bursts of rapid, rhythmic brain wave activity, known as sleep spindles, which are believed to aid in memory consolidation.
At the same time, the body temperature drops, eye movements stop, and breathing and heart rate become more regular.
This stage lasts for about 20 minutes per cycle, and prepares the body for the deep sleep stages of NREM stage 3 and REM sleep, during which the brain and body undergo repair, restoration, and resetting for the next day.
NREM Stage 3
In NREM stage 3 sleep, also called delta sleep, the brain produces slow delta waves, which are associated with deep sleep.
During this stage, individuals are difficult to wake up, even with environmental noises or activity. Sleepwalking commonly occurs during this stage, particularly in the early part of the night’s sleep.
Sleepwalking is more frequent in children and young adults compared to older adults.
During NREM stage 3 sleep:
- Muscles are completely relaxed.
- Blood pressure drops and breathing slows.
- You progress into your deepest sleep.
During this stage of deep sleep, your body undergoes physical repairs that contribute to feelings of refreshment the next day.
The brain also consolidates declarative memories during this stage, which includes general knowledge, facts or statistics, and personal experiences that you have learned.
This process helps to strengthen these memories and store them in long-term memory.
Stage 4: REM Sleep
REM (Rapid Eye Movement) sleep is the fourth and final stage of the sleep cycle. This stage is marked by rapid eye movements, hence the name. It typically begins about 90 minutes after you fall asleep, and each cycle of REM sleep can last from a few minutes up to an hour.
During REM sleep, the body experiences muscle paralysis while the brain remains highly active, almost at the same level as when you’re awake.
This is the fourth and final stage of the sleep cycle. The muscle paralysis is a natural mechanism that prevents the body from physically acting out vivid dreams that occur during this stage.
REM sleep, which commences around 90 minutes after sleep onset, is characterized by the following:
- Increased brain activity
- Muscle relaxation and temporary paralysis
- Faster and irregular breathing
- Rapid eye movements
- Dreaming
REM sleep, like stage 3, is also associated with memory consolidation. However, research suggests that REM sleep is particularly important for the processing and storage of emotional memories and emotions.
During this stage, the brain also solidifies information into memory, making it a crucial stage for learning.
Repair Work in Progress
Deep sleep, which includes stage 3 and REM sleep, plays a crucial role in physical restoration and repair. During this time, your cells undergo repair and growth, and hormones are secreted to promote muscle and bone development.
Additionally, your body’s immune system is strengthened during deep sleep, enabling you to combat infections and illnesses. Overall, deep sleep is essential for maintaining optimal physical health.
Sequence of Sleep Stages
It’s important to understand that the four stages of sleep do not always occur in a perfect sequential order.
When you have an uninterrupted night of sleep, the stages usually progress in the following order:
- You start with NREM stage 1 sleep.
- NREM stage 1 transitions into NREM stage 2.
- NREM stage 2 is followed by NREM stage 3.
- NREM stage 2 is repeated.
- You then enter REM sleep.
After the completion of the REM sleep stage, the body typically transitions back to NREM stage 2 before the cycle begins again.
The amount of time spent in each stage may vary throughout the night as the cycle repeats itself four to five times. This pattern of cycles and stages is referred to as sleep architecture, and a sleep specialist can display this information using a hypnogram, which is a graph generated by an EEG.
Factors That Affect Your Sleep Cycle
A complete sleep cycle usually lasts for 90 to 110 minutes.
However, if you experience difficulty falling asleep or staying asleep, it can affect your sleep cycle. When your sleep is interrupted, it means your sleep is not continuous throughout the night.
This can disrupt your sleep cycle and cause an in-progress sleep stage to be cut short, or a cycle may repeat before finishing.
There are various factors that can disturb your sleep cycles, and these disruptions can occur either occasionally or on a chronic basis, depending on the underlying cause.
Here are some factors that may lead to interrupted sleep, affecting sleep stages:
- Older age: Lighter sleep and easier awakening
- Nocturia: Frequent need to urinate during the night
- Sleep disorders, such as obstructive sleep apnea (breathing stopping and starting during sleep) and restless leg syndrome (intense need to move the legs)
- Pain: Difficulty falling or staying asleep due to acute or chronic pain conditions, like fibromyalgia
- Mood disorders, such as depression and bipolar disorder
- Other health conditions, including Alzheimer’s disease, Parkinson’s disease, obesity, heart disease, and asthma
- Lifestyle habits: Lack of exercise, smoking, excessive caffeine consumption, and excessive alcohol consumption.
What Happens When Sleep Stages Are Altered
Insufficient time spent in each sleep stage or disrupted cycling through the stages of sleep can impact a person in different ways, which may lead to short-term or long-term consequences.
Disrupted sleep cycles can cause a range of issues, including:
- Difficulties with learning and concentration
- Reduced creativity
- Impaired decision-making abilities
- Problems with problem-solving
- Impaired memory recall
- Difficulty controlling emotions and behaviors
Individuals with a disrupted sleep cycle have an increased risk of developing the following health problems:
- Chronic pain
- Inflammation
- High blood pressure
- Heart disease
- Overweight/obesity
- Diabetes
- Reduced quality of life.
Tips For a Healthier Sleep Cycle
The Centers for Disease Control and Prevention has reported that 33% of adults in the United States do not get enough sleep. To improve the quality and quantity of sleep, there are certain things that everyone can try.
According to the Centers for Disease Control and Prevention, 1 in 3 adults in the US reports not getting enough sleep.15 There are things everyone can try to help improve the quality and quantity of sleep.
- Reduce the use of electronic devices before bedtime.
- Spend some time outside in natural sunlight for at least 30 minutes a day.
- Maintain a consistent sleep schedule by going to bed and waking up at the same time every day.
- Engage in regular exercise.
- Avoid eating a heavy meal before bedtime.
- Limit or avoid alcohol consumption.
- Keep the bedroom environment cool and dark.
- Ensure adequate sleep duration. Longer sleep duration increases the amount of REM sleep.
By practicing good sleep hygiene, it is often possible to improve the quantity and quality of sleep. However, if you have tried the above tips for at least a week and still do not get sufficient sleep, it is advisable to consult a healthcare professional.
They can assess if you require additional assistance, such as medication or a sleep apnea device.
Recap
As you go through the four stages of the sleep cycle, your body undergoes various biological processes that affect your temperature, breathing, cells, and muscles.
At the same time, your brain works on forming, organizing, and storing memories. Although the sleep cycle typically follows a specific pattern, it can be disrupted by various factors such as habits, health conditions, and aging.
If you don’t get enough sleep or don’t cycle through the four stages properly, it can lead to long-term physical and mental health problems.
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