The Stages of Sleep

September 01, 2021

The Stages of Sleep

The Stages of Sleep 

As you sleep your brain cycles through four stages of sleep. Each stage has a unique role in maintaining both your body and brain's overall health and development. The entire sleep cycle repeats itself several times a night with every successive REM stage increasing not only in depth of sleep but duration as well. In this article we go over the stages of sleep, what happens within your body as each stage occurs, and what can inhibit your ability to move through these stages. 

What Are The Stages of Sleep? 

There are four different stages of sleep. Stages 1 through 3 are known as non-rapid eye movement (NREM) sleep, also referred to as quiet sleep. The fourth stage of sleep is rapid eye movement (REM) sleep. The sleeping stages used to be divided into five different stages, however, this was changed by the American Academy of Sleep Medicine (AASM) in 2007. 

Entering The Stages of Sleep 

Using a non-invasive test called an electroencephalogram (EEG) that records brain activity, doctors and scientists are able to witness how the brain engages during various mental activities as a person falls asleep. During stage 1 and during the beginning of stage 2, you are still relatively alert and can be woken up easily. At this time, the brain produces beta waves which are small and fast brainwaves that mean the brain is active and still engaged. As the sleeping stages progress and the brain begins to wind down it lights up with alpha waves. 

Stage 1 of Sleep 

As we briefly mentioned above, the first stage of the sleep cycle is actually just a transition between being awake (wakefulness) and sleep. During this period it is easy to be woken up and oftentimes, if you are to wake someone up during this stage they may claim that they've been up the whole time and were never really asleep. During stage 1: 

  • Your brain slows down
  • Your body relaxes, although your muscles may twitch
  • Your heartbeat and breathing slows in unison

This is only a "short-lived" sleep period that last for around 10 minutes before you move on to the next stage of sleep. 

    NREM Stage 2

    Studies suggest that people spend nearly 50% of their total time asleep during NREM stage 2. This stage lasts around 25 minutes during the beginning of the cycle and lengthens with each successive cycle. This stage represents much deeper sleep then stage 1 as your heart rate and body temperature begin to drop. During this stage of sleep: 

    • Your body temperature and heart rate drop
    • Your eye movements come to a halt
    • Your breathing becomes more relaxed
    • Your muscles begin to relax

    The brain also starts to produce sleep spindles which are intense bursts of rapid, rhythmic brain wave activity thought to be associated wth memory consolidation. This is when your brain gathers, processes, and filters new memories that you acquired the previous day. As all of this memory consolidation is occurring, your body slows down even more in preparation for the next stage: NREM stage 3 sleep.  

    NREM Stage 3

    This is considered the deepest stage of sleep where delta waves, also known as slow brain waves, begin to emerge. If someone is awoken during this stage they will experience a period of mental fogginess. In fact, cognitive testing has shown that individuals that are inadvertently woken up during this stage tend to have their mental performance moderately impaired for at least 30 minutes to hour after being woken up. Stage 3 is when the body repairs and regrows its tissues, builds bone and muscles, and also strengthens the immune system. It is vital that you get enough NREM stage 3 sleep each night in order to feel refreshed and ready to take on the day.

    During NREM stage 3: 

    • Your body and muscles are completely relaxed
    • Your blood pressure drops
    • You are in your deepest sleep
    • Most difficult stage to be awoken from
    • Your brain consolidates memories

    REM Sleep Stage 4

    This is often the most talked about and perhaps most well-known stage of sleep. REM sleep begins 90 minutes after falling asleep and in this stage, your body is temporarily paralyzed—a good thing considering it prevents you from acting out your dreams. During stage 4: 

    • Your body is relaxed and you are completely immobilized
    • You dream
    • Your eyes move rapidly
    • The EEG is similar to an awake individual 
    • Your breathing speeds up

    Similar to stage 3, memory consolidation also occurs during REM sleep. Unlike stage 3, however, REM sleep is when emotions and emotional memories are processed and stored.  

    What's Happening While You Sleep? 

    During both stage 3 and REM sleep (deep sleep), your cells repair and rebuild, and hormones such as human growth hormone (HGH) are secreted to promote bone and muscle growth. It is also during these stages that your immune system is strengthened helping you fight off illnesses. 

    More About Sleep Stages

    Interestingly enough, sleep does not always progress through the four stages outlined above in a perfect sequence each night. A healthy, uninterrupted night of sleep progresses like so: 

    • Sleep begins with stage 1
    • Stage 2 follows stage 1 
    • NREM stage 3 begins after stage 2
    • NREM stage 2 is repeated before REM
    • Now you are in REM sleep

    Once your REM sleep cycle is complete, you usually return to NREM stage 2, which is the longest stage of sleep, before starting the cycle all over again. It is important to make sleep a priority each night. Although the exact amount of time varies from person to person doctors and scientists recommend that you get 7 to 9 hours of sleep each night. 

    Is There Something That Can Interrupt Your Cycle? 

    There are actually a number of things that can interrupt your cycle each night and disrupt your sleep. This includes but is not limited to: 

    • Pain: Acute or chronic pain may make it difficult to fall asleep each night.
    • Sleep disorders: This includes sleep apnea (breathing that starts and stops suddenly during sleep) and restless leg syndrome often associated with low levels of iron. Naturally support better sleep quality with the help of clinically studied ingredients like soothing valerian root extract, l-theanine, and passionflower in Easy sleep, an all-natural sleep supplement. You can shop Easy Sleep here
    • Older age: As you age it becomes easier to be awoken during sleep. 
    • Nocturia: A condition in which you wake up during the night because you have to urinate. 
    • Mood disorders: Depression, anxiety, and bipolar disorder can make it difficult to fall asleep and stay asleep. You can shop anxiety and depression supplements like Thought Calmer here
    • Lifestyle choices: Poor lifestyle habits can make it very difficult to fall asleep. This includes little/no exercise, smoking, excessive caffeine and alcohol use. 
    • Blue light: Studies show that the use of blue light—light emitted from your smartphone, tv, or tablet can negatively impact your sleep/wake cycle.  

    The Stages of Sleep Summary 

    There are four different stages of sleep. There used to be five, however, this was changed by the American Academy of Sleep Medicine (AASM) in 2007. 

    As you sleep your brain cycles through these four stages. Each stage has a unique role in maintaining both your body and brain's overall health and development. The entire sleep cycle repeats itself several times a night with every successive REM stage increasing not only in depth of sleep but duration as well. 

    Frequently Asked Questions About Sleep Stages

    The Stages of Sleep Questions

    Q: What are the 5 stages of sleep?

    A: As we have discussed above, there are no longer 5 stages of sleep. Since 2007, there are only 4 stages. 

    Q: What is the most important stage of sleep?

    A: Scientists agree that deep sleep (stage 2 and 3) are the most important stages of sleep. 

    Q: What stage of sleep is hardest to awaken?

    A: It is most difficult to awaken people from slow-wave sleep; hence it is considered to be the deepest stage of sleep.

    Q: What causes lack of deep sleep?

    A: Causes of lack of deep sleep include stress and anxiety, restless leg syndrome, too much blue light before bed, lack of exercise, as well as poor lifestyle habits and choices. 

    Q: How long is a sleep cycle?

    A: A full sleep cycle takes about 90 to 110 minutes.



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