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