Sleep Stages: Understanding The 4 Stages Of Sleep, Sleep Cycle

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Are you curious about your body while you are sleeping? And how can we ensure the best quality of sleep? In order to be able to answer these questions, let’s start with analyzing the human mind. Let’s find out together! You know, while sleeping, the brain is working hard to store memories, heal tissues and restore the body. To do all this, it has to go through a total of four stages of sleep that are repeated several times each night. These stages are classified as REM and Non-REM sleep.

What is the sleep cycle?

A full cycle takes around 90 to 110 minutes. The first cycle is usually shorter with deep sleep taking the lion’s share and the REM stage being shorter. As the night progresses, the deep sleep phase becomes shorter while the REM phase increases. As we approach the end of our sleep, it is mainly split between stages 1, 2 and the REM stages.

Sleep Stages: Understanding The 4 Stages Of Sleep, Sleep Cycle

It is a noted pattern that people who are awoken a few minutes after they sleep rarely remember the activities that took place a few minutes before they slept. This explains why phone conversations that take place in the middle of the night may be forgotten or why some people rarely remember turning off their alarms.

The 4 Stages of Sleep

Sleep Stages: Understanding The 4 Stages Of Sleep, Sleep Cycle

NREM Stage 1

Stage 1 is the beginning of the sleep cycle and is a relatively light stage of sleep. Stage 1 can be considered a transition period between wakefulness and sleep.

In Stage 1, the brain produces high amplitude theta waves, which are very slow brain waves. This period of sleep lasts only a brief time (around five to 10 minutes).5 If you awaken someone during this stage, they might report that they were not really asleep.

NREM Stage 2

Stage 2 is the second stage of sleep and lasts for approximately 20 minutes. During stage 2 sleep:

  • You become less aware of your surroundings.
  • Body temperature drops.
  • Breathing and heart rate become more regular.

The brain begins to produce bursts of rapid, rhythmic brain wave activity known as sleep spindles. Body temperature starts to decrease and heart rate begins to slow. According to the American Sleep Foundation, people spend approximately 50% of their total sleep in this stage.5

NREM Stage 3

During stage 3 sleep:

  • Muscles relax.
  • Blood pressure and breathing rate drop.
  • Deepest sleep occurs.

This stage was previously divided into stages 3 and 4. Deep, slow brain waves known as delta waves begin to emerge during stage 3 sleep. This stage is also sometimes referred to as delta sleep.

During this stage, people become less responsive and noises and activity in the environment may fail to generate a response. It also acts as a transitional period between light sleep and a very deep sleep.

Older studies suggested that bed-wetting was most likely to occur during this deep stage of sleep, but some more recent evidence suggests that such bed-wetting can also occur at other stages. Sleepwalking also tends to occur most often during the deep sleep of this stage.

REM Sleep

During REM sleep:

  • The brain becomes more active.
  • The body becomes relaxed and immobilized.
  • Dreams occur.
  • Eyes move rapidly.

Most dreaming occurs during the fourth stage of sleep, known as rapid eye movement (REM) sleep. REM sleep is characterized by eye movement, increased respiration rate, and increased brain activity. The American Sleep Foundation suggests that people spend approximately 20% of their total sleep in this stage.

REM sleep is also referred to as paradoxical sleep because while the brain and other body systems become more active, muscles become more relaxed. Dreaming occurs due to increased brain activity, but voluntary muscles become immobilized.

When Sleep Goes Wrong

Sleep Stages: Understanding The 4 Stages Of Sleep, Sleep Cycle

When you’re not getting enough sleep, or if your quality of sleep is poor, all of the positive things that happen in sleep—as described above—decrease. Your body is unable to repair effectively, biological processes are disturbed, and there are significant effects on brain function and cognition.

Lack of quality sleep can impact:

  • Heart health. While you sleep your heart takes a rest. It doesn’t need to pump large amounts of blood to your muscles or digestive system. Of course it continues to pump blood to your brain and all around the body, just less vigorously. Lack of sleep puts an increased strain on your heart.
  • Hormonal systems. Your hormonal or endocrine system produces chemicals essential to every cell, system and organ in your body. Lack of sleep interferes with hormone release and cellular repair, growth, blood pressure, blood sugar, and sexual health. In teenagers, lack of sleep can interfere with puberty.
  • Memory. Lack of sleep limits consolidation of memory, making it difficult to lay down long-term memories.
  • Cognitive performance. Lack of sleep will reduce focus, slow processing, and cause errors and may also contribute to poor decision-making and impulsivity.
  • Motor skills. Lack of sleep can make you more likely to make mistakes and have an accident.
  • Mood. Lack of sleep increases the risk of negativity, depression, anxiety and may worsen serious psychiatric conditions such as bipolar disorder.
  • Immune health. Lack of sleep weakens the immune system making you more prone to infection.