The 4 Stages of Sleep: Understand What Happens In Each Stage.


Understand What Happens In Each Stage.

An average person sleeps 8 hours out of 24 hours. So, in a typical life span of 75 years, we sleep for 25 years.

The importance of a good night’s sleep is known to all. In fact, it is as important as breathing, eating, and drinking. The role of sleep on our mental and physical health is known thanks to scientific studies and research. But, despite the fact that we devote nearly one-third of our life sleeping, very little is known about the nature of sleep. This is my first article on sleep which will be followed by many articles uncovering various scientific research in the last two decades. Believe me, it’s going to be an interesting journey.

Let me begin the journey with a very interesting and informative article on various stages of sleep and their impact on our brain and body.

There are 2 basic types of sleep with 4 sleep stages: Rapid Eye Movement (REM) and Non- Rapid Eye Movement (NREM). NREM sleep has 3 different stages known as N1, N2, and N3 stages.

Thanks to technological advancements availability of non-invasive tools like Electroencephalograph (EEG) allows scientists and sleep researchers to record brainwave frequencies during sleep and also allows them to see different functions of the brains along with other biological rhythms, including eye movement and muscle movement. Interestingly researchers observed that each stage shows distinct brain wave patterns. Thus, each stage has a unique role and function in maintaining your brain and body’s overall performance. A sleep specialist can show you this information on a graph known as the hypnogram- produced by EEG.

Let’s understand each stage in detail for better awareness.

NREM Stage 1.

The first stage of NREM sleep is called stage 1 (N1). This is the changeover stage where the transition from wakefulness to sleep onset happens. This so-called, “Dozing off” stage leads to changes in both brain and body.

As far as changes in the body are concerned:

      • Body temperature begins to drop.
      • Heartbeat slows down.
      • Eye movement slows down.
      • Breathing goes slow
      • Muscles began to relax.

The body starts to slow its rhythm. In terms of brain activity, both alpha and theta waves are associated with stage 1.

The beginning of stage 1 produces alpha waves which are low frequency (8-13 Hz) waves, but as the sleeper continues on the night journey, there is an increase in theta waves which are even lower wave frequency (4-7 Hz) than alpha. The theta waves assist in inducing deeper sleep and the movement from N1 to N2 stage.

This stage of sleep is the lightest stage. You are probably somewhere alert and aware of your surroundings and happenings. So, you can be easily woken up by noises and other disturbances and might feel that you have not slept at all. This stage lasts for about 5-10 minutes and during the entire sleep cycle, a sleeper may not spend much time in N1.

NREM Stage 2

Stage 2 of NREM sleep (N2) is a period of transition from light sleep to deep sleep. The body in this stage enters a more subdued state which is characterized by:

  • Body temperature drops further.
  • Eye movement stops.
  • Muscles relax further.
  • Breathing and heart rate drop further.

The body goes further into a state of deep relaxation. But the real action happens in the brain.

Though Theta waves dominate this stage but they are interrupted by short bursts of electrical activity called, “Sleep Spindles,” Sleep researchers and scientists believe that during sleep spindles, the brain disconnects from your senses and begins the very important process of memory consolidation (meaning it organizes memories for long term storage). Sleep spindles are important for learning and memory.

EEG also shows a typical pattern called, “K-Complexes.” What are these k-complexes? During the wake period, they respond to stimuli from the surrounding environment, but during the sleep period, the same k-complexes waveform helps you sleep undisturbed, even when there is a disturbance in the environment like light, noise, or movement. It is observed interestingly that when you whisper someone’s name during stage-2 a k- complex waveform will appear on the screen.

Though this stage lasts for 20-25 minutes, according to American Sleep Foundation and other studies, people spend approximately 50% sleep time in the N2 stage.

NREM Stage 3

As N2 sleep progresses during the cycle there is a gradual appearance of high voltage slow wave frequency activities which are the character of N3 the third and final stage of NREM sleep.

This stage is referred to as slow-wave sleep (SWS), delta sleep, or deep sleep. It is the most restorative and restful stage. This stage leads to changes in both body and brain. During this stage:

  • Heart rate and breathing slows down to the lowest.
  • Blood pressure drop further.
  • Body temperature drops further.
  • Eye movement stops.
  • Muscles are completely relaxed.

The brain activity in this period shows a pattern of delta waves. During this stage, both body and brain go in repair and recovery mode. Growth hormone secretion is at its peak in SWS sleep. In fact, in men, 70% of the Growth hormone is secreted during this stage.

Following are the important functions of Human growth hormones:

  • It maintains, builds, and repairs muscles and tissues and promotes bone growth.
  • It helps children and adolescents grow tall.
  • It reduces body fat by increasing bone density and muscle mass.
  • It also controls the body’s metabolism, a process in which cells in your body changes food into energy that the body needs to function.
  • It contributes to the regulation of body fluids, fat, and sugar metabolism and also functions of the heart.
  • It improves skin tone.
  • It leads to a rise in energy levels.

So, if you really want to grow tall and have the above benefits, then you know the secret now, get a good night’s sleep.

This stage lasts 30-40 minutes. Being deep sleep is when your brain becomes less responsive to external stimuli and triggers. Thus, it is difficult to wake up a person from this stage. Studies have shown that very loud noises even over 100 decibels are sometimes unable to wake up the sleeper. But if woken up by force, you may feel groggy and disoriented for some time.

In interesting research when subjects were woken up from N3 sleep and were asked to carry out some cognitive tests, it was observed that for at least 30 minutes or more their mental performance got impacted. A phenomenon is also called “Sleep Inertia.”

Slow-wave sleep occurs for longer periods in babies and young children, and the time spent in N3 decreases with advancing age. This is tied to SWS being produced in a brain area known as the medial prefrontal cortex. This area deteriorates over time as we age and as a result older people typically experience less SWS during a normal sleep cycle.

REM Stage

This is the place of sweet dreams. In this stage what happens is:

  • The eyelids flutter and eyes move rapidly behind the lids, hence the name REM.
  • Blood pressure and heart rate increase.
  • Breathing becomes irregular and erratic.
  • Temperature regulation is switched off.

As far as the brain is concerned its activity increases and mimics the waking state. Amazingly the graph of both N1 and REM look alike. That’s why it is a stage of intense dreams.

But the question arises, why don’t we act on our dreams. The answer to this question is amazing and will force us to thank mother nature for it. What happens is that our brain sends a signal to body muscles and disables it, thereby temporarily paralyzing arms and legs muscles thus preventing us from acting on our dreams.

Just imagine you are dreaming about bungee jumping and had it not for your brain paralyzing your muscles, you would have leaped out from your window. During dreams, your body becomes immobile like a statue. How cool! I am sure this will force you to offer gratitude to nature.

Like stage 3 this stage too plays a crucial role in brain function. It stimulates and triggers sections of the brain that are key for cognitive functions like memory and creativity. Ditto stage 3 memory consolidation also happens during this stage. Sleep researchers believe that it is REM sleep where emotions and emotional memories are processed and stored. Your brain uses this period to consolidate information into memory, which is key for learning. Hence, REM sleep is crucial for both memory and learning.

The first REM sleep period occurs approximately 90 minutes into the sleep cycle. It lasts only 10 minutes but increases with each REM cycle. As the night goes on REM stages get longer and longer, especially in the 2nd half of the night. The final cycle is assumed to last for almost 60 minutes.

Aging too affects this stage. The amount of REM sleeps you experience is highest during infancy and early childhood. Babies can spend up to 50% of their sleep in REM. It declines during adolescence and young adulthood and declines even further as you get older. Adults spend just 20-25% of their sleep in REM.

The bottom line:

If health is wealth, then along with exercise and nutrition, good sleep is one of the pillars of sound health. So do not hate yourself for spending so much time asleep. Don’t defend yourself by saying, “I am not sleeping, just resting my eye.” You cannot achieve fruitful life and good health without taking care of your sleep.

Be great in Bed!

Sweet Dreams!

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