What Happens When We Sleep?

By Prathamesh Kapse | 7th May, 2023

Discover the fascinating world of sleep with our comprehensive guide. From the different stages of sleep to the brainwaves that govern them, learn everything you need to know about why sleep is crucial for our overall health and well-being. Dive deep into the science behind sleep and discover the incredible benefits it provides.

Welcome, to the first article of The Sleep Month. This is the first of four articles exclusively about sleep that I am writing for the month of May. Tune in every week to gain a deeper understanding of sleep and get familiar with this article, familiarize yourself with what happens when you sleep and when you avoid sleep. Enjoy!

What Exactly Is Sleep?

Sleep has always been an integral part of our lives. Whenever we’ve had a long day at work, a long day at school, or just a stressful day overall, the first thing we turn to is sleep. Sleep is undoubtedly the best refresher. I mean, it has to be. Otherwise, it wouldn't be such an important part of our lives. Sleep is just as important as regular exercise and a healthy diet. But why is it so? Most of the reasons why sleep is important are unaware of. It’s because we don’t see or feel these things happening. It goes on in our brains. Some of these things are recalling what happened throughout the day, storing important stuff in long-term memory, discarding useless information, building short-term memory, and also dreaming. 

What Happens When We Sleep?

The brain is an electrochemical organ. A fully functional brain can produce up to 10 watts of power. There are 5 types of brainwaves. Delta, Theta, Alpha, Beta, and Gamma (arranged in the increasing order of their frequencies). The brain generates oscillating electrical voltages measuring just a few millionths of a volt. These waves are active during different activities. We can say they have different functions. Delta waves are active during dreamless, pitch-black periods of sleep. Theta waves are active during light sleep or when you are relaxing. Alpha waves are active when we are relaxed or in an idle state. Beta waves are active when we are in our most conscious states. While Gamma waves are associated with learning, problem-solving, and information processing. 

Why are we reading this information? 

When we sleep, brainwaves are active. The sleep cycles are caused by these brainwaves. Generally, when we are awake and working, the brain waves are of higher frequencies and faster. But, when we are drowsy, these waves become slower and their frequency decreases. The stages of sleep are determined by the activity of these brain waves. Let’s dive a bit deeper into the sleep cycles.

Sleep cycles. 

There are two phases of sleep, (1) Rapid Eye Movement (REM), and (2) Non Rapid Eye Movement (NREM). The NREM consists of three sub-stages N1, N2, and N3. Each phase and stage includes variations in muscle tones, brainwave patterns, and eye movements. The body cycles through these stages 4-9 times a night taking an average of 90 minutes for each cycle. The 5 stages of sleep are Wake, N1, N2, N3, and REM. N1, N2, and N3 are stages of light, slightly deeper, and deep sleep. 75% of our sleep comes from the NREM stage. Let’s have a look at the stages in a little bit more detail. 

1. Wake/Alert

As clearly as the name suggests, this is the stage where we are most likely to wake up or the stage where we are aware of our surroundings mildly. Remember the brain waves we talked about? Yeah. Beta waves dominate when we are awake and about to sleep or we just got up from sleep. While Alpha waves dominate when we are drowsy and our eyes are closed. 

2. N1 (Stage 1)

As you sleep, the alpha waves start getting replaced. Their frequency starts decreasing. Eventually, when 50% of the Alpha waves are replaced by Theta waves, we enter stage 1 i.e. light sleep. The waves in this stage are not exactly theta waves, but they have low amplitudes and mixed frequencies, the stage making up for about 5% of your sleep. (Okay, I’ll be a bit less scientific and try to make more sense.) This stage lasts for a few minutes.

3. N2 (Stage 2)

This stage is where you are asleep a little bit deeper than the previous stage. It makes up for 45% of your sleep. Your heart rate and body temperature drop. There is almost no eye movement and the brain produces sleep spindles. The stage lasts for about 25 minutes.

4. N3 (Stage 3)

This stage is also known as Slow Wave Sleep (SWS). It’s the one where we have the deepest sleep. The heart rate and breathing are at their lowest (low does not mean sad. I repeat, low does not mean sad.). There are no eye movements, the body is fully relaxed and the brain is working on tissue/cell regeneration, strengthening the immune system. Delta brain waves are present at this stage.

5. REM (Rapid Eye Movement)

All the previous stages were belonging to the first phase of sleep, except Wake/Alert. This stage consists of dreams. Eye movement becomes rapid, and breathing and heart rate increase. Surprisingly, the limb muscles become temporarily paralyzed. So, overall brain activity is increased. This is not considered to be a restful sleep stage. The stage typically starts 90 minutes after you sleep with each REM cycle getting longer throughout the night. The first period typically lasts about 10 minutes with the last one lasting for about an hour. That’s why you get more vivid and longer dreams at the end of your sleep. Not to mention nightmares. 

These are the stages of sleep, in layman’s terms (I tried my best). Even though it may not look like it, sleep is confusing. There is very less understanding of sleep. It’s complex. Obviously, it’s a bizarre thing that the most complex thing in the universe does, it has to be complicated. This was all about the sleep cycles and how we sleep. Not having enough sleep or sleeping untimely can have various adverse effects on the human mind. I will discuss those in next week’s article.  

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