A Rough Guide to 'Sleep' That You Might Be Too Embarrassed to Ask About
Hello!
This time, I'm going to explain what happens while humans are asleep.
I'll be covering this.
I'll be introducing the process roughly in order from just before you fall asleep until you wake up, so it might be a little long, but please bear with me.
1. Just before sleep - Entering relax mode
Preparation for body temperature to drop begins
As long as you are living a healthy lifestyle, the human biological clock moves in line with the world clock—the natural cycle of waking up when the sun rises and falling asleep when the sun sets. So, when night comes, your body says, 'It's time to sleep.' Then, it starts to release heat from your hands and feet to lower your body temperature. When your core body temperature, which is deep inside your body, drops, you start to feel sleepy.
Hormone secretion starts
Humans have a hormone called 'melatonin' that makes us feel sleepy, and when this is secreted, the whole body enters a relaxation mode. Some people don't feel it due to a disrupted lifestyle, but for now, you can just think 'sleepiness = melatonin has been released'!
2. Beginning of sleep - Light non-REM sleep
The brain and body begin preparing to rest
If you are living a healthy life, humans reach this stage in about 10 minutes. The brain, which was active, gradually slows down, and your heart rate and breathing become calmer. At the same time, the muscles throughout your body relax and go limp.
It might look like just a relaxation time, but if this stage doesn't go smoothly, the subsequent stages will be a mess!
3. Maintenance time - Deep non-REM sleep
Treating wounds
Growth hormones are released, and damaged cells and muscles in the body are repaired. This system is why scabs form on wounds and muscle pain heals.
Reviewing the immune system
Various immune components like white blood cells start working at full capacity, and preparations to protect the body begin. It doesn't just cure colds and illnesses; it also helps make you less prone to feeling unwell.
Brain deep cleaning
Waste—trash—also accumulates in the brain. If too much of it builds up, it can lead to dangerous diseases. This time is also for thoroughly washing away and cleaning up that brain trash. Because of this deep cleaning, you can feel refreshed when you wake up in the morning!
4. Time for dreaming - REM sleep
Organizing memories and taking out the trash
During REM sleep, when the brain is active and organizing memories, it compiles the information and experiences gained during the day so that they are 'easy for you to use,' and etches them deeply so you don't repeat the same mistakes. Conversely, it can also erase unnecessary memories. Furthermore, by processing emotions, it allows you to discard unpleasant memories. The reason you can feel refreshed after sleeping even when something bad has happened is because this 'trash disposal' function is working properly.
Dreaming
The actual cause of why people dream is still not clearly understood. However, a professor in Chicago conducted experiments on REM sleep, and since 80-90% of subjects awakened during REM sleep reported that they 'were dreaming,' it began to be said that we dream during REM sleep—in other words, that the memory organization occurring during REM sleep appears in our dreams.
Therefore, it is more accurate to say that 'many people dream at this stage.' It seems that some people can even dream during non-REM sleep. While dreams during REM sleep are 'dramatic and emotionally rich,' dreams during non-REM sleep are often 'realistic and plain.' It's mysterious, isn't it?
5. Alternating between REM and non-REM sleep
Sleep is structured by alternating between REM and non-REM cycles approximately every 90 to 120 minutes. At first, there is more non-REM sleep, and as it gets closer to morning, the duration of REM sleep increases. This is the reason why it is harder to wake up at night and easier to wake up in the morning.
6. Preparing to wake up
Cortisol's 'clock-in' time
Cortisol, also known as the stress hormone, is actually a 'wake-up hormone' necessary for waking up feeling refreshed in the morning. During sleep, melatonin suppresses the secretion of cortisol, but the morning is the time for them to pass the baton.
Body temperature rises
Since the body operates according to the natural rhythm explained earlier, as morning approaches, the body tries to 'wake up' and raises its temperature. If a drop in core body temperature makes you sleepy, then a rise in it will wake you up. By the way, what is necessary for falling asleep or waking up is not just the core body temperature, but the difference between the 'skin surface temperature' and the core body temperature. The wider the gap, the more awake you become, which is why washing your hands and face in the morning has a good effect on waking up. Did you know that?
7. Waking up!
The brain and body are fully connected! Organized memories and emotions are settled throughout the body, and you start a day feeling refreshed in both body and mind.
Summary
This is a rough summary of human sleep.
In this way, humans prepare for tomorrow by repeating repair time, cleaning time, and organization time. For now, it's fine if you've just grasped a rough idea of what is happening from this article!
That's all for this time.