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Sleep is an important part of our lives. We spend about one-third of our time in this dream state. That shouldn’t come as a surprise considering the fact that it is as essential to us as food and water are. We can’t survive without it.
If we are deprived of sleep, our brain can’t create or maintain the pathways that let us learn and form new memories. Without sleep, our neurons can’t communicate with each other.
Even though sleep comes very naturally to us, it’s still one of the least understood functions of our brain. Scientists have only just begun to understand what happens to us while we are dreaming.
If you are like most people, then you might think that during sleep, every part of us is resting. However, the truth is that both our brain and body remain very active. And that’s the biggest mystery of sleep.
So what happens to our brain and body when we are asleep? And what are sleep mechanisms?
Several parts of our brain are involved with sleep. We have hypothalamus, which contains groups of nerve cells that control sleep. Then we also got the brain stem that communicates with the hypothalamus to control the transitions between wake and sleep. The brain stem also prevents us from moving during REM sleep.
Next is thalamus, one of the most active parts during REM sleep, which sends the sensations we experience during our dreams. The pineal gland increases the production of melatonin, helping us to fall asleep.
There is also basal forebrain that releases adenosine to support the sleep drive. Last but not least, we should mention the amygdala, the emotional part of the brain that fires up during REM sleep.
When it comes to sleep, it has only two basic types – REM (rapid eye movement) sleep and non-REM sleep. Non-REM sleep has three additional stages that occur several times during the night, in combination with REM sleep.
What’s most interesting to know is that the REM periods are longer and deeper the closer we get to the morning. Non-REM sleep stays the same throughout the night.
The first stage of non-REM sleep is falling asleep, and it lasts only several minutes. The second stage includes a period of light sleep, and the third stage is deep sleep. The third stage is needed for our body and brain to feel rested after we wake up in the morning. During all of these stages, our body is relaxed, and our heartbeat and breathing are slow.
REM sleep is when things get really interesting. Our eyes start to move rapidly from side to side, and our brain activity is almost as high as when we are awake. Breathing becomes faster and irregular, and both our blood pressure and heart rate are increased. We usually start to dream during REM sleep, and our entire body becomes paralyzed so we won’t act out our dreams.
Our sleep cycle is being controlled by two internal biological mechanisms - the circadian rhythm and homeostasis. They help regulate when we are asleep and when we are awake. One cannot work without the other, so they both are synchronized to help us be aware of what our mind and body need. They are also connected to nature’s day/night cycle.
The circadian rhythm is an approximately 24-hour cycle that consists of several different functions (metabolism, body temperature, the release of hormones, etc.) that control how our body acts, making us sleepy at night and awake in the morning. Our inner biological clock is what controls our circadian rhythm, and this is usually connected to the actual time of day.
On the other hand, homeostasis is the mechanism that keeps track of our need to sleep. It tells our body when it’s time to sleep, and it also regulates sleep intensity. That means the longer we are awake, the stronger the sleep drive will try to remind us that it is time to go to bed and get some rest.
This mechanism is also sensitive to light, so it might be more difficult to sense the signs during daylight.
As you can see, sleep is much more complex than one might think. And this is only the beginning of what we have discovered so far. Our brain hides so many mysteries and secrets that we might never be able to learn them all. But this makes things much more interesting, would you agree?