How Does Sleep Work?
Sleep seems like it should be simple. You close your eyes, you sleep until you’re not tired anymore, then you get up and continue on your way, repeating the cycle as necessary. If this is how you think about sleep, it may be interesting to hear that sleep is actually a complex and fascinating process that is essential to your well-being.
Why Do We Need to Sleep?
Sleep is absolutely necessary. I don’t think anyone who has ever pulled an all-nighter would tell you differently. But what actually happens when you’re asleep?
- The body repairs itself. As you go throughout the day, damage is done inside your body. Most of this involves cellular damage so small that you would never know it happened. This damage can involve cell replication mistakes, cells that stop functioning well, or cells damaged in things like microscopic muscle tears. All of this gets repaired at night when you’re asleep. Without sleep, the body would break down much faster.
- The body removes toxins. The body performs complex chemical reactions all the time. Some of these produce substances that, if permitted to build up, can be toxic to a human being. While you’re asleep, your body works on breaking these down or eliminating them in other ways. When these are allowed to build up, it becomes more likely that a person will develop certain neurological disorders.
- The body conserves itself. Many organs function significantly slower during sleep than they do during wakefulness. This includes both the heart and the lungs. When these organs aren’t working as hard, they get a chance to rest. This rejuvenates them and makes them more likely to last longer. I think we’re all fans of that!
- You maintain the ability to feel like yourself. A lack of sleep is associated with all sorts of psychiatric conditions, including depression and anxiety. While researchers don’t know the exact mechanisms by which sleep helps safeguard you from these conditions, it’s safe to say that the body and brain are maintaining themselves as-is when you sleep.
How We Fall Asleep
Ok, so we need sleep…but how does that happen? What goes on in the body to A) indicate that it’s time to fall asleep, and B) facilitate the transition from wakefulness to sleep?
Time for Bed
We know when it’s time for bed in one (or both!) of two ways. Our sleep drive keeps track of how long we’ve been awake and causes us to feel sleepy when we’ve avoided sleep for too long.
This drive has been likened to an hourglass. As we are awake, sand falls through the glass. When too much has fallen, we feel sleepy. If we still resist rest, we feel sleepier and sleepier as more sand falls.
The other way we know when to sleep has to do with our circadian rhythms. This is like an internal clock that tells the body when to do all sorts of things. It helps regulate eating and energy levels, in addition to sleep.
Each of these drives regulates different parts of the brain. They work best when they’re working together – when the time to sleep on the internal clock coincides with the time at which we’ve been awake long enough. However, the circadian rhythm can trump the sleep drive. This is what happens in jet lag. We find ourselves sleepy when the internal clock says it’s bedtime, even when we just woke up a few hours ago.
These drives help regulate the levels of various neurotransmitters in the body. While researchers are not exactly sure how neurotransmitters contribute to sleep, they do know that the balance and concentration of several of these brain chemicals change based on whether we are awake or asleep.
Adenosine is one of the most important neurotransmitters for sleep. It builds up in the body as we are awake. Once we are asleep, it begins to break down. Somehow, it seems to help regulate our sleeping and waking cycles.
What Happens While We’re Asleep
Once your drives and neurotransmitters have done their job, what next? The body accomplishes all it needs to accomplish when you’re asleep by going through 4 stages of sleep. The first three of these are non-REM sleep. Each stage has different brain wave and neurotransmitter patterns. We cycle through these stages several times each night. As the night goes on, deep sleep lessens and REM sleep is longer, though researchers are not sure why.
In this stage of sleep, the body begins the transition from wakefulness to sleep. It only lasts a few minutes. In those minutes, though, the heart rate and breathing rates slow, eye movement slows, and the muscles begin to relax. The body may still twitch, though, which can cause you to wake right up again.
This is a slightly deeper sleep than Stage 1. The body continues to relax, with the heart and breathing rates going even lower. The eyes usually stop moving altogether and muscle movements become smaller and less drastic. This is where you spend the majority of the night.
This stage of sleep is commonly referred to as “deep sleep,” and is what you need to get in order to feel rested when you wake up. In this stage, heart and breathing rates hit their lowest for the night, the eyes don’t move at all, and the body is still.
In REM sleep, it’s almost as if the body is awake, except that it’s not. Heart and breathing rates go up and the eyes begin moving again. This is when most dreaming takes place. Fortunately, the muscles are paralyzed so dreamers can’t act out their dreams.
Sleep is interesting and is a popular topic for research. As we learn more about how and when and why we sleep, we should also learn more about how to fall asleep, stay asleep, and get the most out of the hours we spend asleep.