Sleeping people seem so peaceful. They look like they don’t have a care in the world, like their bodies are completely at rest. Underneath this placid surface, though, the body and the brain are working hard. A lot goes on when you’re asleep, even if you don’t realize it.
The process of falling asleep seems to involve two different processes in the brain. They each affect different parts of the brain but, together, these processes tell the brain when it’s time to sleep.
The first of these is the circadian rhythm. This is the body’s internal clock and the method by which the body regulates many functions, including sleep. It also plays a part in how we know when to eat, in the ways our energy rises and falls during the day, and the way we almost always have some idea of what time it is.
Certain parts of the brain are regulated by this process. Under the rule of the circadian rhythm, it doesn’t matter how long you’ve gone since you last slept. Instead, it matters what time it is in your body.
This is why jet lag can be so disruptive, because at least part of your brain wants to fall asleep when it’s bedtime, whether you’ve been up for 16 hours or 6.
The second process that helps you sleep is called your homeostatic sleep drive. This is the process that tells you to sleep after you’ve been awake for a certain amount of time. Scientists liken this process to an hourglass. For every hour you’re awake, sand drops through the glass. The more sand that’s gone through, the more you feel the need to sleep.
When your circadian rhythm and your sleep drive are telling you it’s time to rest, the neurotransmitters in your brain change. This causes your neurons to begin to fire differently, which eventually leads to sleep.
The Stages of Sleep
Once you’ve fallen asleep, your body goes through 4 stages of sleep. It cycles through these roughly once every 90 minutes, and most people get through 4 or 5 cycles every night. The first three stages make up non-REM sleep. REM sleep and non-REM sleep have very different brain wave patterns and activity patterns in your neurons.
Stage 1 Sleep
In Stage 1 sleep, you’re actually transitioning from being awake to being asleep. This stage only lasts for a few minutes. During it, your heartbeat begins to slow, as do your respiration rate and your eye movement. Your body also relaxes, though your muscles may twitch occasionally. Your brain shifts from its waking patterns to sleeping ones.
Stage 2 Sleep
This is an extension of Stage 1 sleep. Your heart rate and respiration rate slow even further, and your body temperature begins to drop. Your eyes stop moving altogether and your brain waves slow even more. There may be sudden bursts of electrical activity in the brain, but it is definitely moving toward deeper sleep. You spend most of your night in Stage 2 sleep.
Stage 3 Sleep
This is the deepest stage of sleep that you experience. Your heart rate and respiration rate are lower here than at any other time during the night, and your muscles are completely relaxed. This is the sleep that you need to have to feel well-rested in the morning, and it occurs in longer periods during the first half of the night.
In REM sleep, your brain activity picks up again, even rivaling what it is when you’re wide awake. Your eyes twitch, though your muscles are paralyzed. You breathe quickly and the pattern may even become irregular, and your heart rate rises to nearly where it is when you’re awake. Most dreaming takes place in REM sleep. Periods of REM sleep increase during the second half of the night.
Why We Need Sleep
All of this is interesting, but what’s the point? Is there a reason we sleep, or did our bodies develop these weird patterns for no discernable purpose? Fortunately, sleep seems to serve several purposes.
Clearing Out Toxins
The brain and the body build up certain toxins during the day. These are generally byproducts of normal functioning and they won’t hurt you as long as they get cleaned out. This cleaning process happens while you’re asleep. Certain neurological diseases seem to correlate with a lack of sleep, and scientists believe that they may be a product of brains that don’t have time to clean themselves out properly.
Your body repairs its tissues while you’re asleep. Some of these are things you might never notice, like micro tears in your muscles or damage on a cellular level. Major healing occurs during sleep, too. This is part of the reason why we feel extra tired when we’re sick or coming out of surgery. Without sleep, our self-repair becomes much less efficient.
Since both the breathing rate and the heart rate are lower during sleep than at other times of day, both the lungs and the heart get a bit of a rest. This not only saves you the energy of powering these organs at full blast 24/7, but it also means that they last longer and can repair themselves better. Since most of us want our heart and lungs to last a long time, getting plenty of sleep seems like a good idea!
Sleep isn’t only something we want to do, it’s something our bodies need us to do. Most of us, sadly, aren’t sleeping enough and our bodies are paying the price. It’s worth the effort to figure out how to get even a little more sleep, as the hours add up over time.