How Sleep Works: A Complete Guide

How Sleep Works: A Complete Guide

For between six and nine hours per day, most of us are asleep. Anyone good at maths can figure out that this means we spend roughly one quarter to one-third of our lives asleep. But how many of us stop to think about what sleep really is and how sleep works?

We know it’s important; dragging ourselves out of bed and into work after a lousy night’s sleep is one of the worst things ever. But why? What is the difference between a good and a bad night’s sleep? Why do we sometimes wake up feeling refreshed and ready to conquer the world, yet other day’s we wake up feeling like someone just punched us in the face?

Today, we’re going to address these questions and more, helping you gain a better understanding of how sleep works and what needs to happen for it to be truly restful and beneficial.

What is Sleep?

When we look at a sleeping person, it’s easy to think of them as “inactive.” After all, they’re just lying there, moving only slightly and breathing easily. Because of this, for many years, scientists considered sleep to be a period when the brain and the body “shut down” to restore itself. And while the primary purpose of sleep is restoration and regeneration, describing the time we spend sleeping as “inactive” would be a gross mischaracterization of this all-important bodily function.

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Sleep is first and foremost a neurological process. It’s controlled largely by the hypothalamus, a peanut-sized piece of the brain containing the nerve cells that determine whether we are awake or asleep. These cells are affected by the amount of light outside, and they dictate the creation and distribution of melatonin, a naturally-occurring hormone that helps you fall and stay asleep.
During this process, neurons inside the brain shut off certain brain functions that keep us awake, largely the production of serotonin and norepinephrine, two types of neurotransmitters that regulate wakefulness. All of these processes combine to help create the state of activity we know as sleep.

Some of the secondary effects of this transition are that our heart and breathing rates decrease, and our body temperature begins to drop. And, of course, we close our eyes and drift off into the world of dreamland, which may seem like a quiet, peaceful place, but that is actually a raging party of neurological activity that’s necessary for our continued survival.

What is the Circadian Rhythm

Before going too much further, it’s important to discuss the circadian rhythm. This 24-hour pattern helps to determine when you are going to sleep and when you are going to be awake. As mentioned earlier, the amount of light in your environment affects your body’s propensity to sleep. This makes sense; how much harder is it to fall asleep at 5 pm when the sun is still out? And how much harder is it to wake up at 6 am in the winter when it’s still dark outside?

Furthermore, levels of melatonin are closely linked to the circadian rhythm. Using the light outside as well as other factors, the body begins to develop a routine for when it’s time to sleep. It will begin sending melatonin out into your system at regular intervals, and this shuts down certain processes and gets the body ready for sleep.

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This is why so many sleep experts recommend avoiding screens before bed and sleeping with the TV. This excess light can cause your body to be fooled into thinking it’s daytime, throwing off your circadian rhythm and preventing the release of sleep hormones, which can keep you up or prevent you from falling into a deep, restorative sleep.

What is the Circadian Rhythm

Why Do We Sleep?

So now that we know a little bit more about what sleep is, you may be wondering why we need it. Here are three of the main functions sleep serves in our lives:


One of the primary purposes of sleep is to give your body the chance to rejuvenate itself from the wear and tear of daily life. Being awake is hard work, and the body gets tired. But if it tried to rebuild while we were still awake, then it would make it much more difficult for us to function while we are awake. So instead, we sleep so that the body’s cells can have the chance to regenerate. Our body temperature, heart rate, and breathing also all drop, helping the body conserve energy and get ready for the next day.

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The effects of this process can be easily felt. Think about if you’ve had a long day of walking, or if you pushed yourself too hard at the gym. You may fall into bed aching, but by morning you feel much better. This is because while you slept the body worked to repair any damage done by the strenuous activities you put it through. It’s for this reason sleep is so important to any exercise routine. Without it, the body would eventually break.

Cleaning House

One of the other functions of sleep, and this is one researchers are still wrapping their heads around, is that it helps to “clean” your brain. To envision this process, it’s helpful to think of your brain as a computer. During the day, it takes in a lot of information and processes it. Some of that information is virtually useless, whereas other stuff is critical. However, throughout the day, the brain, because it’s working so hard, doesn’t have time to properly sort this information and store it according to how important it is. It ends up just tossing this information wherever it can find room. But this strategy is not sustainable, which is why sleep is so important.

When you’re sleeping, the brain essentially goes through and cleans itself. It consolidates memories and stores them in the brain, or doesn’t (how many of us can remember what we had for breakfast yesterday?), which helps make room for the information that will come the next day. The brain also does other things to “clean” itself, but everything has the same purpose: optimize brain function for the next day.

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This is why a good night’s sleep is so closely linked to performance in school. People who manage to rest their brain and “clean” it out are going to be able to concentrate better and retain more information than those who did not have this opportunity to reset. Further research has built upon this notion to suggest that sleep deprivation can speed up the development of Alzheimer’s disease.

Immune Boost

How many of us have gone to the doctor while sick and received a prescription for “rest and liquids.” At the time, this can be frustrating, as we have a natural inclination to think that medicine works better. But there is a good reason for offering this prescription.
While sleeping, the body produces particular proteins known as cytokines, which are essential in helping you fight off infection. Sleeping more when sick allows your body to produce more of these proteins, giving you a better chance of overcoming your illness. And your body knows this, which is why we often feel so tired when we get sick. Our body is begging us to go to sleep so that it can produce more of what it needs to get better.

The Different Sleep Cycles

Not all sleep is the same. From the moment we close our eyes, to the moment we wake, we go through the sleep cycle, which is divided into two categories: rapid eye movement (REM) and non-REM, which has three distinct stages. Here’s a more detailed description of each:

Stage 1 Non-REM: This is the period of time right after you decide to go to sleep. It’s best known as a transitional phase, and it only lasts a few minutes. It’s during this stage that your eye movements slow, your muscles relax and your heartbeat and breathing drop. The brain has signaled to the body that it’s time to sleep, and this kickstarts the biological changes needed for your body to fall asleep.

Stage 2 Non-REM: This is the first stage of what is known as “deep sleep.” Everything slows down and relaxes even further, but your eye movements also stop. Brainwave activities slow, but there are also brief surges in activity. This is the stage in which you spend the most time during any given sleep cycle.

Stage 3 Non-REM: Have you ever fallen asleep only to wake up feeling the same if not more tired? If this has happened, then there’s a chance you never made it to the stage 3 non-REM part of the sleep cycle. But this is also a state the body reaches in the beginning part of the night, so if you can get a prolonged period to rest, then chances are you’ll get there. Breathing, heart rate, and muscle activity are at their lowest levels, and the body is in full regenerative mode at this point.

REM Sleep: It typically takes about 90 minutes for a person to enter into REM sleep. REM is named this because during this stage your eyes move rapidly from side to side behind your closed eyelids. Heart rates and breathing increase, as does brain wave activity, meaning REM sleep more closely resembles wakefulness.

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It’s during this stage that you begin to dream, and your muscles become paralyzed to prevent you from acting them out. REM sleep does not last long, and it’s common to go in and out of REM sleep throughout the night, but it’s believed that for memory consolidation (described above as “cleaning house”) to occur, your body needs a combination of REM and non-REM sleep.

Factors Affecting a Good Night’s Sleep

As you can see, sleep is a delicate process the body needs to go through to stay healthy and functional. However, a good night’s sleep is not something we all enjoy equally. Here are some things to keep in mind to help you make the most of this all-important rest time:

  • Get regular exercise (at least 20-30 minutes a day), but make sure not to do it more than a few hours before bed
  • Avoid caffeine and nicotine in the hours leading up to bed
  • Alcohol, although it gives the illusion of making us sleepy, actually causes you to wake up more throughout the night and sleep worse.
  • Avoid bright lights and sounds before bed. Turn off the TV, don’t look at your phone, and consider doing more relaxing activities, such as reading or taking a warm bath, right before bed, as all of these can help prepare your body for sleep.

If you continue to struggle falling or staying asleep, consult a doctor, as there may be a hormone imbalance preventing you from achieving a restful state.

Overall, sleep is a critical biological process the body needs in order to achieve peak performance. Understanding what sleep is, why it’s important and how to do it are all critical first steps in improving sleep levels and your overall health and well-being.

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