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How Sleep Works: Understanding the Science of Sleep

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Update: November 15, 2022
5 min read
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Proper sleep plays a vital role in enhancing an individual’s physical and mental health. Not getting enough sleep makes you feel less energetic, causes mood swings, and even impacts the proper functioning of your brain. 

The limited information about how sleep works can profoundly influence the perception of people about this vital body function. So, this article offers information that can help people better understand the science of sleep and its impact on the body and mind.

What Happens When You Sleep?

While much still needs to be understood about the intricacies of how sleep works, researchers have established a connection between sleep and various aspects of all human body systems. They have also been able to better understand how sleep impacts the brain and the body and individuals’ physical, mental, and emotional well-being.

Most people are surprised by the fact that the body and the brain start undergoing notable changes within just a minute after they fall asleep. The body’s energy usage reduces considerably during sleep due to a decrease in body temperature. This is because the heart and respiration rates slow down, and brain activity is also reduced during sleep. 

Stages Of Sleep

As people sleep through the night, they pass through four distinct physiological stages called sleep cycles. Each cycle plays an essential role in keeping the brain and body healthy. These four stages of sleep are explained in brief as follows.

Stage 1 (NREM)

In this stage, people have just dozed off and can be easily awoken as they drift in and out of sleep. The eye movement during this stage is relatively slow, and the muscles begin to relax gradually. This stage is also called the N1 stage and lasts between 1 and 5 minutes. 

Stage 2 (NREM)

The second stage of the sleep cycle is characterized by the further slowing down of the body and brain activity which is indicated by the eye movement stopping completely. This stage of sleep lasts from 10 to 60 minutes and is referred to as N2.

Stage 3 (NREM)

In the third stage of the sleep cycle, the brain waves have the slowest sleep, and the muscles are completely relaxed. As a result, people experience the deepest sleep in this stage, which helps the body recuperate and improves memory and thinking power. The stage is known as the N3 or Deep Sleep stage and lasts anywhere between 20 to 40 minutes.

Stage 4 (REM)

During the REM sleep cycle, the body experiences a sort of temporary paralysis that does not affect the eyes and breathing. The stage is characterized by increased heart rate and blood pressure and causes penile erections in males. The stage lasts 10 to 60 seconds and occurs mainly during the night’s second half. 

Sleep And The Brain

The hypothalamus plays an important role in establishing a connection between sleep and the brain. It regulates the human body’s circadian rhythm, responsible for syncing the body with the day and night cycles. In addition, the hypothalamus connects the nervous system to the endocrine system, which controls the various chemicals and hormones involved in the sleep-wake cycle.

When people sleep, the brain rests and reorganizes itself through the process known as brain plasticity, as the sleepers experience different stages of sleep and the countless neurons in the brain change. This, in turn, impacts the brain’s functioning, primarily the ability of an individual to learn and memorize.

Sleep And The Body

The different body parts contribute in various ways to make it easier for people to enjoy a healthy and relaxing sleep. Sleeping helps the body to conserve energy and also helps to heal the body. When people sleep, the body releases growth hormones to repair and restore muscles faster.

The connection between sleep and the body is quite deep-rooted. Lack of sleep can negatively impact the smooth functioning of the body and lead to a wide range of health issues.

Chemicals And Hormones That Regulate Sleep

The chemicals and hormones produced by the body deeply impact how sleep works. The hormones help regulate individuals’ sleep-wake state by sending signals to the brain. These signals are sent through nerve-signalling chemicals called neurotransmitters, which act on specific groups of neurons in the brain to control when people sleep and when they are awake.

Melatonin is the hormone responsible for promoting sleep and is released by the body naturally as natural light reduces. Other hormones that impact the sleep-wake cycle include adrenaline, cortisol, and norepinephrine. Not getting enough sleep can hamper the effective secretion of hormones which can, in turn, affect the metabolism and other bodily functions.

Circadian Rhythm and Sleep-wake Homeostasis

The circadian rhythm is the body’s internal clock synchronized with the sun’s rising and setting. The circadian rhythm is established within the first few months after birth and controls vital body patterns such as appetite and digestion, blood pressure, body temperature, and secretion of hormones. A healthy circadian rhythm is based on a consistent pattern that makes people feel alert and active during the day and tired and sleepy after the sun sets.

Apart from the circadian rhythm, homeostasis is another biological process impacting the sleep-wake cycle. It is a term used to define the internal mechanisms of the body that make it possible for people to adapt to changing conditions to ensure their survival. The sleep-wake homeostasis guides the body about the best times to sleep and stay awake. 

Properly understanding of the circadian rhythm and sleep-wake homeostasis can help people better manage the external factors impacting them. In addition, they can use the information to develop healthy sleeping habits and maintain a proper sleep cycle to wake up refreshed and relaxed. 

Why Is Sleep Important?

Over the past several years, people have become increasingly aware of the importance of sleep in maintaining a healthy and fit life. Research has shown that sleep impacts the daily functioning and mental and physical well-being of individuals in several ways. Getting enough sleep is important to maintain healthy brain function, stay active and energetic, and ensure proper growth and development.

Even with the limited research on how sleep works, sleeping for about seven to eight hours each night is highly recommended for adults. However, the environment and lifestyle choices can impact the duration of sleep people get. In many cases, people may also not get enough sleep due to various health issues or sleep disorders. Moreover, cultural aspects may also impact the sleep structure of individuals and prevent them from getting enough sleep, which may have irreversible long-term health impacts.

What Happens When You Don’t Get Enough Sleep?    

When people don’t get enough sleep, their bodies and mind are exhausted, which can lead to serious physical, mental, and emotional health issues. People who do not sleep enough tend to experience tiredness and fatigue during the daytime, sudden mood swings, difficulty concentrating and remembering things, and poor hand-eye coordination.

Lack of proper sleep can increase the risk of many health issues, some of which might even be fatal. People who do not get enough sleep tend to suffer from problems like a weak immune system, increased risk of type II diabetes, obesity and cardiovascular problems, and even mental health issues.


Researchers have just started to unravel the mystery of how sleep works. Despite the limited information available, sleep is quite clear among the most important body functions. Getting enough and proper sleep can enhance other body systems and functions quite significantly and help people lead a better and fitter life.


What happens when you sleep too much?

Although a good night’s sleep is essential. Numerous health issues, including diabetes, heart disease, and an elevated risk of death, have been connected to excessive sleep over a long span of time.

How much deep sleep do you need?

The average adult needs seven to nine hours of sleep per night. Of that period, between 13% and 23%18 should be spent in deep sleep. You spend between 55 to 97 minutes per night in deep sleep if you receive seven hours of sleep each night. The body can self-regulate how much deep sleep it gets.

How long is each sleep cycle?

An entire sleep cycle lasts between 90 and 110 minutes. Your initial REM sleep is short. You’ll experience more REM sleep and less deep sleep as the night goes on.

At what stage of sleep do you dream?

An hour to an hour and a half after falling asleep, REM sleep begins. When you’re in REM sleep, you often have vivid dreams.

Does resting in bed count as sleep?

No, resting in bed with your eyes closed doesn’t count as sleep. However, even staying quiet and relaxing in bed is beneficial for one’s health. Unless you are way too stressed or exhausted, you’ll likely sleep within minutes of laying down on the bed.


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