How Sleep Works & Understanding The Sleep Cycle

How Sleep Works
Sleep is a period of rest that's necessary for maintaining both mental and physical health. This complex biological process comes with innumerable benefits, such as giving our bodies time to repair damaged tissues and helping us integrate new information. Besides, getting enough sleep can improve your relationships, help you become more optimistic, and feel more rested.

But the big question is: What really happens minutes after you get into bed and fall asleep? Do your body and brain shut down completely, or will they remain highly active during this state of rest?

Read on to learn more about what happens when you sleep and the benefits of getting enough sleep

Understanding Sleep: The Sleep-Wake Cycle

This is the body's natural rhythm of interchanging different periods of sleep and wakefulness. Many factors play a pivotal role in preparing your body and mind to sleep and wake up. For instance, the circadian clock and your body's sleep drive send inputs to an intricate body system to help your brain regulate the sleep-wake cycle.

Sleep Drive

Your body has a biological demand for sleep that builds up the longer you stay awake. Once you fall asleep, this urge dissipates until you wake up, and the process starts again. All this is controlled by homeostasis, a process that keeps your body system, like your internal body temperature, steady.

Another compound known as adenosine is also connected to this need for sleep. During the day, while you're awake, adenosine levels in your brain continue to rise, signaling a shift toward rest. Taking stimulant drugs, such as caffeine, can interrupt sleep drive by blocking adenosine. Also, the amount of drive you accumulate will affect sleep intensity and how long you sleep.

Circadian Clock

Human beings have internal body clocks located in the brain that control when they're awake and when to sleep. These central circadian clocks have cycles of about 24 hours (circadian rhythms) and are impacted by multiple factors, such as sleep schedules, light, and darkness. Once you fall asleep, you cycle through different stages of sleep in a predictable pattern. However, this is a bit different from infant sleep as babies' sleep patterns tend to change depending on the stage of growth. 

Light-dark Cycle

The light-dark cycle controls how your brain makes and releases melatonin, a hormone that promotes sleep. It travels to your body cells through the bloodstream. The amount of melatonin in your blood starts typically rises in the evening and decreases early in the morning. However, exposure to artificial light can prevent your brain from secreting melatonin, thus making it hard to fall asleep.

As you're exposed to light, your brain transmits the signals to the other body parts through the sympathetic and parasympathetic systems. Your body then releases cortisol hormone, which naturally prepares you to wake up.

Problems With the Sleep-wake Cycle

Some people have issues with their sleep-wake cycle, meaning their brain can't keep them asleep or awake at appropriate times As specified by the American Sleep Association, about 40 million people experience sleep disorders every year.

Another 20 million suffer from occasional sleep issues. These dysfunctions cause sleep deprivation, which leads to problems with school, work, and social activities. There are over 70 sleep disorders. Some lead to making sounds and moving around (disruptive sleep disorders), while others overlap with psychiatric conditions.

Related content: Sleep and travel

Examples include:

Insomnia - People who have insomnia have difficulty falling asleep, staying asleep, or both. Other symptoms include headache, depression, slowness in activity, and lack of concentration.

Narcolepsy -
This is a chronic sleep disorder that causes excessive, uncontrollable daytime sleepiness. Hallucinations and sudden loss of muscle tone might also occur.

Sleep apnea -
A potentially severe sleep dysfunction in which you experience periods of interrupted breathing. This condition is more common in men. Risk factors include obesity and age.

Having problems with your sleep-wake cycle isn't always because of health issues. Sometimes, it's because the circadian clock isn't aligned correctly with your sleep time. Such instances include;

Jet lag -
This is a temporary sleep disorder that affects those who travel across multiple time zones. Some of the common symptoms include fatigue and difficulty concentrating.

Shift work disorder -
This condition mainly affects people who work at night, early mornings, or rotating shifts. It may either cause excessive sleepiness while you're at work or insomnia when you attempt to sleep.

The timing and rhythm of your internal clock also decline with age. Brain cells that promote sleep start to reduce as part of normal aging. Plus, certain health conditions like Alzheimer's disease can speed up the rate of neuron loss, making it harder for older people to stay asleep. Other factors like less physical activity can also affect circadian rhythms.

Stages of Sleep

When you fall asleep, your brain doesn't merely go offline. Instead, a series of events put it to sleep in stages. You cycle through two sleep phases each night, the rapid eye movement and the non-rapid eye movement sleep. These sleep cycles start over every 90 - 100 minutes and last all night long.

Non-REM Sleep

Non-rapid eye movement sleep has three sleep stages;

Stage 1

This is the transition stage from wakefulness to sleep. It's characterized by the slow movement of your eyes behind the eyelid and cessation of muscle movement. This is a stage of light sleep where you're still aware of the things happening around you. You can easily be woken by noises and other disturbances.

Stage 2

This is the stage where you're fully asleep and unaware of the things going on in your surroundings. Your heart rate, breathing, body temperature drops, and your eye movements either stop entirely or slow down.

Stage 3

This stage is known as deep sleep or slow-wave sleep. Here, muscles relax, breathing slows even more, and brain waves drop with only a few blow-ups of activity. It's hard to be awakened from this stage of sleep, and you might feel disoriented if any disturbance pulls you out of sleep.

Deep sleep is very crucial as your body heals itself during this stage. It builds muscle tissues, heals wounds, and replaces cells.

REM Sleep

This is the deepest and final stage of sleep. It happens about 90 minutes after falling asleep and is characterized by intense brain activity. It's also associated with vivid and active dreams. Just as the name suggests, your eyes during this period and breathing become shallow and rapid.

Heart rate and blood pressure also increase, but your muscles become limp, so you can't act out your dreams. The main purpose of this stage is to stimulate parts of your brain that are necessary for memory and learning and sorting and storing information. You can experience approximately three to five stages of REM sleep each night.

Why Is Sleep Important?

The function of sleep has puzzled scientists for years, but modern research is now giving new clues about what sleep does for both your body and mind. It serves a crucial role in well-being and good health throughout your life.

So, why do we need sleep?

Sleep serves to clear waste from your rain, reenergize your body cells and support learning and memory. What's more, it even plays a role in regulating appetite, mood, and libido.

Here's how sleep affects other parts of your body system.

Heart and Circulatory System

Your heart rate and blood pressure fall during the night when you enter non-REM sleep. Your parasympathetic system controls the body, and the heart doesn't do as much work as it does when you're active.

On the other hand, during REM sleep and when you start to wake up, your body activates the sympathetic system, thus increasing your blood pressure and heart rate.

People who don't get enough sleep or wake up frequently at night have a higher risk of;

  • Stroke
  • Obesity
  • High blood pressure

Problems With Thinking and Memory

Having a good night's rest helps with learning and the creation of long-term memories. If you don't get enough and quality sleep, you may end up having trouble focusing on tasks and thinking out clearly.

That's why adults are always advised to sleep between seven to nine hours a night. However, sleeping more than nine hours isn't necessarily harmful. In fact, it may be beneficial for young adults and patients who're recovering from sleep deprivation.

How much sleep young children should get revolves around their age. For example, babies four months to 1 year need about 12 to 16 hours of sleep per day. Sleep experts recommend naps for children below the age of 7.

On the other hand, an 8-hour sleep is enough for teens under the age of 18 years.


How your body handles fat greatly varies depending on circadian clocks, such as those in the muscles, fat, and liver. For instance, the circadian clocks prepare your liver to break down fats at appropriate times.
According to various sleep studies, not getting enough sleep can lead to;

  • Increased consumption of food
  • Decreased physical activity
  • Metabolic syndrome
  • Increased levels of leptin and ghrelin hormone


Your body secretes different types of hormones that are related to your circadian clocks and sleep pattern. In the morning, it makes the cortisol hormone, which promotes alertness and helps you wake up.

Other body hormones are controlled by 24-hour patterns that keep on changing throughout your life. For instance, the hormones that prompt the glands to release estrogen and testosterone are created in pulses at night, which get bigger as kids approach puberty.

Related content: Establishing Good Sleep Hygiene

Ready to Improve Your Sleep?

There's nothing quite pleasing like waking up refreshed after a restful night's sleep. While you may not be able to control factors that can interfere with your sleep, there are habits that you can adapt to encourage better sleep.

This includes sticking to a sleep schedule, creating a restful environment, and limiting daytime naps. You can also go through various mattress industry statistics to put yourself in a better position of choosing the best mattress for your comfort needs. If you often have trouble sleeping, it's wise to contact your doctor, who can identify and treat any underlying cause of poor sleep, giving you the good night's sleep you deserve.

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