Understanding the Human Sleep Cycle

Home Biology Understanding the Human Sleep Cycle

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By Trista - February 29, 2020

One of the few biological urges that we cannot control is sleeping. For many of us, waking up to an alarm clock is the worst thing, but we still have to do it. It relaxes our mind and body from a tiring day. Sleep gives our bodies time to recover and rejuvenate, and it does the same to our minds. But the brain does not sleep. Rest is not a time when our brain goes dormant. Even though we are not conscious during sleep, our mind is active. The proof lies in the fact that our bodily functions are active as we sleep. We still breathe and move, our heart pumps blood, the digestion system still works, and we see dreams too.

But the question is, even though sleep is an integral part of our life and a vital bodily function, how much do we actually know about the time we sleep? There have been innumerable amounts of research done regarding sleep, including the various stages of sleep, sound sleep, disturbed sleep, circadian rhythm, dreaming, and a lot more. It cannot be said that all is known in this regard, but we do have certain information. Further in the article, you will read about how your body knows when to sleep, why you dream, how dreams affect you, why dreams are important, and all of the stages of sleep.

Understanding the Human Sleep Cycle — *We inevitably go to bed every night, but do we have to? Photo Credit: wavebreakmedia/Shutterstock*

Why Do We Need Sleep?

A good night’s sleep is the best way to energize yourself. Not sleeping well can result in a bad, tiresome day. Going without sleep for long periods can actually make you psychotic and can also be fatal. Only after 3 to 4 nights of going without sleep, do people start to hallucinate, and after 7 to 8 days, it’s nearly impossible for them to live. Thus, it is clear that sleeping is essential to living as well as bodily functions. Even so, the reasons why we need sleep are still studied by the greatest minds.

There have been a few theories on why we need sleep, but none of them have given solid proof of the reasons. Some say it is important to establish our memories for the long term as the brain goes through a lot during the day, and these events need to be processed during sleep. Also, our bodies require time to repair any tissues or muscles physically. The body gets tired during the day accomplishing various tasks. Sleeptime is the time for our body to relax and repair itself. Sleep rejuvenates the body and mind to prepare it for the coming day.

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Circadian Rhythm

Our internal clock or biological clock, as we say, is synchronized well with the rising and setting of the sun. Many of the internal functions and systems of the body work as per the coming and going of natural light. Messing up with this can cause a lot of harmful effects on our minds and body. That is why people who work at night and sleep during the day have a weaker immune system and are more prone to diseases as they suppress their biological clock and do not follow a natural rhythm.

Circadian rhythm is basically a daily cycle that everybody tends to follow, including sleeping, eating, and mating. There are specific points in the day when you feel sleepy and at certain times when you feel hungry. That is your circadian rhythm. Natural light causes our heart rate and blood pressure to rise while suppressing the release of hormones like melatonin. Thus, helping us wake up and stay active throughout the day. Following our biological clock helps strengthen our immune system and keeps us healthy. It makes us more alert and our minds more active.

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Stages of the Sleep Cycle

The time we sleep consists of sleep cycles with an average duration of 90 to 120 minutes. No matter how well you sleep, if you think that once you get into a deep sleep, you get out of that zone directly in the morning, you are wrong. We go through several sleep cycles during the night, and each cycle spans approximately 90 minutes. The cycle consists of 4 stages, including stages 1, 2, and 3, or the NREM sleep (Non-Rapid Eye Movement) and the REM (Rapid Eye Movement). After the fourth stage, we start over with Stage 1.

Generally, we go through 4 to 6 sleep cycles every night. During the first 2-3 cycles, we spend more time in the NREM stages of a deep sleep, and during the last 2-3 cycles, we spend more time in the REM zone with less time in NREM stages. Waking up in the middle of a sleep cycle can cause a tiresome and dizzy day and may also give you a heavy feeling. Completing the sleep cycle is essential for the better functioning of your brain and body. That is why they say while taking a power nap; you should wake up within 20 minutes, or else you would drift off to deep sleep. Waking up in such a zone would leave you disoriented.

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Stage 1

The first stage is the NREM stage. This is the earliest phase of sleep when you are still alert and can be awakened easily. It may be termed as the transitional phase. You enter a stage of dizziness but are relatively alert to any external impacts. The brain starts producing alpha and theta waves in this stage. In this stage of sleep, you may experience vivid sensations and strange bodily experiences like falling from a long distance. These sensations are known as hypnagogic hallucinations.

Another experience, known as a myoclonic jerk, also occurs at this stage. This is when you feel startled suddenly during sleep or experience body jerks for no reason. Though it may seem uncommon, we experience this phenomenon more than we realize. The first stage of sleep lasts for approximately fifteen minutes, after which we move to stage 2 of sleep. If someone wakes up during the first stage of sleep, they may even feel like they were not asleep at all.

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Stage 2

Stage 2 is a relatively more in-depth phase of sleep than stage one. Here, people start to become less aware of their surroundings. Body temperature also drops, and the heart rate is regular. Your body is being prepared for deep sleep at this stage. It is a more stable stage of the sleep cycle between 45 to 55 percent of the entire sleep is spent. In this stage of sleep, there are quick outbursts of rhythmic brain activities, which are known as sleep spindles.

There has been recent research by Matthew Walker and his team that says that sleep spindles are connected to refreshment and our ability to learn. The research also means that the greater the spindle activity, the better the learning ability of a person will be. The longer duration of this stage is significantly crucial for our development. If the spindle activities are reduced, it may result in the reduced learning ability of the concerned person.

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Stage 3

The most restorative stage of sleep is the third stage of sleep. During this deep sleep stage, the body repairs its tissues and bones and also makes the immune system stronger. The deep sleep stage is responsible for the refreshment and repair of the physical body. It is also responsible for growth and development. This is when delta waves begin to emerge, hence this is also known as delta sleep. The muscles relax, and we drift into a deeper sleep. It lasts for approximately fifteen minutes.

As the body becomes less responsive, if a person is woken up in the third stage of sleep, they may feel out of place and disoriented for some time. Heartbeat and breathing rates are lowest during the deep sleep phase. It is during this stage that phenomena like sleepwalking, night terror, bedwetting, and sleep-talking occur. The third stage acts as a transition between the NREM stages and the REM stage of sleep and is least affected by external stimuli.

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REM

The fourth stage in the sleep cycle is the Rapid Eye Movement Stage. In this phase, your eyeballs scurry in different directions under the closed eyelids. The eye movements may or may not be due to intense dreaming. It cannot be clearly stated yet. This is the stage where the brain is most active, and the muscles of the body become more immobilized. REM is the stage when dreaming happens most often and with the most intensity.

Heart rates increase, and breathing becomes faster, but the muscles of the body are most relaxed. This is really important as otherwise, our body would react as per our dreams, and that can cause many accidents. In the first cycle, the REM sleep is short, but it gets longer in the later cycles and can extend up to one hour. Hence there are more chances for you to remember the dreams that you see in the latter part of the night. REM sleep phases are highest in childhood and are extremely important for the developmental functions of the brain.

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Changes in the Sleep Cycle with Age

The sleep cycle varies along the whole lifespan of an individual—the timing and duration of the sleep cycle change with age. In children, it is said to be 60 minutes, and then as the person reaches the age of 3, the sleep cycle increases to approximately 90 minutes and sometimes up to 120 minutes. Newborns have more NREM or active phases of sleep that aids with frequent feeding. Once they reach the age of 4 months, the sleep phases become a little more prominent. Toddlers spend more time in stage 3 and in REM sleep, and the same applies to preschoolers.

For school-age children ages 6 to 12, the deep sleep phase is most important as it helps in the physical energy restoration and development of the child. As a child gets older, more time is spent in stage 2 of the sleep cycle than in any other stage. The duration of the sleep cycle increases with age and the older the person, the less time spent in the REM stage. Thus the sleep cycle varies from person to person and is different for every age group.

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What is Dreaming?

Not all is known about dreaming, but the scientific community has theorized a lot about it. After years of research and work by scientists, we have come to know that though maximum and most intense dreaming occurs in the REM stage of sleep, dreaming can pretty much happen at any stage. The dreams that occur in the latter part of the night are longer, and thus, people tend to remember those more. Also, dreams may not occur at all during any stage sometimes.

To define what dreams are, we can say that dreams are a series of images, emotions, and sensations that occur in the subconscious state of mind. These are basically stories that our mind creates while we are asleep. It is said that each and every person dreams 3 to 6 times every night, but many have reported that they do not remember any dreams. Dreams may be from distorted memories or something like a fantasy. Dreams can be positive or negative. Negative dreams are known as nightmares.

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Freud’s Theory of Dream – Why Do We Dream?

Our waking life is full of emotions, wishes, fear, and traumas that our minds sometimes cannot consciously handle. Thus we tend to repress it all. During the night, there is less automatic repression. Therefore, the repressed thoughts, emotions, and fears would all start to appear on the surface. It may become so heavy for us that we would repeatedly wake up and would suffer from sleep deprivation. Famed psychoanalyst Sigmund Freud proposed that we all have sensors to protect our sleep and not let these repressed emotions in check.

But the pressure could then build and may lead to a psychotic breakdown. Thus dreamwork comes into the picture, which acts as an outlet to release the built-up tension without disturbing our sleep. Some of the repressed material is passed through this censor in an altered and more acceptable state. This will allow the rest to continue. This altered dreamwork is what we remember after we wake up and not the real repressed emotions and thoughts. Dreams, in a way, help us to balance our mental and emotional health.

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What Do We Dream About?

Though we may dream multiple times throughout the night, we don’t remember most of what we dream. Whatever little we remember about our dreams, we can say that dreams can be funny, entertaining, realistic, disturbing, meaningful, or bizarre. Dreams can also be repetitive. People dream about something that they have been doing repetitively for the whole day, people dream about their desires, people dream about things they fear, and also sometimes about weird stuff they think they have never seen.

The visions and images of dreams are mostly connected with what we have been through during the day. The images are compared with altered photographs of our desires and fears. Thus sometimes the dreams do not make any sense, but they definitely have some meaning. Mostly we cannot identify the meaning of our dreams as we don’t remember most of them.

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Lucid Dreaming

Have you ever been dreaming and realized that this is a dream? That is lucid dreaming. Lucid dreaming is one of the strangest phenomena that occur with us. Lucid dreaming is when we are in a half-conscious state, perfectly aware that we are dreaming. Recently popularized by movies like Inception, the most prominent fact that we accept is that we have somewhat control over our dreams when we are in a state of lucid dreaming.

Generally, dreams feel very real while we are in them, and we realize that it was a dream only when we wake up. In the case of lucid dreaming, we are aware that we are dreaming even when we are in the dream. Lucid dreaming also happens during the REM stage of sleep. Though it is unclear how many people actually experience lucid dreaming and how they do it, this phenomenon exists. One can also be trained for lucid dreaming.

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Nightmares

Negative, unpleasant, and terrifying dreams are referred to as nightmares. Though nightmares are reported more often in children, that doesn’t mean adults are safe from nightmares. It is in general that children remember dreams more than adults. As adults, we also have a tendency to repress anything that frightens us. Hence, we do not remember much of our dreams and nightmares. A few people even report recurring nightmares, where they see the same or similar images every time.

Nightmares should not be confused with night terrors. While nightmares leave a fear sensation in the body and mind at night, terrors cause screaming in the individual in sleep, which is not even remembered by them the next day. Negative dreams are more prominent than positive ones.

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Myths about Dreams

Dreams have been a part of our world and our civilization since the beginning of time. Every culture has tried to understand the reasons and meanings behind dreams and has built up its own theories regarding the same. The ancient civilizations believed that dreams are a way for the gods to speak to us. These theories have resulted in certain myths about dreams. Every culture and civilization has its own beliefs about dreams, but a few myths are worth mentioning here. All these claims have no proof and no research associated.

For instance, some civilizations believe that dreams are a glimpse of the future, and they act as a warning for upcoming events in life. Some believe that having a vision of certain things in dreams has particular meanings. For example, some believe that seeing someone dead in a dream actually increases their age. Dreams also signify a satanic symbol in a few cults and cultures. There have also been cases where if a dreamer claimed to see the future, they would be declared the worshippers of Satan and were killed. Dreams may or may not be relatable to what happened during the day, but they definitely should not be associated with such myths.

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What Influences Our Dreams?

There is a psychological aspect to our dreams that we can all agree upon. What we dream about depends on many factors, including our physical health, mental stability, and emotional vulnerabilities. Though not many people talk about it, our physical health has a high impact on what we dream about. For example, during the earliest stage of pregnancy, more vivid dreams are experienced. Thus, how you feel physically can impact the dreams that you see tonight.

Our mental stability and emotional state also have a significant impact on our dreaming. Dreaming is affected by our inner desires and even the fear we hold in our hearts. Mostly we dream about things that either are very repetitive in our life or about something we desire or fear the most and cannot face consciously. Dreams also process the little things that our conscious mind has avoided during the day, but our subconscious has caught them. Thus our thoughts, emotions, and attitude also influence what we dream about and whether those dreams are positive or negative.

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Do Dreams Have Meaning?

As per Sigmund Freud, dreams are a creative manifestation of the repressed emotions and thoughts in our brains that are smuggled through the censors between our conscious and subconscious minds. Our deepest desires and our greatest fears that we cannot deal with consciously are presented to us through dreamwork, thus releasing emotions and still giving us an option to ignore them entirely by stating them as bizarre dreams. But dreams do have meaning if you decide to analyze them.

Though there is no specific meaning of any symbol, pattern, or story that we see in our dreams, every dream means something to the individual who sees it. There is no common element that means the same for everyone. A particular set of visions in my dream may express one thing buried in my unconscious while the same features can mean something different to you. So dreams do have meaning, but the meaning is very individual to the person who sees the dream.

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Why Do Dreams Disguise Desires?

Dreams can be identified in three classes when it comes to desires. First, that manifests a non-repressed desire, second that manifests a veiled form of the repressed desire and third that has repressed concealed desires. These dreams may contain elements that may seem dreadful to you and can bring the dream to an end. Dreamwork in the second class of dreams has worked well to veil desires such that it does not break the dream or our sleep.

The manifest content in its veiled form expresses the desires that are looked upon or unacceptable at first glance in its original form. The initial form is known as the latent content which is the underlying desire behind the manifest content. These can be dreams of death or dreams related to unacceptable sexual desires that, if expressed in their original form, would disturb our mind and our sleep. Hence with the help of dreamwork, the latent content is disguised, and the repressed emotions also find an outlet.

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Dream Recall

Most adults claim that they do not remember their dreams. In fact, the only dreams they have are faded visions that they see during the last cycle of their sleep. Most people see 3 to 4 dreams every night but remember only 1 to 2 dreams in the whole week. Also, if these dreams are not recorded, the memories of these dreams even disappear, and the person does not remember anything about them. People at a young age remember their dreams more, and as age progresses, the ability to recognize and recall dreams reduces.

Sometimes the dreams that we see are so vivid that we can never forget them, and we remember such dreams even after years whether or not we recorded them in a journal. Dreams that are repetitive in nature are easier to recall with more details. Women tend to remember more dreams than men. The dreams that we can instantly connect to are more probable to be remembered than the bizarre ones. There are ways to remember dreams, and the more you focus on your dreams, the better you remember them. There are various techniques used for the purpose of dream journaling that can help you remember dreams better.

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Do Dreams Affect your Sleep Quality?

Dreams are natural to all individuals, and every night you see a few dreams, but not all of them affect your sleep. In fact, dreams are believed to protect your rest. Pleasant, entertaining, or positive dreams may not affect your sleep, but the negative dreams, nightmares, and bizarre dreams do. Also, lucid dreaming affects the quality of your sleep. Stress dreams occur when you have been very stressed lately, and such dreams can impact the quality of your sleep to a great extent.

If stress dreams or nightmares are regular to you and you keep waking up in the middle of the night, you may also develop sleep disorders. Extreme nightmares can also result in insomnia, and you may not be able to sleep for the whole night after such dreams. To be calm and relaxed before sleep is critical to help you avoid stress dreams, and nightmares, and it is imperative to improve the quality of your sleep.

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How Can You Sleep Better?

To start with, have a bedtime routine that is calming and relaxing. Whether it be nighttime meditation or just listening to some soothing music, you can also use aromatherapy, especially lavender oil, to aid in your relaxation. Try to avoid your phones and laptops for at least an hour before your bedtime. Avoid staying in bright lights just before sleep. Try to dim the brightness of your room for at least an hour before you go to sleep. This will aid the release of melatonin in your body, which helps you fall asleep. Reading a book can also help you fall asleep easier.

Some yoga and stretching may also help you sleep better. The food that you intake also impacts your sleep, so one should avoid caffeine and sugary treats before sleep. The thoughts and attitudes that you carry can affect your dreams a lot and may result in nightmares and stress dreams. To avoid this, we must deal with these thoughts and modify our attitudes to suit us more. So if you have a relaxed mind before sleep, you will sleep better and have less disturbing dreams, thus protecting your sleep quality.

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Sweet Dreams

Dreaming is an integral part of our lives, and though dreaming occurs mostly in the REM stage, it does not mean that there are absolutely no dreams in the NREM stages of sleep. Dreams act as a guardian to our sleep and help us sleep better. Not all dreams are bad, but the tendency to see negative dreams is more than positive ones. Dreamworks help us release the repressed emotions and thoughts in our subconscious in a more acceptable form. Thus the desires and fears do not disturb our conscience.

Some dreams can be controlled while others cannot. We cannot run away from our dreams, and whether we choose to analyze them or not entirely depends on us. We forget 90% of our dreams within 10 minutes of waking up, so if we want to remember some parts of a dream, the only solution we have is to write them as soon as we wake up. Many people maintain a dream journal as they believe their dreams help them understand themselves better.

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