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Stages of Sleep


Last Updated on July 9, 2020 by Ben Locke

Sleep, quite naturally, constitutes a very important part of your routine. A person, on average, spends one-third of his daily time sleeping. It’s not just enough to get quality sleep, the amount of time you spend sleeping has also proven to be as essential for survival as the intake of food and water. Today we are attempting to understand the stages of sleep to help you get an insight into this daily process, which we might be taking for granted. Sleep is important for numerous brain functions. It determines how our nerve cells are able to communicate with each other and also rids our brain of any toxins that it might have collected throughout the day. As a matter of fact, both your brain and body stay remarkably active during the time you are asleep.

Till now, it has not been determined exactly what leads our body to demand sleep. Sleep has an effect on every kind of tissue and organ in our body; this includes our brain, lungs, heart, our metabolism, mood, and immune function. Research has shown that people who suffer from chronic insomnia and lack of sleep are unable to get quality rest, which increases their vulnerability to disorders like high blood pressure, diabetes, obesity, depression, etc.  Sleep is a highly complex and dynamic process that affects our brain in ways that scientists are only now beginning to find out. Other than the stages of sleep, there are a number of things we have covered in this article, such as:

  • Science Behind Sleeping
  • Stages of Sleep
  • Mechanisms Involved in Sleeping
  • How Much Sleep is Enough
  • Changes in Our Sleep Cycle With Age
  • The Biological Factors Affecting Our Sleep
  • Tips To Sleep Better
  • Future of Sleep

Science Behind Sleeping

The act of sleeping first starts on a molecular level, through something called a neurotransmitter. This is a chemical that acts on your nerve cells and directs your brain to either sleep or stays awake. Once your neurons have told the body to go to sleep, you pass through various stages of sleep; but a lot happens before, as discussed below.


The hypothalamus is a peanut-sized structure that is placed deep inside our brains. It contains various groups of neurons or nerve cells that act as control centers that affect our sleeping or waking. Within this structure, there is another cluster of thousands of cells known as the suprachiasmatic nucleus (SCN). This cluster of neurons receives information about how our body is being exposed to light directly from our eyes in order to control our behavioral rhythm. There are some people who might have received some damage to their SCN because of which they sleep erratically through the day and are unable to coordinate the circadian rhythms with the light-dark cycle.

Brain Stem

The next structure responsible for our sleep is the brain stem present at the base of our brain. It communicates with our hypothalamus and controls daily transitions between sleeping and waking. In the hypothalamus and brain stem, are present sleep-promoting cells which produce a brain chemical called GABA. This reduced the activity of centers of arousal in the brain stem and hypothalamus. Other parts in the brain stem like pons and medulla also play an important role in REM sleep, like sending signals to relax muscles and stop limb movements.


Next comes the thalamus, which relays information from our senses to our cerebral cortex. In most stages of sleep, our thalamus becomes quiet and helps to tune out our conscious thoughts and the outside world. However, during REM sleep, our thalamus is active and sends cortex images, sounds as well as other sensations to make up our dreams.

Pineal Gland

The pineal is placed right within our brain’s two hemispheres. After receiving signals from the SCN, its function is to increase the production of the sleep hormone melatonin to help you go to sleep. People who might have lost their sight and, as a result, are unable to coordinate the natural wake-sleep cycle can instead take melatonin supplements to ensure that they get to sleep on time. Most scientists are of the opinion that the rise and fall of melatonin is important for the body’s circadian rhythm to the external cycle of day and night.

Stages of Sleep

Basically, the sleep cycle can be put into two categories: rapid eye movement (REM) as well as non-REM sleep, both of which have their own separate stages. These two stages of sleep are linked to specific neural activity as well as brain waves. While you sleep, your body goes through the cycle of REM and non-REM sleep several times. Deeper REM sleep periods typically occur towards the night.

Stage 1

Stage 1 of non-REM sleep constitutes the transmission between wakefulness and sleep. This is a short period and lasts for a few minutes. During this time, you sleep lightly and your heartbeat, breathing as well as eye movements remain slow. Your muscles begin to relax with occasional twitching. The brain waves become slower as compared to your daytime wakefulness hours.

Stage 2

Stage 2 of non-REM sleep constitutes a period of light sleep and, later, a transition into a deeper sleep. During this stage, your heartbeat, as well as breathing, slows down even further, and your muscles relax completely. The temperature of your body drops down, and all movements of your eyes stop altogether. Although the activity of your brain waves slows down, there are sudden, brief bursts of electric activity. More time of your repeated sleep cycles is spent in stage 2 as compared to other stages of sleep.

Stage 3

Stage 3 of non-REM sleep is the time during your deep sleep, which is needed by the body to feel fresh in the morning. It occurs during the long periods of the night, in the first half of your sleep cycle. Your heartbeat and breathing are at their lowest during this time. Your muscles are relaxed at this time, and it’s difficult to wake you up. Your brain waves turn even slower.

REM Sleep

After you have slept for about 90 minutes, you enter into the REM sleep stage. In this stage, your eyes show rapid movement from side to side under your closed eyelids. The brain wave activity is mixed, and the pattern matches the one seen during wakeful hours. Your breathing also changes to become faster and irregular; there are also changes in your heart rate and blood pressure, which almost rise to wake levels. The dreams that you have to occur mostly during REM sleep. However, there chances that you might dream during non-REM sleep as well. Your arm and leg muscles are temporarily paralyzed during this stage, which stops you from acting out your dreams. With age, you begin to spend less time in REM sleep and more in non-REM sleep.

Mechanisms Involved in Sleeping

There are two internal body mechanisms that go on in our body, which help us fall asleep. The circadian rhythm and homeostasis work in tandem to regulate the various stages of sleep that we have mentioned above.

Circadian Rhythm

The circadian rhythm directs a number of functions in the body, from daily changes in wakefulness to our metabolism, body temperature, and the release of various hormones. It also controls the tendency of our body to go to sleep at nighttime and helps it wake up in the morning, without the need for an alarm. Your body has a biological clock (which is almost the same as the 24-hour clock), and it controls most of the circadian rhythm. Circadian rhythm also coordinates with natural cues such as light and temperature, in the regular time of the day, but it functions well even without such cues.

Sleep-Wake Homeostasis

Sleep-wake homeostasis is responsible for keeping track of your need to sleep. The sleep drive during homeostasis is important to remind the body to go to sleep and regulate the intensity of sleep. Your sleep drive tends to get stronger every wakeful hour and helps you to go to sleep for long, deep hours, especially if you have been deprived of sleep for some time.

There are various factors that influence your sleep-wake homeostasis; this includes medical conditions, stress, the food you eat, medication, and even your sleep environment. The greatest influence on the sleep-wake cycle is your exposure to light. There are specialized cells in the retina of your eyes that process light and assist your brain in understanding whether it is day or night. The messages from these cells can delay or advance your sleep-wake cycle. If you are exposed to too much light (including blue light) before sleeping, you might find it difficult to fall asleep.

People who work at night find it difficult to sleep when they go to bed. They also find it difficult to stay awake at work because the natural circadian rhythm and sleep-wake cycle of their body is altered. Jet lag occurs when the circadian rhythm of the body is unable to coordinate with the natural 24-hour clock in a particular time zone.

How Much Sleep is Enough?

There is no definite number of sleeping hours, which is applicable to all people when it comes to deciding how much sleep we need. You might want to note that the need for sleep, as well as sleep patterns, change greatly as we age, and there is no magical “number of sleep hours,” which works even for people of the same age. Initially, babies start out by sleeping as much as 16-18 hours a day. This is important to boost the growth and development of their brains. Children, adolescents, and teens need at least 9.5 hours of sleep every night. However, as we turn old, particularly after sixty, our sleeping hours in the night tend to become lighter, shorter and are frequently interrupted by wakeful hours or minutes. Elderly people, also happen to take medications which affect their sleeping pattern. In the current times, people are mostly getting less sleep than they actually need because of longer working hours as well as the availability of distractions and entertainment, which are available round the clock.

Changes in Our Sleep Cycle with Age

Sleeping hours change all throughout our lives. We don’t spend any two nights getting the exact same amount of sleep. Below we have summarized the various changes that take place in our sleeping pattern as we grow from toddlers to adults.


Newborns who are up to 4 months old do not show any distinct sleep waves. Sleep is usually categorized as “active,” “indeterminate,” and “quiet.” Active sleep is the same as REM sleep, and quiet sleep is the same as non-REM sleep. Most of the time, newborns are in the stage of active sleep, which causes them to wake up many times during their sleep. This is important to maintain a feeding routine.


Babies, between the age of 4 months- 1 year, begin to show standard sleep stage distinction. During this time, sleep becomes more consolidated, and children begin to develop a sleep routine. Babies usually sleep for 10 to 13 hours while napping two or three times daily.


Children between the age of 1-3 years have completely developed sleeping patterns. Children now begin to spend as much as 25% of their sleep time in stage 3 of deep sleep and an equivalent amount of time in REM sleep. The average time for sleep among children is 9.5-10.5 hours per 24 hours. Typically, naps are seen reducing down to one time a day and occur in the daytime, to ensure proper sleep at night.


Children between 3-6 years have a sleeping pattern, which is much similar to that of toddlers. They sleep for about 9-10 hours every 24 hours, and most children forego their daytime naps. The amount of time spent in stage 3 continues to remain higher than the time spent in other stages.


Children who are between 6-12 years of age sleep for about 9-10 hours every night. Stage 3 comprises approximately 20-25% of the sleeping time. This is the age where restorative sleep is very important for growth and development.


Children and teenagers above 12 years of age need to sleep for about 9-9.5 hours every day. During this time, there are physiological changes in the circadian rhythm, which cause us to sleep later than usual. This internal shift in the body is the reason why many adolescents want to go to bed later than usual and prefer to sleep more in the morning.


As a person ages, the circadian rhythm is reset to normal again, and people are able to get as much as 6.5-8 hours of sleep every 24 hours.

The Biological Factors Affecting Our Sleep

Chemicals That Help Sleep

There are a number of sleep-promoting nerve cells in various parts of the brain which tend to become active as we prepare for bed. There are nerve-signaling chemicals in our body called neurotransmitters, which can shut down or reduce the activity of cells, which cause our body to be alert or relaxed. GABA  is one such chemical that is associated with sleep, sedation, and muscle relaxation. Norepinephrine and hypocretin or orexin help keep some parts of our brain active while you’re awake, and their production is lessened at the time of sleep. Other neurotransmitters that shape sleep include acetylcholine, adrenaline, histamine, serotonin, and cortisol.

Genes and Sleep

Genes might have a much larger role in helping us sleep than we might have guessed. Scientists today have identified a number of genes that are involved with sleep disorders and sleep. These genes are also capable of controlling the excitability of neurons while clock genes such as, cry, and time also affects circadian rhythm and the timings of sleep. Genome-wide association studies have discovered several sites on a number of chromosomes, which might be increasing our susceptibility to a number of sleeping disorders.

Also, some genes are now being associated with numerous sleeping disorders such as familial advanced sleep-phase disorder, restless legs syndrome, narcolepsy, and so on. Some genes which are present in the cerebral cortex or other regions of the brain change how much they are expressed while we are asleep or awake. Many genetic models, including the fruit fly, worm, and zebrafish, have helped scientists identify genetic variants and molecular mechanisms that are involved in sleep disorders.

Tips to Sleep Better

Getting enough sleep is crucial for your overall health. You can follow the tips given below to ensure that you get the rest that you deserve-

  • Set a sleep routine and schedule. Make sure that you maintain a regular sleeping and waking time every day.
  • Get at least 20-30 minutes of exercise at least one time during the day, but take care that you’re not working out soon before bedtime
  • Do not take caffeinated drinks, nicotine, or any other stimulants before going to bed.
  • Try to follow some relaxation routine before you go to bed. You might want to take a warm bath, listen to soothing music, or read anything you like before bedtime.
  • Make sure that you maintain sleep hygiene. This includes avoiding bright lights, loud sounds, and extreme temperatures before going to bed.
  • Don’t stay in bed if you have trouble sleeping. Instead, read a book or engage in some relaxing activity when you can’t sleep.

Future of Sleep

Scientists are today learning a lot about the regulation and function of sleep. A very important focal point of this research is understanding the risks which are involved with the condition of chronic sleeplessness. People who are unable to sleep well are more likely to get cardiovascular diseases, heart strokes, and even cancer. Sleep disturbances are particularly common in people of age who might have neurological problems like Parkinson’s disease or Alzheimer’s. It could be that the lack of sleep results in a number of disorders, or perhaps certain diseases cause sleeps deprivation. Many such questions are still waiting to be answered.

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