Sleeping is one of the most important parts of our lives. Even though we don’t know why we need to sleep, we spend almost 33 percent of our lives sleeping. Proper sleep is as necessary as food and water for our survival. Most people believe that sleeping helps our brains to learn and create new memories, as well as keep us refreshed. Lack of sleep can make a person unresponsive, and an extended duration of wakefulness could adversely affect an individual’s health.
Sleep is also necessary to allow our brains to perform some important tasks, mainly optimizing neural communications. Even though a person shows little signs of activity while asleep, the brain is busy. An ongoing study suggests that sleeping allows our brains to carry out certain “housekeeping” duties while we sleep, particularly removing toxins that build up in our brains while we are awake. The reason behind why we sleep is unclear, but its effects are visible throughout our bodies. Sleeping influences every tissue and/or organ in our body, including the brain, heart, lungs, immune system, etc. It also affects our mood. A lack of sleep could lead to serious issues such as high blood pressure, cardiovascular disease, diabetes, depression, and obesity. So, now that we have the basic understanding of sleep, its effects on our bodies, and the problems that are related to lack of sleep, it is time to understand what happens when we sleep.
Parts of Brain and their Role in Sleep
Hypothalamus
Our brains have a small peanut-sized structure on the frontal lobe, which is called the hypothalamus. The role of the hypothalamus is to control our sleep-wake cycle. To do this, the hypothalamus relies on the suprachiasmatic nucleus (SCN), a bunch of thousands of cells that process the information related to light exposure and use it to control our behavioral rhythm. A person’s brain with a damaged SCN is unable to understand this rhythm, and as a result, such people can continue to sleep throughout the day even though SCN relies on the eyes to provide feedback about the light, blind people’s SCN function as effectively as normal people.
Brain Stem
The next part of our brain that plays a significant role in our sleep is the brain stem. It is at the bottom side of the rear portion of our brains. Brain stem communicates with the hypothalamus to control our sleep-wake cycle. There are specialized cells in the hypothalamus and brain stem which produce a chemical called GABA. The role of GABA is to reduce the activity of arousal centers in the brain stem and hypothalamus. The pons and medulla which are present in the brain stem have quite an important role in the REM sleep. They release chemicals that relax our bodies and put us in a paralyzed state to prevent us from acting while dreaming.
Thalamus
Thalamus, which acts as a relay between senses and cerebral cortex, is generally inactive while we sleep. However, it becomes active during the REM stage and relays information that is used to create the surroundings of our dreams.
Pineal Gland
Pineal Gland, which is located between the two hemispheres of our brain, interprets the signals sent by SCN and controls the production of the hormone, melatonin. The role of melatonin is to put you to sleep once your surroundings are dark. Some people who have lost sight and are unable to understand whether it is night or day are given melatonin supplements at night to help them to sleep.
Basal Forebrain
Basal Forebrain is located at the front bottom section of the brain and helps in controlling sleep and wakefulness. It works with the midbrain that acts as an arousal system. Basal Forebrain also regulates the production of adenosine, which helps in regulating sleep drive. Consumption of caffeine reduces the production of adenosine and helps you stay awake.
Amygdala
The Amygdala is a small nut-shaped part of the brain that affects our emotions, and it becomes active while we are in REM state.
Stages of Sleep
Now it’s time to understand the main topic of this article, the different stages of sleep. Our sleep cycle is divided into four stages. These stages consist of three levels of non-REM states and a REM state. Each of these states shows a different type of brain waves and neuronal activity. A person goes through the various stages of non-REM and REM sleep throughout their sleep duration. The duration of the REM state of sleep increases with the duration of sleep and is maximum around the morning. To put in a perspective, when we are awake, our brain waves show the maximum activity along with the muscle tone.
Stage 1 of Sleep
The first stage of non-REM sleep is the lightest state. A person in the first stage shows slow eye movements. A person in this stage can be awoken quite easily by external stimuli. This stage of sleep shows a decline in brain waves and relaxation in muscles. Some people might also experience what is known as a hypnotic jerk while drifting in and out of Stage 1 of non-REM sleep.
Stage 2 of Sleep
Stage 2 of sleep is the actual non-REM sleep where you are actually asleep. The state is devoid of any eye movement, and a person cannot be awoken as easily in stage 2 as in stage 1. The brain activities continue to show a decline with occasional spikes, which0 are called sleep spindles alongside sleep structures, which are referred to as K complexes. Sleep spindles, as well as K complexes, are believed to help the brain from waking up from sleep. At this stage, the body temperature and the heart rate are also reduced.
Stage 3 of Sleep
The third and final stage of non-REM sleep is called deep NREM sleep. This stage shows what are known as delta waves or slow waves. A person will rarely wakeup from sleep themselves, and a lot of external effort is needed to wake a person from this stage of sleep. Parasomnias such as sleepwalking or sleep talking occur at this stage of the sleep cycle. The muscles are relaxed, and the brain waves are slowest at this stage.
Stage 4 of Sleep
Stage 4 of sleep, which is actually called REM (Rapid Eye Movement), occurs for the first time around 90 minutes after you fall asleep. Your eyes show increased movement even though they are closed, and hence the name. At this stage, the brain becomes quite active, and the waves are quite similar to those of a wakeful state. The same is true about your breathing rate, blood pressure, and heartbeat. All the vitals show a similar pattern to that of the wakeful state. The REM state is the part of our sleep where most of the dreaming occurs. In this state, your muscles are paralyzed by your brain to prevent you from acting out in your sleep. The duration of REM state decreases as a person grows older, and memory consolidation occurs both in non-REM and REM states of sleep.
Sleep Cycle
A sleep cycle, as the name suggests, is a cycle where a person goes from non-REM stage 1 to REM stage and back to non-REM stage 1 again. The typical duration of a sleep cycle ranges from one and a half hours to two hours, and this occurs four to five times throughout the night.Even though it is called a cycle, a person doesn’t always go from stage 1 to REM stage in each cycle. There are multiple transitions between non-REM stage 1 to non-REM stage 2 throughout the sleep duration. It is only during the fifth or sixth hour of sleep that a person enters the REM stage.
Generally, a person starts at Stage 1, where the body begins to get relaxed, and there is slow eye movement. A person can be easily aroused at this stage. Stage 1 is needed as it clears the path for the next stage. Stage 2 of sleep is where you actually begin to sleep. This stage is achieved in 20 to 30 minutes after you fall asleep. Most people spend nearly half of their sleep duration in stage 2 non-REM sleep. Next comes the stage 3 of non-REM sleep. It is not as long as stage 2, and a person hardly spends 20 percent of their sleep duration in the third stage of sleep. However, children spend nearly 30 percent of their sleep in stage 3. As for the fourth and final stage, the REM stage can occur at any time during the sleep, but on average, it takes around a couple of hours for the onset of REM. Once you manage to reach the REM stage, the cycle becomes more regular and takes around 90 minutes to 120 minutes to complete. So, a person goes through four or five sleep cycles during an average of eight hours of sleep.
Dreaming in Detail
An important part of our sleep stage is dreams. Almost every living creature dreams in their sleep. A person spends nearly a couple of hours each night in the dream state. However, we forget nearly 90 percent of the things that we dreamed of when we wake up. Scientists haven’t figured out why we dream, but it is believed that dreams help us process our emotions. It is common for events from our day to appear in our dream, and maybe it occurs as our brain transfers data to long term storage. People can dream about a lot of things, and they could be happy ones or bad ones (nightmares). A person suffering from an anxiety disorder or depression is more likely to have a nightmare as compared to a healthy person. Dreams are most common in the REM stage, but they can also occur in stage 3 of sleep as well. People can dream in various ways, some dream in color whereas others dream in black and white (common for people who grew up in the era of black and white TVs) and even blind people dream.
Effect of Age on Sleep
Sleep changes as a person ages, the sleep requirement, and durations of a newborn, a toddler, a teenager, an adult person, and an old person are quite different. So, it is a good thing to know how age affects our sleep pattern.
Newborn & Infants
A newborn baby (up to 4 months) doesn’t show any distinctive brain wave patterns while they sleep. As their sleep pattern is different from an adult’s, we define the sleep stage of a baby as active, quiet, and intermediate. The active sleep of a baby is equivalent to the REM stage, and the quiet stage is like a non-REM stage. Most of the newborn babies sleep for 16 hours a day with a few hours of wakefulness to eat and poop. An infant (from 4 months up 1 year) starts to show actual sleep state as well as a sleep pattern. They sleep for up to 12 hours a day in a couple of naps ranging between 3 to 5 hours.
Toddlers
A toddler (ages between 1 and 3 years) shows a fully developed sleeping pattern. They spend the majority of their sleep in stage 3 (around 30 percent) and REM stage. A toddler typically sleeps for up to 10 hours a day. A toddler can sleep for a couple of hours during the day, with the majority of sleep taking place at night.
Early School Age
This group includes kids aged between 3 and 12 years. Children in this segmented sleep for 8 to 9 hours a day, and their sleep patterns are quite similar to adults. Proper sleep is needed by these kids to help in their growth and development.
Beyond 12 years
Once a person reaches an adolescent age, his or her sleep cycle becomes fixed until they become old. At this stage, we require 7 to 8 hours of sound sleep for proper functioning. It is highly uncommon for people to sleep during the day until they become really old when age-induced weakness makes it necessary for people to sleep a lot more than 8 hours a day.
Stages of Sleep FAQs
What Are the Different Stages of Sleep?
Sleep can be divided into four stages consisting of three non-REM stages where our bodies become relaxed and show a decline in vitals. The fourth stage is called REM, where our body shows similar vital signs as of wakeful state. Dreaming occurs in this stage.
Why Do We Sleep?
There is no proper explanation as to why people sleep, but researchers theorize that we sleep to let our brain perform some “housekeeping” activities such as transferring memories to permanent storage and getting rid of toxins built up during the day.
In Which Stage of Sleep Do We Dream?
Dreams are a lot common during the REM stage. However, a person can dream in a deep sleep as well. A person dreams for up to 2 hours per night, but most of it is forgotten as soon as a person wakes up.
How Long Should I Sleep?
The duration of sleep depends on the age of a person. New-borns and infants can sleep up to 14 hours a day; a toddler can sleep up to 12 hours (partially in the day and partially at night), young school going kids need to sleep around 10 hours (a couple of hours during the day), teenagers and adults need to sleep around 7-8 hours per night. Old people can sleep a bit longer due to the weakened body.
How to Sleep Properly?
To sleep properly, ensure that your bed is comfortable, your clothes are comfortable, avoid consumption of caffeine before sleeping and keep away gadgets and turn off the lights. If you face trouble while sleeping at night, please consult a doctor.
