After a long day, everyone looks forward to coming back to their beds and getting some sleep that will recharge their energy levels for the next day of work. The act of sleeping comes naturally to human beings but have you ever wondered why do we need to sleep?
When you’re thinking along these lines, a valid parallel to draw is the process of eating. We eat because we feel hungry. Hunger is a protective mechanism that is unique to living beings that helps ensure that your body is getting all the necessary nutrients. These nutrients are essential for us to grow and function well. We eat when we feel hungry and the same goes for sleepiness and sleep.
There are powerful internal mechanisms that regulate both eating and sleeping. If you stay away from food for a long enough time, your body will send you signals that are in the form of hunger that you feel. Similarly, you will feel an overwhelming feeling of sleepiness if your body is kept without sleep. Eating food relieves hunger and gives us the nutrients we need, while sleeping gets rid of sleepiness and makes sure that we are more alert, energetic, happy and able to function well.
First, let’s go back to the basics!
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What Is Sleep?
This isn’t an easy question to answer. Sleeping is one of the most important aspects of our life but that doesn’t mean that defining this phenomenon is simple. The first technical difficulty that we face is that we can’t analyze our own sleep. Most people don’t even know that they’re asleep when they are sleeping. It is possible to observe others while they sleep but that does not give us as much insight into the changes in the functions of their brains and bodies as it cannot be seen from the outside.
Your sleep is controlled by neurotransmitters or these nerve-signaling chemicals. These chemicals are in charge of our sleep or our state of wakefulness. This is the result of different nerve cells being acted upon by these chemicals. The production of neurotransmitters like serotonin and norepinephrine is the result of activities that take place within the nerve cells or neurons present in the medulla oblongata that act as the connecting mechanism between the brain and the spinal cord. These neurotransmitters are the ones that keep parts of your brain in an active state while your body is awake. When we start to fall asleep, there are neurons that begin signaling towards sleep, and in a way turn off those particular signals that keep us awake. There is also research that suggests that adenosine — a chemical produced by the body — builds up in the bloodstream, causing us to feel drowsy. Sleeping breaks down this chemical gradually, making us feel more refreshed and energized.
Theories of Sleep
As discussed before, the exact reason why we sleep is tough to ascertain. There are, however, a number of popular theories regarding this that will be discussed below.
Inactivity Theory
The first theory that will be discussed here is also one of the oldest. The inactivity theory is also referred to as the adaptive or evolutionary theory. The basic premise on which this theory is based says that being inactive during the hours of the night is not something innate but something that is adapted by the human body in order to survive in this world. The reason behind this is that night time is when we are most likely to attract danger and sleeping during these hours would keep us safe. Keeping a low profile and staying inactive attracts less attention than being out and active during this period. This technique aimed at survival slowly evolved over the years into the activity of sleeping.
The most common critique of this inactivity hypothesis is that under regular circumstances, it is always better to stay in your senses if you want to tackle any emergency in a better way. Sleeping will not help you in situations where safety is what you are on the lookout for. It is almost always recommended that you stay awake and in control of your senses if you want to evade danger.
Energy Conservation Theory
One of the main factors that influence the way in which the world functions is the competition for resources, and stemming from that, the best utilization of a person’s energy resources. While it may not be as apparent today when there are a number of food sources around us, the energy conservation theory suggests that the main reason why we sleep is cut down on the body’s demand for energy and the way in which this energy is expended at the time when you aren’t looking for food — at night!
The rate at which the body metabolizes energy is reduced by a significant amount during sleep, which means that sleep helps living beings conserve their energy. This part of the energy conservation is closely linked to the adaptive or evolutionary theory.
Restorative Theories
This theory is built on the understanding that sleep serves to repair and reconstruct all that is lost by the body when we engage in the activities of the day. The act of sleeping gives the body an opportunity to put itself back together and feel refreshed after the wear and tear of the day.
The ideas propagated by the restorative theories have received backing from some empirical evidence that has been collected by studying a variety of living beings in the recent years. A great example of this are studies that show that animals that are completely deprived of sleep can lose a lot of their capability to restore their health, leading to death in a relatively short period of time. There has also been research that shows that a large amount of functions like the growth of muscles, repair of the body’s tissues, synthesis of proteins, or the release of growth hormones take place during the hours of sleep.
Brain Plasticity Theory
This theory is more recent when compared to the others before and offers a compelling explanation for the reason behind sleep. It is based on the premise that sleep is related to the changes in the way the brain is wired and functions — now to be referred to as brain plasticity.
While it is not understood entirely at the moment, this phenomenon is related to sleep and the way in which it works. An example of this is that it is slowly becoming clear that sleep has a very important role to play in the development of the brain when it comes to babies and young children. Babies sleep for prolonged hours and most of this is spent in rapid eye movement sleep (REM), the phase in which dreaming is most common. Even adults have shown similar links between sleep and brain plasticity in adults. An example of this is the way people lose their ability to carry out a number of tasks when they are feeling a distinct loss of sleep.
Stages of Sleep
While it may not be as easily noticed by a lay person, sleep occurs in distinct phases, all of which have their own specific features. There are five phases such phases. The normal progression of sleep is from the first stage and goes through four more stages before it reaches the REM sleep stage. The rotation starts again once a cycle is completed. Human beings spend most of their sleep – almost half – in stage 2 sleep, followed by about one-fifth in the rapid eye movement stage. The remaining part of your sleep is spent in the rest of the stages. The division differs with age groups. For example, infants spend a majority of their sleep in REM sleep.
Stage One
The first stage is light sleep. In this stage of sleep, human beings move into the state of sleep and out of it often. They can be woken up with relative ease. The movement of eyes is very slow and the muscle activity also reduces as you fall deeper. If you are woken up during this stage of sleep, you can remember some visual images or experience some sudden contractions in your body that are commonly felt as jerks. This is often preceded by the feeling that you’re about to fall. These sudden jerks are like the small shock that the body experiences when it’s startled. There are people who also experience a sleep disorder, referred to as PLMS, where the body engages in recurring leg movements.
Stage Two
This is the stage where the person’s eyes stop moving around. In stage 2 sleep, the brain waves become slower. These brain waves are basically altering levels of activity — electrical in nature — that is measurable by employing electrodes. The body also experiences the occurrence of sleep spindles or the sudden bursts of oscillatory brain activity, in this stage.
Stage Three, Four and REM Sleep
In this stage 3 of sleep, the body experiences these extremely slow brain waves or slow-wave sleep. These waves are not constant and the brain also experiences some smaller, faster waves in this stage of sleep. Following this, the body enters stage 4 of sleep. In this stage, the brain stops producing other waves and concentrates on the delta or slow-wave sleep. It is tough to wake up a person in these stages — stage 3 or stage 4 — of sleep, making these stages the ones in which your body is in deep sleep. The muscle activity and movement of eyes is reduced to minimal in these stages.
If you are woken up in the stages of deep sleep, you will be more likely to face difficulties in adjusting to your surroundings and feel dazed and muddled. It is common for children to experience bedwetting or night terrors during this phase of deep sleep.
Your sleep cycle is what affects the quality of sleep that you experience. The last stage is REM sleep, where the breathing becomes more rapid and irregular, causing your eyes to jerk around rapidly in various directions. Your limb muscles also become temporarily paralyzed during this phase. REM sleep is marked by an increase in heart rate, rise in blood pressure and cases of penile erection in males. REM sleep is also the phase where people experience dreams.
How Much Sleep Do We Need?
A good sleep is important for everyone, as it is the basic requirement for retaining information and developing skills to traverse life. It is even more important for children as it helps them in acquiring language, social and motor skills. While it is important to think about why does your brain need sleep, it is also important to see how much sleep you need.
This means that adults need between 7 and 9 hours of sleep every night, while infants need almost 11 to 14 hours or sleep. Children who are going to school require between 9 and 11 hours, while teenagers require between 8 and 10 hours of sleep every night.
The first time that you reach the stage of REM sleep is about an hour or an hour and a half after falling asleep in most cases. An entire sleep cycle takes anywhere between an hour and a half to almost two hours in most cases. The first few sleep cycles contain shorter periods of REM sleep and longer deep sleep periods but this is reversed as the night advances. This means that by morning, you will be spending almost of all your sleep time in stage 1, stage 2 and REM sleep.
On a similar note, there is research that shows the connection between sleeping too much and having too little energy.
Importance of Sleep
As we have already discussed the different theories about why we need sleep, it is also important to talk about the benefits of sleep in our lives.
Necessary for Survival
You may be wondering why do we need sleep to survive. While it is tough to point out why people need sleep, there has been a lot of research on animals that shows that sleep is necessary for survival. An example of this is research on rats which shows that they usually live for two to three years, if they are deprived of REM sleep, they can only survive for about 5 weeks on average. If rats are deprived of all sleep stages, they can only live only up to 3 weeks.
Helps the Nervous System Function Properly
There is research that shows that sleep may be necessary for the human nervous systems to function properly. Sleep deprivation leads to drowsiness, lack of concentration, impaired memory and reduced ability to solve math problems. There are experts who believe sleep allows neurons to shut down and repair themselves.
Growth in Children
Research shows that deep sleep coincides with the release of growth hormone in children and young adults. There are also a number of the body’s cells that show an increase in production and a reduction in the breakdown of proteins while the body is in deep sleep.
The exact mechanism behind sleep is still elusive but the importance of uninterrupted sleep cannot be challenged. Further research can be expected to bring in some much-needed clarity but till then, make sure you get a good night’s sleep!