Defining Sleep

People were always intrigued by the condition of sleep and tried to find out what happens to our body while we are sleeping.

If you would have to define sleep, how would you describe it? Is it a need, urge, satisfaction, inevitable waste of time or something else? We all experience it, but we also treat it differently, depending on our habits and priorities.

What is sleep and why do we sleep? What are dreams? What happens when we fall asleep? Those and many other similar questions have been current since the beginning of time. People were always intrigued by the condition of sleep and tried to find out what happens to our body while we are sleeping. In today’s post, we are going to explore the mysteries of sleep by going way back into the past to see how sleep was perceived in ancient times and to check some medical definitions of sleeping.


Sleep in Ancient Times

Since the Egyptians are the oldest civilization in history, we decided to start from them, from the very beginning. The Egyptians used hieroglyphics, a pictorial letter, so let’s check how they presented sleep. They used a combination of two words/signs, the word qed was depicted as a bed, and it denotes sleep, and the other word is resut which means to come awake, shown as an open eye which represents the dream. Combining symbols of bed and open eye, we get an expression awaken with sleep, which corresponds to the early descriptions of similarity between dreams and wakefulness.

Ancient Egyptians believed that every person has five bodies, and they also thought that the soul (ba) could go away from our physical body during sleep. In that way, sleep was in some aspect considered similar to death, since they believed in the afterlife, for them death meant that the person went to a different world. Sleep was one of the ways to reach that mysterious other world and communicate with people who have passed away. They had an idea that the deceased was sleeping, so they thought about their tombs as houses and their chamber rooms as bedrooms.

Just like many other cultures, Egyptians were fascinated by dreams, and they believed that the gods were sending them messages through dreams, to help them make decisions, cure an illness or to guide them through life. Egyptians also had a dream book, a book in which all possible dreams were described and interpreted; one of them is kept in the British Museum in London. Interpretation of some dreams varies from one culture to another, so it interesting to see how did they describe them according to their culture.

The ancient Egyptian medicine was also aware of sleep disorders, which is an interesting fact since their medicine is one of the oldest documented scientific disciplines. Many healing rituals, diets, and even surgical treatments were described on papyrus. On one of the found papyri, it was explained how ancient Egyptians used poppy seeds as a hypnotic which relieves symptoms of headache and insomnia, but also how it was used as an anesthetic. In some other papyrus, Egyptians recommended a herb called Thyme, as an excellent cure that can reduce snoring. It is clear that the ancient Egyptians knew more than a few things about sleep medicine, but many mysteries and secrets of sleep and Egyptian people are yet to be discovered.

If we move forward in time, to the period of ancient Greece, we can see that sleep was also one of their preoccupations. Famous Greek philosopher, Aristotle, even wrote a small treatise On sleep, around 350 B.C., in which he discusses three stages of sleep. But besides him, many other theories about sleep and dreams were written by ancient Greek poets such as Homer, Pindar or Hesiod. Greek philosophers turned sleep and dreams into a part of their philosophical researches, pre-Socratic philosophers like Democritus and Heraclitus proposed a theory about the naturalistic origin of sleep and dreams. On the other hand, Pythagoras claimed that dreams have a divine origin. That makes it clear that sleep was always a fascination of many scientists and philosophers as some phenomenon.


Medical Definition of Sleep

When it comes to the medical point of view, sleep represents the body’s natural rest cycle. Sleep cycles are different stages of sleep through which we all go through around five times each night while sleeping. One sleep cycle can last from 90 to 120 minutes, and it represents our progress from NREM stages to the final REM sleep phase, the first cycle during the night is the shortest one, and it lasts around 90 minutes, others last at least 100 minutes. During the state of sleep, an increased brain activity occurs, brain cells work slower but with much higher intensity. It has been estimated that we spend ⅓ of our lives sleeping, so just this fact shows us how important sleep is.

Every night almost all of us experience for hours this state of unconsciousness while we are resting. About 80% of our sleep time is dreamless, and this phase is known as non-REM (non-rapid eye movement) sleep. While at the NREM stage, our body pressure, heart rate, and breathing are low and regular, and our body is relatively still. The sleep cycle has four stages:

  • Level 1 – this stage represents the lightest phase of NREM sleep which can easily be disrupted. It is a transitional phase of falling asleep, something between wakefulness and sleep. Slow eye movements are present during this phase.
  • Level 2 – this stage makes around 50% of our entire sleep time and this actually the first stage of NREM sleep. Sleepers cannot awaken so easily like in the level 1 stage, and while they are in it their heart rate and breathing slow down, body temperature starts to drop down, and eye movements discontinue. Brain waves go slower, but sudden bursts of activity known as sleep spindles commingle with K complexes and both of them are keeping us asleep and safe from premature awakening.
  • Level 3 – it is the deep and restorative phase of NREM sleep. During this stage, some parasomnia sleep disorders such as sleepwalking, sleep talking or somniloquy can occur, but arousals or awakening are rare, and it is not easy to wake up a sleeper while he is in this phase.
  • Level 4 – in this stage we are already at deep REM (rapid eye movement) sleep, so it basically is not a part of NREM, but they together conclude a circle of the sleep cycle. During this period, blood pressure rises, breathing becomes irregular, shallow and rapid, heart rate and brain waves increase and act just as like they do when we are awake. We usually dream during this phase, but we do not always remember our dreams on the next day. However, if the sleepers get awoken during the REM sleep, they would most likely remember what they dreamed about.


Sleep Cycle Length by Age

Since our age dictates our needs and lifestyle, the amount of sleep that we require for normal functioning also changes as we age.

  • Newborns (0 – 4 months) – at this early stage of life, newborns sleepover the majority of their day, approximately they sleep from 14 to 17 hours, but not consecutive. Their sleep is categorized as active, quiet or indeterminate. Active sleep is considered to be equivalent to REM sleep.
  • Infants (4 – 12 months) – at this stage they can develop and follow sleep patterns, and they usually sleep from 12 to 15 hours.
  • Toddlers (1 – 3 years) – with an established sleep routine, they should reduce the number of daily naps to one, and sleep around 11 to 14 hours.
  • Preschoolers (3 – 6 years) – they need to sleep from 10 to 13 hours, if a nap cannot be avoided, try scheduling it during the afternoon, so that it does not hinder bedtime.
  • School-aged (6 – 13 years) – kids at this age should sleep from 9 to 11 hours, and that is essential for them at this age because the restorative processes and release of growth hormone occur while they are sleeping.
  • Adolescents (12 – 18 years) – approximately 8 to 10 hours of sleep should be enough but is essential for them to stick to their sleep routine since at this age teens tend do develop sleep disorders.
  • Adults (18 – 64 years) – with age we reach that boundary of minimal 7 to 9 hours of sleep per night. But with age, we also get some new responsibilities or start working shift jobs which can all disrupt our sleep. Many adults are sleep deprived and sleep less than recommended 7 hours, but just because they are grown up that does not mean that their body stopped working for them during the night.
  • Elderly (65 +) – many seniors sleep less once they retire, worries, emotions, illnesses, and sleep disorders tend to disrupt their much-needed sleep.


What Happens While We Sleep?

Although when we are sleeping we barely move or consciously do anything, our body is actively restoring and working, so now we are going to check through which processes our body is undergoing while we are snoozing.

  • Brain – for decades, even centuries, scientists believed that while we are sleeping our brain is resting too and being inactive. Some newer researches from the past 60 years have proven that that theory is wrong and that our brain is highly active even when we are not aware of it. Since then a lot of progress has been made in the field of understanding how our brain functions. We already explained how NREM and REM part of sleep cycle look like, but it is interesting to point out that although we have many similarities with some animals, particularly with mammals, there is some difference when it comes to sleep. When we sleep, our entire brain is involved, but, for example, whales and dolphins stay conscious while they are sleeping. Since they have to go to the surface to breathe, only one hemisphere of their brain is asleep at a time while the other one remains conscious.
  • Breathing – while we are awake, our breathing is usually irregular since it is affected by our speech, posture, exercise, emotions, and so on. But as we start falling asleep, our breathing pattern comes in order, and it becomes slower and more regular. During the REM phase, our breathing tends to get more variable again.
  • Physiological activity – many physiological activities slow down and decrease during sleep, like urine production or kidney function. But some other processes continue to work regularly or even with increased activity. Probably the biggest change that is caused by sleep is the increased release of growth hormone, besides that cell repair is also very active during the shut-eye period.
  • Temperature – our body performs a process called thermoregulation which includes a set of control mechanisms like shivering or sweating. When we are laying in bed, ready to fall asleep, our body loses some heat, and scientists even believe that that induces sleep. During the sleep, our body temperature drops for 1 or 2 Fahrenheit degrees, and in the REM phase it falls to its lowest point, and we are entirely functioning without the thermoregulation for those 10 to 30 minutes in REM.
  • Dreams – most fascinating but at the same time, the least understood process that occurs while we are sleeping are dreams. While dreaming, our thoughts follow some bizarre and illogical trail of the events that may be completely random or connected to something that we already experienced awake. Scientists have not yet succeeded to find a logical explanation for our dreams, so this area stays a mystery and a field open for researching.



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