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Sleep as a physiological process
“The main facts in human life are five: birth, food, sleep, love and death.” This quotation belongs to an English writer E. M. Forster. He equates sleep to the most essential life processes, as birth and death in particular. Furthermore, it refers not only to a human being, but also to mammals, fish, birds, etc. No wonder that this natural physiological process, which is characterized by the decrease of cerebration and reaction to environmental factors, has been interesting for scientists from ancient times.
Then, they could not define the nature of sleep and dreams exactly, that is why they proposed the theories which now seem funny and even ridiculous to us.
Several centuries ago, people thought that toxic substances were accumulating in a human organism during a day. In such a way, a man’s brain became poisoned and caused a state of partial malfunction of his/her consciousness – a man closed the eyes, became immovable for a few hours and after wakening shared with others with the pictures he/she had been seeing. Sleep was considered as a side effect of an organism’s poisoning.
Aristotle affirmed that sleep symbolizes approaching of death. Each person in this world is mortal. Every night he/she became one step closer to the end of this life.
However, such theories fell off the edge of the earth since the second half of the XX century when scientists began to consider a human’s brain as the center which is responsible for almost all processes in a human organism, including sleeping and dreaming. This new approach was introduced and developed by Charles Darwin and Sigmund Freud. Since then, they have begun to pay closer attention to this unique organ, which was not studied well. Technological progress let them do this.
What did the scientists discover about sleep and dreams?
A man spends approximately one third of his life sleeping. During this time, an organism’s processes are not put to a pause. On the contrary, some of them become more active while a man is sleeping. Furthermore, some health disorders can become apparent only in this state.
There are a few types of sleep which are cyclic and tend to repeat 4-5 times per night. Each of them has its own unique characteristics:
NREM (Non-Rapid Eye Movement; also, called “quiet sleep”)
REM (Rapid Eye Movement; “active/paradoxical sleep”)
In their turn, they are divided into four stages.
Stage 1(NREM): This stage is also known as “a catastrophe stage”. During it, your organism is preparing to sleep. It is somnolence that lasts 5-10 minutes. All images are floating in front of your eyes, everything seems indistinct to you, your thoughts get confused and you cannot distinguish reality from a dream anymore. Brain produces theta-waves which are very slow; your heart rate is slowed down in several times and the temperature of your body is also decreased; all muscles are totally relaxed.
This stage is a transitional one: you are falling asleep, but still you aren’t fully detached from reality. You must have experienced falling rapidly somewhere or hearing somebody’s voice while drowsing. These sensations are called “hypnagogic hallucinations”. They are the markers that you are experiencing the first stage of sleep at the moment.
Have you ever flinched when falling asleep? Sometimes, it can even wake you up. This phenomenon is called a myoclonic jerk, and it is one more feature of the very first stage of falling asleep. It is a brief and sudden contraction of muscles when a man is about to get immersed into sleep.
Myoclonic jerk can be shown when people hiccup, shudder with fright, flinch when they are falling asleep.
As it is mentioned above, some health disorders cannot become apparent when we stay awake, only when we are sleeping. The same is with myoclonic jerk. On one hand it is a common phenomenon which is totally safe. But on the other hand, it can be a symptom for a range of dangerous diseases: multiple sclerosis, Parkinson's disease, Alzheimer's, subacute sclerosing panencephalitis, Creutzfeldt-Jakob disease, MERRF syndrome and some forms of epilepsy.
Stage 2 (NREM): This stage of falling asleep by a human takes about 20 minutes. During it, you are drowning into sleep more and more (if no external factors disturb you). A brain produces rapid waves; temperature of a man’s body is continuing to decrease as well as his/her heart rate and metabolism. Your organism is starting to undo the damage it has sustained during a day.
Stage 3 (NREM): It is also known as delta sleep because of very slow waves (delta-waves) which produces our brain. This is a transitional stage between light and deep sleep. Your organism becomes more unreceptive to different external factors. That is why when a person has already entered this sleep stage, it is rather difficult to wake him/her up. Due to this peculiarity, bedwetting and sleepwalking may occur.
Stage 4 (REM): This stage is also called as active or paradoxical sleep because during this time our brain begins to work more actively (almost like when a person is awake), but the muscles become even more relaxed. Usually, it takes a man about 90 minutes to go into it. At this very stage we see our dreams. If to wake somebody up and ask him/her what he/she has seen in a dream, this person will retell you a dream in detail. But in the phase of NREM sleep, it will be much harder to do. Sometimes, it is impossible at all. That is why some people assert that they don’t see dreams at night. However, they are wrong. Everybody has dreams while sleeping. The thing is that not everybody can remember them.
The stages of sleep do not occur in sequence though. There can be the first three stages in a row, then you may return to stage 2 which can be followed by active sleep (stage 4) and then go back to stage 2. As we can see from a diagram above, stage 2 takes almost a half of time among all sleep stages.