THE PHYSIOLOGY OF SLEEP AND ITS STAGES - NEUROPSYCHOLOGY - 2024

The physiology of sleep is characterized by two phases, REM and nonREM and REM in four stages. Adults normally get about 8 hours of sleep a day; If the 8 hours are carried out continuously, about 4 or 5 cycles will be carried out. Each cycle can be understood as complete phases of sleep (from stage I to REM), and can last between 90 and 120 minutes each.

When we speak of sleep or the process of sleeping, we refer to a physiological and natural state in which the level of alertness and vigilance is diminished, since the person is resting.

And although it seems that the external stillness of the subject, internally makes it in a state of tranquility, it is something totally wrong, because internally the body of the person who sleeps does not stop and continues to function as complexly as when we are awake.

Sleep is composed of different degrees of intensity or depth, where in turn there are modifications of the organism that accompany each phase or stage of sleep.

Basic theories about sleep

One of the first theories formulated to understand the sleep process was the passive sleep theory, which Bremmer formulated in 1935. This theory was based on the fact that the excitatory areas of the brainstem were depleted throughout the day, so by the time it was time to sleep, they were already fatigued and turned off.

It would be something similar to the battery of your mobile, taking the fact of charging it as our sleep process.

But after several years and some experiments, the theory became obsolete and a different vision began to be taken. Currently the theory that accompanies this process says that sleep is produced by active inhibition.

This means that there is a small area in the brain that causes parts of it to turn off during sleep. Something like a watchdog that prevents other brain areas from doing their job while you sleep.

But you have to be clear that the brain does not sleep while you do it, but that its way of working changes to be in line with the process.

To this day, it is not yet known what is the physiological purpose that creates the need for any living being to sleep. As you read above, sleep is considered a priority need, and even the fact of not sleeping for a while can cause disorders and even death although it sounds incredible.

People cannot go without sleep at all for 1 to 2 nights. From the third night without sleep, disorders would appear that little by little would increase in severity and would have serious consequences. This would affect areas such as attention, memory, mood and even hallucinations and seizures may appear.

Stages of sleep

There are 4 phases of the dream process of Non REM sleep (NREM) and one of REM sleep.

-NREM phase

This stage is also known as non-Rem, it comes from the English translation of "non-rapid eye movement", this first stage is the first contact with sleep.

It is the first dream state that we enter and for most adults it will be the place that occupies 75% of their entire dream.

The NRem stage is divided into 4 phases, in which the characteristics of sleep are shaped, they are as follows:

NREM Stage- Phase1

It is the stage where we feel drowsy or are sleepy. The waking state is disappearing since the Alpha rhythm also does. At the moment the muscle tone is not completely relaxed. The Beta waves have disappeared.

NREM Stage- Phase II-III

It is the stage where although we are asleep, the sleep is light, the Alpha rhythm disappears more and more, there is still muscle tone. We gradually experience the entrance to theta waves.

NREM Stage- Stage IV

This is the stage of deep sleep, the encephalographic rhythm is very low, the muscle tone is maintained or may be very diminished. Delta waves appear in our brain.

Actually, these stages differ in that the muscular atony increases little by little and the brain waves little by little change depending on the relaxation of the body.

-REM phase

It is the paradoxical sleep phase, since during this phase the brain has an activity that is reminiscent of that which occurs when we are awake. Also during this phase rapid eye movements are appreciated. The body is atony.

What we dream about occurs during this phase. To date, there is no clear theory as to why eye movement occurs during REM phase.

How is sleep organized at night?

Adults normally get about 8 hours of sleep a day. If the 8 hours are performed in a row, about 4 or 5 cycles will be performed. Each cycle can be understood as complete phases of sleep (from stage I to REM), and can last between 90 and 120 minutes each.

The distribution is normally as follows:

• Phase I during the cycle would be developing approximately 1.5% of the total cycle. This means that if the cycle lasts 100 minutes, only 1 minute and a half the body would be in phase I.
• Phase II during the cycle would be present approximately 25% of the total cycle. In a cycle of 100 minutes, 25 minutes would be the duration of phase II.
• Phases III and IV during the cycle would last 45% of the total cycle. In a 100 minute cycle, these phases would last approximately 45 minutes.
• The REM phase, during the cycle, would last 25% of the total cycle. So in a cycle of 100 minutes, only 25 minutes correspond to the paradoxical dream and dreams.

How much do people sleep?

The distribution of sleep throughout the day is different depending on various factors such as age, daily activity, health, etc.

Babies sleep most of the time, although as the child grows, the waking states are more and more prolonged. It is curious to know that babies have a higher percentage of REM sleep than adults, and it is throughout childhood when that percentage will begin to decrease to reach a normalized percentage.

In adults, the need for sleep is less than in infants. An adult can sleep between 5 and 9 hours and have a good performance throughout the day. Although it is always advisable to sleep between 7 or 8 hours a day to have good health and quality of life.

Different times of life and vital situations can reduce the amount of sleep. For example, when we go through times where we have a lot of intellectual activity, we will have more need to sleep than at times when stress is very present in our lives.

Older people have a lower need for sleep and their rest periods are shorter. They usually wake up during the night and the percentage of stage IV sleep. However, the REM phase seems invariable throughout life in terms of its duration in the sleep cycle.

Sleep is governed by a biological clock

The sleep process is governed by a biological rhythm understood as the circadian rhythm. These are 24-hour cycles that are related to day and night.

The circadian rhythm of sleep and wakefulness is approximately every 25 hours. This data is curious because it tells us that we are programmed in such a way that we allow ourselves to be influenced by a certain rhythm or cycle.

In our central nervous system there is one of our biological clocks. This watch makes non-REM sleep and REM sleep last for a set time.

Circadian rhythms depend on the body's interaction with stimuli that come from outside. Of these external stimuli, the most important and the one that most influences us is the light, as well as the time to wake up, since this time can be set strictly.

The time we go to sleep is also important, and although we can set some routine guidelines that make us go to bed at a certain time, normally we cannot decide the exact moment in which we fall asleep.

If the person is totally isolated from these stimuli, that is, they do not perceive changes in light, temperature or activities, they would also follow a normal biological sleep rhythm, since the human body is programmed to follow the rhythm we need without the need for external influences.

Dreams

When we dream, our brain does not rest like we do, because brain activity continues in constant and active movement. Also while we sleep we have some curious experiences, called dreamlike or more commonly known as dreams.

As you read above, dreams occur during the REM phase (hence many experts think that eye movement occurs as a result of those dreams) and they are in color and moving, as if we were watching a movie.

During the deep sleep phase, you sometimes dream too. The only difference is that those dreams are of a more abstract kind.

During REM sleep, our brain activates the reticular system, which is related to the brain and forebrain. These structures are also activated when we are awake.

These structures are involved in sensory stimulation, so being activated explains why when we dream we have the feeling of actually living that dream. We can even feel what we dream of.

In addition, during sleep the limbic system is also active, with structures such as the amygdala, and the cngular cortex. This system is in charge of emotional life, so this can also give a rational explanation of why during sleep we not only sensually feel what we are dreaming, but we also feel it emotionally.

During sleep, the prefrontal cortex, which is responsible for mental reasoning, is inhibited, so this can give us relevant information about the little logic that our dreams often have.

I hope this article has given you information that you did not know about the natural process of sleeping that you do every night.

6 curiosities about sleep

The blind also dream

Those who were born blind can dream just like people who can see. The difference is that the dreams of the blind are represented by other senses such as sound and smell.

Women dream of sex the same amount that men do

Women dream of sex just like men do. In equal conditions both in quantity and frequency. Maybe the difference is only in the content.

Not everyone dreams in color

12% of people dream in black and white. This data is curious, because it is said that since television appeared, people previously dreamed in black and white and it was after the appearance of the device that we began to dream in color.

Animals dream too

Surely if you have a pet, sometime while sleeping you have observed that it moved as if it were doing something. Animals like us humans also have dreams in fact while they dream, they have the same type of brain waves as us.

Your body reacts to your dreams as if they were a real experience

The experience we live during the moment in which we dream is recorded as if it were a real experience, the difference is that you truly know that it was a dream, but it is difficult for your brain to assimilate and process it that way..

We only dream of the faces we already know

Your brain does not invent faces when dreaming. When we dream of people, the faces that these show are the faces of real people that we have ever seen during our life. We may not remember the face or we may not know the person, but it is certainly part of a memory.