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How many stages of sleep are there?

Practically everyone has heard about the different phases of the dream, however, very few know exactly what they are. Next, we will explain how many sleep stages are there and what each of them consists of.

Before starting, it is very important to distinguish between two types of stages. The so-called Non-REM sleep, composed of long and slow wave sleep cycles; and REM (Rapid Eye Movement) sleep, formed by short wave cycles and paradoxical sleep.

How are the different stages of the sleep analyzed or studied? Well, to carry out a reliable study of the stage of a person’s sleep, several instruments are needed. An electroencephalogram (EEG), to record brain activity; the electromyogram (EMG), to make a record of the electrical activity produced by the skeletal muscles; and the electrooculogram (EOG), to measure the activity and movement of the eyes. These instruments are responsible for making records of electrophysiological parameters.

Stages or phases of sleep

The stages of sleep, also known as sleep cycles, as we mentioned are composed of non-REM sleep and REM sleep. In one night, an individual can experience between 4 and 6 complete sleep cycles. Each cycle is composed of a total of 5 stages of sleep. So, here we have the first answer to your questions. How many stages of the dream are there? A total of 5 stages, which we will see in greater depth below.

Non-REM stages

The non-REM sleep represents approximately between 75 and 80% of total sleep consists of four stages of sleep. It is characterized by its long and slow wave cycles, which indicates a low electrical activity in the central nervous system.

Stage 1: Numbness

It is a state of drowsiness, with periods of vigilance and light sleep. This stage represents approximately between 5 and 10% of our total sleep. In this stage of the sleep we are most exposed to awaken by low intensity noises. Alpha waves and theta waves begin to appear.

It should be noted that not only does this stage appear when we are falling asleep, but it also appears in the different sleep cycles throughout the night. In this period of the dream hallucinations can occur, both in the entrance and in the exit of this stage.

Stage 2: Light sleep

This is the most frequent stage of the sleep cycle and represents about 50% of total sleep. During light sleep, physiological and muscular activity decreases considerably. Little by little we will be disconnecting from our surroundings and we will go more and more into a deeper sleep. The EEG record shows periods of theta activity, sleep spindles (12-14 Hz) and K complexes (acute waves that help the subject does not wake up).

You may have on many occasions dreamed that you fell off a cliff and you have woken up at once. That feeling many of us experience has a clear scientific basis that we will explain below.

In some occasions, during this stage of light sleep, our pulsations are very low and the sleep is deep enough making it difficult for the brain to establish a connection with our body. This causes the brain to send a sudden impulse to corroborate that everything continues to function normally. The impulse produces a pronounced reaction from the body, usually a rapid movement of the body or hypnic jerk.

Phase 3 and 4: transition phase and delta sleep or deep sleep

Deep sleep is the stage where our body rests most. Image source: Pixabay

Although in the model of Dement and Kleitam, deep sleep is composed of the 3rd and 4th stage, the truth is that today, we usually refer to both these stages together.

Stage 3 is what we know as the transition phase. It represents between 3 and 8% of the total sleep. Its approximate duration is 2-3 minutes and during that period, our body prepares for deep sleep, predominating delta waves and decreasing, even more, the physiological activity.

On Stage 4, known as delta dream or deep sleep, the brain waves wide and slow. Our heart rate decreases considerably and during this sleep it is the hardest to wake up. It occupies between 15 and 20% of total sleep and considered the optimal stage for resting our body. In fact, this phase will determine the good or bad quality of our sleep.

Phase 5: REM or rapid eye movement sleep

We reach the last phase of sleep, known as REM sleep, where most of the physiological activity happens. Our muscle tone is diminished considerably and we start our dreams.

We also know the REM stage as a paradoxical dream. It is believed that REM sleep is fundamental for the development of our brain  and the consolidation of memories. REM sleep represents about 20% of total sleep, and is proportionately greater in children.

As we have said before, during the sleep period, we will repeat between 4 and 6 sleep cycles, going through each and every one of the previously mentioned phases on several occasions. The stages of the sleep are one of the great mysteries of our brain and, although science has already offered answers to many of the questions we ask ourselves, we still have much to discover. And when that happens, you will read it here at ScienceBinge.

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