The phases of sleep in adults each have a series of specific characteristics that we will see throughout this article.

The phases of sleep in adults can be studied using different instruments such as the electroencephalogram, the electromyogram and the electrooculogram. These devices record different electrophysiological parameters during the different phases of sleep.

In addition, they collect parameters such as heart rate, respiratory rate and electrical conductance of the skin. Before going directly into the subject of sleep phases in adults, it is important to have certain concepts clear in order to understand them.

What is the dream about?

As we already know, the phases of sleep in adults change while a person is asleep, however, do we know exactly what sleep is?

The dream is an active process generated by the discharge of specific neurons. In addition, it acts on most physiological and psychological processes and is in turn affected by them. This relationship makes sleep very important to our physical and mental health.

This process is regulated by the pineal gland, which is located at the base of the brain. This gland is responsible for synthesizing a chemical called melatonin, which is crucial for regulating sleep.

Both the synthesis and the release of melatonin are increased at night and decreased during the day. This is because these variations are responsible for controlling the circadian rhythm of sleep-wake, which adapts to the solar schedule.

Throughout life, sleep phases can vary, causing sleep to change both in quantity and quality. This variation will depend on:

  • Age of the person.
  • The state of health.
  • Physiological changes.
  • Others.

Phases of sleep in adults

During the hours of sleep, brain activity changes. These changes can be observed in the aforementioned instruments since depending on the phase of sleep in which the person is, it emits some electrical waves or others. In addition, two very well differentiated activities can be distinguished during sleep:

  • Rapid: or high-frequency activity: also called REM ( Rapid Eye Movements) phase characterized by rapid movements of the person’s eyes. It is also called a paradoxical dream. In this phase is when we dream of stories with a plot thread.
  • Slow activity or non-REM sleep: it is characterized by reflecting low-frequency waves in the EEG.

When a person is asleep, they suffer brief awakenings that are usually accompanied by physical movements when they go from the non-REM phase to the REM phase and vice versa.

On the other hand, the non-REM phase is in turn divided into 4 other phases with different characteristics between them. These phases alternate cyclically while a person is asleep. Approximately every 90-100 minutes, a new sleep cycle begins in which the last 20 or 30 minutes corresponds to the REM phase.

Phases of sleep in non-REM adults: phase I

It is characterized by a light sleep. People are still able to perceive most stimuli.

It is a little or no restful sleep in which the muscle tone decreases compared to when the person is awake.

Phases of sleep in non-REM adults: phase II

The nervous system blocks the pathways of sensory information, thus disconnecting itself from the environment and making it easier for the person to fall asleep. In this phase, sleep is partially restorative so it is not enough to fully rest. It occupies 50% of the sleep time in adults and also, eye movements disappear.

Phases of sleep in non-REM adults: phase III

It is a deeper sleep. In the case in which the individual woke up in this phase, he will feel confused and disoriented. In phase III you do not dream, since we have seen that you dream in the REM phase, but blood pressure and respiratory rate decrease significantly. In addition, the synthesis of growth hormone is increased. Phases of sleep in non-REM adults: phase IV

This last phase is the deepest phase of sleep. It is essential to recover both physically and psychically. Despite not being the typical phase of dreams, images can appear without any plot line. In addition, it is in this phase that certain sleep disturbances such as sleepwalking occur.

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