Sleep stages

The stages of sleep are studied using various instruments such as the electroencephalogram (EEG), the electromyogram (EMG) and the electrooculogram (EOG) that record electrophysiological parameters. Likewise, parameters such as heart rate, respiratory rate and electrical conductance of the skin are collected. Sleep is made up of long wave sleep cycles, short wave sleep (both of which make up the so-called Non-REM sleep) and paradoxical sleep or si-REM sleep. The cycles of short waves and paradoxical or si-REM sleep alternate with each other and last about 45 minutes. In one night between 4 and 6 of these cycles can occur.

Stages

During the period in which we rest, sleep goes through different phases:

• Dream not REM: 1-4
  • Slow-wave dream: 3-4 phases

• Stage 1 (Adormecimiento/Vertex Acute Waves): It is a state of drowsiness that lasts about ten minutes, where the EEG shows a certain theta wave activity (3,5-7,5 Hz). It is the transition between vigilance and sleep. They can give hallucinations both at the entrance and at the exit of this phase. This stage occupies 10% of the total sleep time.

• Stage 2 (Light Dream): Both heart rate and respiratory decrease. EEG registration shows periods of theta activity, sleep bones and K complexes. Sleep bones are wavesets between 12 and 14 Hz that happen several times per minute between phases 1 and 4 of sleep. The K complexes are acute waves that appear abruptly and act as an inhibition mechanism so that the subject does not wake up. Thus, we suffered variations in brain traffic, periods of calm and sudden activity, which makes it harder to wake up. In some cases, we arrive at a process in which our pulsations are extremely low and sleep is so deep that the brain presents difficulties in registering contact with the body, so it sends an impulse to corroborate that such connection between the brain and the body is in normal operation. This impulse produces a reaction, which is abruptly recreated by the mind, so there is a violent feeling and the body acts on the basis of that feeling, usually with a violent and rapid movement of the body. The latter is popularly known as "To dream that we fall." (50 % of time).

In it sporadically arise two typical graphoelements of sleep EEG: sleep spikes (sharp waves) and K complexes (sudden spikes).

• Stage 3: Transition phase to deep sleep. We spend about 2-3 minutes at this stage.

• Stage 4 (Delta Dream): Slow sleep phase, brain waves at this stage are wide and slow as well as breathing rhythm. It's hard to wake us up being at this stage, which lasts about 20 minutes. They don't usually dream. It occupies 20% of total sleep time. The dream of slow waves is the reconstructive phase of sleep, essential to help the mind and body recover and rebuild after each day. Growth hormones are secreted to facilitate muscle healing, as well as to repair tissue damage.

• Phase REM: a phase in which the brain is very active, the brain stem blocks the neurons in a way that we cannot move. REM comes from the English phrase Rapid Eye Movement (Quick Moving of the Eye), due to the characteristic movement of eyeballs under the eyelids. This is the phase where we dream and capture a lot of information from our environment due to the high brain activity we have. This phase shows a brain activity similar to that of the vigil.

Throughout the night, slow (NREM) sleep alternates with paradoxical (REM) sleep. The total of the paradoxical dream is 25% of the dream.

Sleep disorders are classified into dyssomnias, parasomnias, sleep disorders related to medical or psychiatric causes and other sleep disorders, which affect the different phases of sleep in a more or less accentuated way. Likewise, some drugs used for the treatment of sleep disorders can modify the architecture of sleep, so they must be administered under strict medical supervision, with the doctor being the one who must assess the cost/benefit ratio of their administration in a personalized way., and never the patient.