The sleep during the night is organized by cycles. Every cycle includes a phase of Slow Sleep (SL), followed by a phase of REM sleep (POSTAL AREA). Then the state of awakening comes.

Circadian organization of the states of attentiveness at the man

- The Slow Sleep is cut in degrees which are classified in order of growing endormissement, of I in IV. For stages III and IV, we speak about deep SL.

The activity of the brain is characterized by more and more slow waves of the stage I at the stage IV, and a high voltage. The muscular tonus decreases in the stage(stadium) I at the stage IV. The eye movements are at first slow (stage I), then tend to disappear.

- During the REM sleep, the activity of the brain is fast and of low voltage. The muscular tonus is similar to that of the phase of awakening, and this electric activity contrasting with the state of sleep is at the origin of the naming "REM sleep", the muscular tonus is abolished and becomes again important from the alarm clock. The eye activity is intense.

The first phase of POSTAL AREA appears on average one hour and a half after the endormissement; she follows upon the various stages of SL.

On average, at the adult, the number of cycles varies from 4 to 6 and the duration of every cycle borders 90 minutes, but the variations can be very important from an individual to the other one.

At the young adult, the SL represents 80 % of the total duration of the sleep.
Variations of the states of attentiveness Numerous factors are taken into account:

.L’ age

- At the infant, the Time of Total Sleep is superior to that of the adult and the POSTAL AREA represents 60 %. - At the child, the POSTAL AREA decreases quickly between 1 and 15 years, as well as the time of total sleep. - At the adult, the POSTAL AREA decreases very slowly at the same time as the increase of the age. - At the old persons, the schedules of sleep tend to advance (a bedtime earlier, to raise earlier). The sleep becomes unstable. The quantity of SL in stage IV decreases, sometimes in a considerable way.

Other

- According to the individuals, the differences are very important
- According to the environment (sound level)

The confusions of the sleep and the attentiveness at the adult

Hyposomnies and sleeplessness
The sleeplessness groups together all the complaints concerning the duration and\or the quality of the sleep.
We distinguish three types of sleeplessness:

- The sleeplessness of endormissement meet at the anxious or overstrung subjects.
- The sleeplessness of the night environment are characterized by night-alarm clocks and difficulties falling asleep again.
- The sleeplessness of the night end correspond to a premature alarm clock and can be the sign of a depression.

The causes of sleeplessness are multiple:

- The coincidental sleeplessness can be linked to a well determined cause.
- The chronic sleeplessness can be due to factors psychophysiologiques, psychiatric factors (depression), organic factors (disease of Parkinson, disturb endocriniens, apnées of the sleep), or still factors iatrogènes (weaning of certain drugs some barbiturates, benzodiazépines, cocaine; grip of alcohol or certain medicines as corticoids...

Hypersomnies
She can be physiological (qualified persons of « big sleepers »), idiopathique, characterized by a total time of sleep superior at 3 pm and one or several long phases of diurnal sleep.

The narcolepsie is a dysomnie: it is about a bad distribution of the states of attentiveness during 24 hours(12 pm), Time of sleep and duration of the POSTAL AREA being generally normal. She is characterized by uncontrollable accesses of sleep during day, activated by the stress or the emotion...

Endormissements is directly made in POSTAL AREA. We observe frequently falls of muscular tonus.