Sleep
Sleep stages
Sleep is divided into two distinct states called rapid eye movement (REM) and non-rapid eye movement (NREM). NREM is subdivided into four stages.
It takes the average person 15-20 minutes to fall asleep, this is called sleep latency (characterised by the onset of stage I sleep). Once asleep one descends through stages I-II and then III-IV (deep stages). After about 90 minutes of sleep one enters REM. The rest of the sleep comprises of cycles through the stages. As the sleep progresses the periods of REM become greater and the periods of NREM become less. During an average night's sleep one spends 25% of the sleep in REM and 75% in NREM.
REM sleep has certain characteristics that separate it from NREM
Sleep is divided into two distinct states called rapid eye movement (REM) and non-rapid eye movement (NREM). NREM is subdivided into four stages.
| Sleep stage | % of time spent in stage | EEG findings |
|---|---|---|
| I | 5% | Theta waves |
| II | 45% | K complexes and sleep spindles |
| III | 12% | <50% Delta waves |
| IV | 13% | >50% Delta waves |
It takes the average person 15-20 minutes to fall asleep, this is called sleep latency (characterised by the onset of stage I sleep). Once asleep one descends through stages I-II and then III-IV (deep stages). After about 90 minutes of sleep one enters REM. The rest of the sleep comprises of cycles through the stages. As the sleep progresses the periods of REM become greater and the periods of NREM become less. During an average night's sleep one spends 25% of the sleep in REM and 75% in NREM.
REM sleep has certain characteristics that separate it from NREM
| Characteristics of REM sleep |
|---|
| - Autonomic instability (variability in heart rate, respiratory rate, and BP) - Loss of muscle tone - Dreaming - Rapid eye movements - Penile erection - Deafness |
