Stages of Sleep
What are the two stages of sleep?
1) NREM 2) REM Each sleep cycle (consisting of REM & NREM sleep) lasts 90-100 minutes, there are 4-5 cycles a night.
What is REM paralysis?
During REM paralysis, the body is totally relaxed. Most of the skeletal muscles are limp, thus during a night dream, the sleep can't act out their dream and harm themselves or someone else.
What is the fourth stage of NREM?
It is our deepest sleep, from which we are very difficult to wake. If woken, the sleeper takes up to 10 minutes to orient themselves (sleep inertia). In cycles close to morning there may be no stage 3 or 4 sleep. During stage 3 & 4, night terrors may occur. These are more terrifying than a nightmare. Very little dreaming occurs, though occasionally there are bizarre/disjointed dreams. Stages 3 & 4 NREM sleep play a key role in physical recovery from exertion.
What is the third stage of NREM?
It is the start of the deepest period of sleep. Our metabolic rate, heart rate and body temperature are reduced even further than during a light sleep. There is a decrease in brain activity. Sleep walking most commonly occurs during stages 3 & 4 of NREM. Sleep talking can also occur.
What is the first stage of NREM?
It occurs when we first go to sleep. We lose awareness of ourselves & our surroundings but are still aware of faint sounds in the environment. We drift into a light sleep from which we can be easily woken. It is common to experience the hypnic jerk - a spasm of part of the body). This stage of NREM lasts for 5-10 minutes per cycle.
What is REM sleep?
REM sleep is called the paradoxical sleep, because internally the brain is active, but externally the body appears calm and inactive i.e we experience REM paralysis. Most of our dreaming occurs during REM; 80% of subjects report having dreams if woken. Nightmares occur during REM sleep, as the brain is highly active and dealing with symbolic content in a person's life that may be causing psychological disturbance at either a conscious or unconscious level. About 20% of adult sleep is REM, for newborn babies it is about 50% due to the rapid brain development which occurs during this early part of life.
What is the second stage of NREM?
Researches say that stage 2 is when we are first truly asleep, but it is still a light sleep - we are easily woken during this stage. We spend more time in stage 2 than in any other stage.
What is the NREM stage?
The transition period from being awake to being asleep is known as the hypnogogic stage, characterised by slow rolling eye movements. Some people report floating-like feelings or a sudden jerk - even images flashing briefly in our mind. This stage only lasts 1-2 minutes prior to entering stage 1 of NREM.
Define sleep.
We are considered 'asleep' when we get to the point where there is a loss of awareness of our internal state (we can't feel pain, warm, cold, fatigue) and external surroundings (no longer noticing smells, sounds etc)
What is the duration of REM sleep?
When REM sleep occurs, it takes 1.5 hours to have your first REM dream, then another 1.5 hours for the second REM dream, etc. The duration of each REM cycle increases with each cycle & they occur closer together (except the last stage of sleep). Early in the night, REM may last a few minutes - later (during the fourth or fifth sleep cycle) it can last up to an hour.
