> Within the sleep cycle an example of ultradian rhythms exist - the five stages of sleep.
> The first four stages of sleep are called NREM sleep (non-rapid eye movement).
> The fifth stage of sleep are called REM sleep, so called because of the accompanying movements of the eye beneath the closed eyelids.
> One sleep cycle goes through all five stages and lasts about ninety minutes.
> The awake brain produces a typical pattern called a beta wave.
> Stages 1 & 2 = light sleep, characterised by a change in electrical activity of the brain - as you become more relaxed your brain waves become slower (alpha) & as you go to sleep they become even slower (theta) - heart rate slows & temperature drops.
> Stages 3 & 4 = characterised by even slower delta waves (slow wave sleep) - very hard to wake someone up, although person isn't unconscious…