Psychology -> Stages of sleep one to four
Stages of sleep one to four
Stage one: This stage is characterised by small, irregular waves which are a combination of alpha and theta waves.
During this stage the individual is drowsy and is drifting off into a light sleep from which they can be easily awoken. The person's heart rate slows down and their muscles relax.
Apart from the very first time the person enters stage one sleep, this stage is known as REM sleep.
Stage two: In this stage sleep spindles begin to occur. These are sharply pointed waves recorded by the EEG. The EEG also shows rapid bursts of electrical activity with irregular brain waves.
Stage three: This stage is characterised by the onset of slower delta waves.These brain waves are high in amplitude and low in frequency. At this stage, the person becomes harder to awaken, their breathing and pulse rate slow down and their temperature drops.
Stage four: This stage consists of pure delta waves and it is extremely difficult to rouse the sleeper. This is the stage when sleep walking, sleep talking and night terrors occur.
Once the sleeper reaches stage four (about an hour after sleep begins) they then travel back up through stages three, two and one. When stage one is reached for the second time, REM sleep begins and the sleeper engages in about ten minutes of dreaming.
Most dreams occur during this REM stage. The EEG reveals brain wave patterns that are very similar to beta waves when a person is awake, active and alert. For this reason, REM sleep has been called 'paradoxical sleep'. It is also characterised by jerky movements of the eyes beneath the eyelids, hence the label, rapid eye movement. The person's heart rate also increases, their blood pressure rises and their breathing becomes faster and more irregular. Luckily for others, our muscles are paralysed, preventing us from acting out our dreams.
As the night progresses, the time spent in stages three and four decreases while REM sleep increases. The last stages or REM sleep can last up to one hour or so. The entire cycle of stages one through to four occurs approximately four to six times during an average eight hour period of sleep.