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Psychology Mrs Heywood
Outline and Evaluate the Stages and Cycles of Sleep.
There are five stages of sleep that form a sleep cycle. Studies have shown that most people
experience, and ideally complete, five complete cycles each night with each lasting from between
Stage 1 is characterised by the appearance of theta brain waves, slowed eye and muscle activity,
a brain activity decrease of 50% and sudden muscle contractions also known as `hypnogogic states'.
These are consciously defined as the feeling of falling followed by the reflexive defence jerk which
disrupts the cycle.
Stage 2 is shown by the continuation of theta waves, but with the appearance of `sleep spindles'
and `K-Complexes'. These are wave phenomena; a `sleep spindle' may represent periods in which
the brain is trying to restrain high-order processing in order to maintain a state of tranquillity. A
`K-Complex' consists of a high-voltage energy burst; often exceeding 100 µV. K-Complexes suppress
cortical arousal to external stimuli deemed non-threatening and also aid sleep-based memory
Stage 3 is defined as the true beginning of deep sleep. Very slow delta waves start to be
produced and no eye or muscle movement is noticed. It is very difficult to wake the sleeper at this
Stage 4 is the second-deepest stage of sleep. Delta waves are the only ones produced and no
eye or muscle movement is noted. Disorientation may be observed in the sleeper if awakened.
Finally, REM sleep is defined as having been entered at the advent of dreaming. Heart and
breathing rates are accelerated as is blood pressure. Breathing becomes shallow as the eyes begin
rapid and irregular movements. The muscles of the chin, neck, torso and limbs are paralysed. A failure
in this paralysis can result in somnambulism, or `sleep walking/talking'. Neuroactivity resembles
waking activity during REM sleep (which is why this is sometimes referred to as paradoxical sleep).
Sleeping is an ultradian rhythm, in that it occurs more than once every 24 hours. The stages are
monitored through EEGs (scalp electrodes), EOGs (eye electrodes) and EMGs (muscle electrodes).
These are scientific lab equipment which makes them highly reliable and less subject to bias because
of the objective nature of the method, but with a dip in ecological validity due to the fact that lab
conditions and electrodes are not found in natural sleep. Also, the sleep lab is an artificial
environment, and also has reductionist factors as it ignores effects that can be found outside of the
lab. It lacks mundane realism and the ecological validity that is found in the self-report method.
However, this is open to bias from the individual and also distortion. There is a pre-sleep period in
which it is impossible to recall. No study method can account for individual differences. Everyone
sleeps differently, regardless of age, gender or temperament etc.