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Sleep
a reversible behavioural state of perceptual disengagement from and unresponsiveness to the environment.
Reversible → sleeper can always be woken up with a strong enough stimulus
Perceptual disengagement → no awareness of sights, sounds, smells and other sensory stimuli
Unresponsive – sleeper not responsive to external environment
Sleep is a psychological construct
a concept that is ‘constructed’ (created/made) to describe specific ‘psychological’ activity (thoughts/feelings/behaviour), or a pattern of activity, that is BELIEVED to occur or exist but cannot be directly observed.
Biological rhythms
refer to naturally occurring patterns of cyclic changes in bodily functions or activities that repeat themselves through time in the same order.
body temperature
blood pressure
sleep-wake cycle
secretion of certain hormones
3 TYPES
Circadian rhythms, Ultradian rhythms, Infradian rhythms
Circadian Rhythm
cycle with a duration of approximately 24 hours e.g. sleep-wake cycle
Suprachiasmatic nucleus (SCN) small part in hypothalamus → regulates the timing and activity of sleep-wake cycle & other circadian rhythms
SCN - has a pair of pinhead sized structures containing 20,000 neurons
Circadian Rhythm - The Sleep-Wake Cycle
SCN receives info about amount of incoming light from eyes → adjusts sleep-wake cycle accordingly
light is the MAIN environmental cue that influences the cycle
→ sends neuronal messages to pineal gland to produce less or more melatonin hormone (LESS light = MORE melatonin, MORE light = LESS melatonin)
Melatonin
Higher melatonin levels = greater drowsiness
Lower melatonin levels = greater alertness
only comes out at night → from PINEAL GLAND
artificial lighting can be bright enough to impede the release of melatonin.
synthetic melatonin is sometimes prescribed to treat some types of sleep disorders.
Ultradian rhythms
cycle that is shorter than 24 hours e.g. REM/NREM cycle
Infradian rhythms
cycle that is longer than 24 hours e.g. menstrual cycle