The word circadian comes from a Latin
phrase meaning "about a day". Circadian
rhythms thus are physiological and behavioural characteristics
that follow a daily pattern. Our circadian rhythms
are controlled by a "biological clock" in
the brain, which consists of a tiny clump of cells
known as the suprachiasmatic nucleus. These cells
are greatly influenced by the daily change between
sunlight and darkness, with sunlight promoting wakefulness
and darkness setting the body for sleep.
Circadian rhythm disorder is a persistent or recurrent
pattern of sleep disruption leading to excessive sleepiness
or insomnia because of a mismatch between the sleep-wake
schedule required by a person's environment and his
or her circadian sleep-wake pattern. The interruptions
in sleep causes significant distress or impairment
in social, occupational, etc. The disturbances does
not occur exclusively during the course of another
sleep disorder, and is not due to the direct physiology
effects of drugs or a general medical condition.
Foreword
