»Sleep and Circadian Rhythms
~ Circadian rhythms are regular changes in mental and physical characteristics that occur in the course of a day
~ circadian is Latin for "around a day"
~ most circadian rhythms are controlled by the body’s biological "clock."
~ this clock, called the suprachiasmatic nucleus or SCN, is actually a pair of pinhead-sized brain structures
~ that together contain about 20,000 neurons
~ the SCN rests in a part of the brain called the hypothalamus, just above the point where the optic nerves cross
~ light that reaches photoreceptors in the retina (a tissue at the back of the eye) creates signals
~ that travel along the optic nerve to the SCN
~ signals from the SCN travel to several brain regions, including the pineal gland,
~ which responds to light-induced signals by switching off production of the hormone melatonin
~ the body’s level of melatonin normally increases after darkness falls, making people feel drowsy
~ the SCN also governs functions that are synchronized with the sleep/wake cycle,
~ including body temperature, hormone secretion, urine production, and changes in blood pressure

»Circadian rhythm

Clockwork Genes: Biological Rhythms in Health and Agriculture
~ by Steve A. Kay, Dean and Richard A.Atkinson Professor of Biological Sciences at UC San Diego.
~ pants, animals and humans have developed highly accurate daily clocks, called circadian rhythms
~ to control behavior and metabolism
~ in people, these clocks control such things as our sleep-wake cycles, blood pressure, fat metabolism, and cognitive functions
~ in some animals, these clocks affect a wide range of behaviors, from courtship to pollination
~ plants use their clocks to know when to flower
~ Kay explored how these clocks are constructed, how they differ among organisms, and
~ how they may eventually be manipulated to benefit health and agriculture

»Circadian Rhythms
~ all eukaryotes and some microbes e.g., cyanobacteria display changes in gene activity, biochemistry, physiology, and behavior that wax and wane through the cycle of days and nights

»Journal of Circadian Rhythms