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Although circadian rhythms are endogenous, they are adjusted to the local environment by external cues called zeitgebers (from German Zeitgeber (German: [ˈtsaɪtˌɡeːbɐ]; lit. ' time giver ')), which include light, temperature and redox cycles. In clinical settings, an abnormal circadian rhythm in humans is known as a circadian rhythm sleep ...
A circadian rhythm is an entrainable, endogenous, biological activity that has a period of roughly twenty-four hours. This internal time-keeping mechanism is centralized in the suprachiasmatic nucleus (SCN) of humans, and allows for the internal physiological mechanisms underlying sleep and alertness to become synchronized to external environmental cues, like the light-dark cycle. [4]
The sleep diary, or sleep log, is a tool used by doctors and patients. [1] [2] [3] It is a useful resource in the diagnosis and treatment of especially circadian rhythm sleep disorders, and in monitoring whether treatment of those and other sleep disorders is successful. Sleep diaries may be used in conjunction with actigraphy.
Because circadian clocks synchronize human sleep-wake cycles to coincide with periods of the day during which reward potential is highest – that is, during the daytime [16] – and recent studies have determined that daily rhythms in reward activation in humans are modulated by circadian clocks as well, [16] external influences on those ...
These variants occur near genes known to be important in photoreception and circadian rhythms. [37] The variant most strongly associated with chronotype occurs near RGS16, which is a regulator of G-protein signalling and has a known role in circadian rhythms. In mice, gene ablation of Rgs16 lengthens the circadian period of behavioural rhythm.
DSPD is a circadian rhythm sleep disorder, characterised by a mismatch between a person's internal biological clock and societal norms. [2] Chronotherapy uses the human phase response to light or melatonin. The American Academy of Sleep Medicine has recommended chronotherapy for the treatment of circadian rhythm and sleep disorders. [3]
In vertebrates, the master circadian clock is contained within the suprachiasmatic nucleus (SCN), a bilateral nerve cluster of about 20,000 neurons. [10] [11] The SCN itself is located in the hypothalamus, a small region of the brain situated directly above the optic chiasm, where it receives input from specialized photosensitive ganglion cells in the retina via the retinohypothalamic tract.
According to the International Classification of Sleep Disorders, Revised (ICSD-R, 2001), [10] the circadian rhythm sleep disorders share a common underlying chronophysiologic basis: The major feature of these disorders is a misalignment between the patient's sleep-wake pattern and the pattern that is desired or regarded as the societal norm...