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The basic rest–activity cycle (BRAC) is a physiological arousal mechanism in humans proposed by Nathaniel Kleitman, [1] hypothesized to occur during both sleep and wakefulness. Empirically, it is an ultradian rhythm of approximately 90 minutes (80–120 minutes [ 2 ] ) characterized by different levels of excitement and rest.
Astronomy – Axial precession – CNO cycle – Eclipse cycle – Eclipse – Full moon cycle – Galactic year – Great Year – Lunar phase – Mesoamerican calendars – Metonic cycle – Milankovitch cycles – Mira – Moon – Nutation – Orbit – Orbital period – Saros cycle – Sothic cycle – Secularity – Sidereal year ...
The sleep cycle is an oscillation between the slow-wave and REM (paradoxical) phases of sleep. It is sometimes called the ultradian sleep cycle, sleep–dream cycle, or REM-NREM cycle, to distinguish it from the circadian alternation between sleep and wakefulness. In humans, this cycle takes 70 to 110 minutes (90 ± 20 minutes). [1]
A circadian rhythm (/ s ər ˈ k eɪ d i ə n /), or circadian cycle, is a natural oscillation that repeats roughly every 24 hours.Circadian rhythms can refer to any process that originates within an organism (i.e., endogenous) and responds to the environment (is entrained by the environment).
Dynastic cycle (traditional Chinese: 朝代循環; simplified Chinese: 朝代循环; pinyin: Cháodài Xúnhuán) is an important political theory in Chinese history. According to this theory, each dynasty of China rises to a political, cultural, and economic peak and then, because of moral corruption, declines, loses the Mandate of Heaven ...
The bunker experiment was a scientific experiment that began in 1966 to test whether humans, like other species, have an intrinsic circadian clock. [1] It was started by Jürgen Aschoff and Rütger Wever of the Max Planck Institute for Behavioral Physiology and later taken over by Jürgen Zulley.
One of the important questions in sleep research is clearly defining the sleep state. This problem arises because sleep was traditionally defined as a state of consciousness and not as a physiological state, [14] [15] thus there was no clear definition of what minimum set of events constitute sleep and distinguish it from other states of partial or no consciousness.
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.