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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.
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).
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.
Steppe eagles are diurnal, and hunt during the day. Humans are diurnal, and organize their work and business mainly in the day. [a] Diurnality is a form of plant and animal behavior characterized by activity during daytime, with a period of sleeping or other inactivity at night. The common adjective used for daytime activity is "diurnal". The ...
The activity/rest cycle (sleep) in animals is one of the circadian rhythms that normally are entrained by environmental cues. In mammals, such endogenous rhythms are generated by the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. Entrainment is accomplished by altering the concentration of clock components through altered gene ...
Many college students have variable day-to-day class schedules that change one's daily routine. Additionally, many college campuses offer late night social activities that can begin as late as 10 pm. These activities are crucial for college students because they allow socialization and bonding with one another, which may boost one's mood.
In schedules involving night shifts and fragmentation of duty periods through the entire day, a sort of polyphasic sleeping schedule was studied. Subjects were to perform two hours of activity followed by four hours of rest (sleep allowed), this was repeated four times throughout the 24-hour day.
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] Within the sleep of adults and infants there are cyclic fluctuations between quiet and active sleep.