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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).
Neurons in an intact SCN show coordinated circadian rhythms in electrical activity. [23] Neurons isolated from the SCN have been shown to produce and sustain circadian rhythms in vitro, [24] suggesting that each individual neuron of the SCN can function as an independent circadian oscillator at the cellular level. [25]
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.
Any biological process in the body that repeats itself over a period of approximately 24 hours and maintains this rhythm in the absence of external stimuli is considered a circadian rhythm. [4] It is believed that the brain's suprachiasmatic nucleus (SCN), or internal pacemaker, is responsible for regulating the body's biological rhythms ...
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 ...
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]
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The SCN of the hypothalamus contains an endogenous pacemaker that regulates circadian rhythms. [4] The zeitgeber found to have the most profound effect on the SCN is light, which is the form of stimulation of which conversion is needed for it to be processed by the brain. Neurotransmitters that travel the RHT are responsible for delivering this ...