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[6] [4] Light seems to have therapeutic antidepressant effects when an organism is exposed to it at appropriate times during the circadian rhythm, regulating the sleep-wake cycle. [ 6 ] [ 4 ] In addition to mood, learning and memory become impaired when the circadian system shifts due to light stimuli, [ 6 ] [ 20 ] which can be seen in studies ...
Without the SCN, rhythms in body cells dampen over time, which may be due to lack of synchrony between cells. [37] Many SCN neurons are sensitive to light stimulation via the retina. [39] The photic response is likely linked to effects of light on circadian rhythms.
The pineal gland (also known as the pineal body [1] or epiphysis cerebri) is a small endocrine gland in the brain of most vertebrates. It produces melatonin, a serotonin-derived hormone, which modulates sleep patterns following the diurnal cycles. [2] The shape of the gland resembles a pine cone, which gives it its name. [3]
Motivated by the possibility that a substance from the pineal gland could be beneficial in treating skin diseases, they extracted and identified melatonin from bovine pineal gland extracts. [64] Subsequent research in the mid-1970s by Lynch and others demonstrated that melatonin production follows a circadian rhythm in human pineal glands. [65]
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.
Summary of pervasive effects of light. 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 ...
The amount of blue light received by ipRGCs regulates the circadian rhythm to control cycles of alertness [20] and sleepiness. The more light stimulation, the less signals are transmitted to the pineal gland through the SCN of the hypothalamus [21] to produce melatonin. Blue light exposure, particularly in the evening or at night, suppresses ...
In the early 1980s, Takahashi and Menaker studied the bird pineal gland culture system in vitro to understand circadian oscillations, and they demonstrated that the suprachiasmatic nucleus (SCN) of the hypothalamus, [9] which had been identified as the control center for circadian rhythms in mammals, played the same role in birds. [10]