The circadian clock system in the retina allows the anticipation of the normal cycle of photopic and scotopic visual conditions that alternate with the cycling of solar day and night. The retinal circadian clock drives many processes within the retina including gene expression, synaptic communication and metabolism, which reconfigure retinal circuits and shape the functioning of the retina according to time of day. This circadian clock is responsible for the temporal organization of a wide variety of functions, ranging from sleep and food intake, to physiological measures such as body temperature, heart rate and hormone release.Įxperimental evidence has shown that the mammalian retina contains a complete circadian clock system –biochemical machinery that generates temperature-compensated 24 hour oscillations, an input pathway by which light synchronizes the cycling of the retinal clock to the environmental light/dark cycle, and neurochemical output pathways that transmit the clock’s influence throughout the retina and into the rest of the brain. In mammals, including humans, the master pacemaker controlling 24-hour rhythms is localized in the suprachiasmatic nuclei of the hypothalamus (SCN).
Generally, these rhythms are not just passive consequences of cyclic fluctuations in the environment, but instead originate within the organism. Daily rhythms are a common feature of living systems.
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