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SCN Core and Shell

Meaning

The suprachiasmatic nucleus, or SCN, is the primary circadian pacemaker in mammals, responsible for orchestrating daily biological rhythms. It comprises two functionally distinct regions: the core and the shell. The core region receives direct photic input from the retina, acting as the primary synchronizer of the SCN to the external light-dark cycle. The shell region integrates non-photic inputs and translates the core’s rhythmic signals into outputs that regulate downstream physiological processes.