The human internal body clock in healthy and disrupted sleep

The human circadian system, regulated by the suprachiasmatic nuclei, establishes normal sleep and wake phases.

• The suprachiasmatic nuclei (SCN) act as the biological clock, coordinating the body's rhythmic functions.
• Light exposure is crucial for resetting the intrinsic circadian cycle, which is slightly longer than 24 hours.
• Disorders in the circadian system are frequently associated with sleep abnormalities, including circadian rhythm sleep disorders.
• Conditions like jet lag syndrome and shift work sleep disorder are directly linked to dysfunctions in the circadian system.
• Other sleep disorders, such as insomnia, could also be related to abnormalities in the circadian system.

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