The body’s internal clock in health and disease

The master circadian rhythm in mammals is governed by the biological clock located in the suprachiasmatic nuclei of the hypothalamus.

• Multiple neuronal cellular oscillators combine to determine the master circadian rhythm, influencing various periodic functions such as sleep-wake cycles.
• The intrinsic master circadian rhythm is slightly longer than 24 hours but is synchronized to the 24-hour day through exposure to environmental light.
• Melatonin secretion is a specific marker of circadian clock activity and is closely tied to the biological clock's output and phase.
• Circadian rhythm disorders often present as inappropriate sleep-wake timing, leading to insomnia or excessive sleepiness.
• Treatments for circadian rhythm disorders that do not consider chronobiological factors may be ineffective or harmful.

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