The suprachiasmatic nucleus (SCN) is a tiny paired cluster of about 10,000 neurons sitting just above the optic chiasm. It is the body's master circadian clock, keeping a roughly 24-hour rhythm that is reset each day by light detected by the retina.
| Location | Anterior hypothalamus, directly above the optic chiasm on either side of the third ventricle |
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| Connections |
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| Blood Supply | Small perforating branches of the anterior cerebral and anterior communicating arteries |
Generates and synchronises daily rhythms of sleep and wakefulness, body temperature, hormone release (including melatonin and cortisol) and many other body functions.
Disruption of SCN timing contributes to jet lag, shift work disorder and delayed or advanced sleep phase disorders. Bright light therapy and timed melatonin act by shifting the SCN clock. Tumours or surgery near the optic chiasm can disrupt circadian rhythm, and SCN degeneration with age may contribute to fragmented sleep in dementia.
A mismatch between the internal clock and the desired sleep schedule, such as delayed sleep phase, causing insomnia at night and sleepiness in the day.
Insomnia and excessive sleepiness from working at times that conflict with the SCN-driven circadian rhythm.
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