Summary
The suprachiasmatic nucleus synchronises body clocks to light through melatonin and clock genes.
In depth
The SCN receives light via melanopsin-containing retinal ganglion cells, regulates melatonin release and clock gene cycles (PER, CRY, CLOCK, BMAL1; Nobel 2017). Misalignment causes jet lag and shift work disorders.
Sleep stages show distinct EEG patterns. Sleep deprivation impairs attention and memory. Melatonin timing and light exposure shift rhythms.
Example: teenagers' circadian rhythms shift later.
The molecular clock in each cell depends on a transcription-translation feedback loop: CLOCK and BMAL1 activate Period and Cryptochrome genes, whose proteins (PER, CRY) inhibit CLOCK/BMAL1 and are degraded, giving a period of about 24 hours (Hall, Rosbash and Young, Nobel Prize 2017). The SCN synchronises peripheral clocks in organs through hormones and body temperature. Light, especially blue (about 480 nm) detected by melanopsin, resets the clock; melatonin from the pineal rises at night. Chronotypes (larks and owls) vary with genes (PER3) and age.
Shift work and jet lag cause misalignment linked to metabolic and cardiovascular risks; timing of meals, exercise and light exposure help to reset the clock. Sleep is controlled by the ventrolateral preoptic area (promotes sleep), orexin neurons in the hypothalamus (promote wakefulness), and brainstem REM circuits. Loss of orexin causes narcolepsy. Chronotherapy times drugs to the body clock.
Example: the clock continues in constant darkness with a period that is close to but not exactly 24 hours (free-running).
Frequently asked questions
What is Sleep and Circadian Rhythm?
The suprachiasmatic nucleus synchronises body clocks to light through melatonin and clock genes.
Which area of biology covers Sleep and Circadian Rhythm, and how advanced is it?
Sleep and Circadian Rhythm is one of the 54 topics in Neuroscience. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Hypothalamus and Pituitary, Neural Circuits and Oscillations, Voltage-Gated Ion Channels.
Can you give an example of Sleep and Circadian Rhythm?
Blue light in the evening can delay sleep.
What should I learn before Sleep and Circadian Rhythm?
Work through the Beginner topics in Neuroscience first, such as Nervous System, Neuron, Central and Peripheral Nervous Systems, then return to Sleep and Circadian Rhythm. Advanced topics assume the Intermediate vocabulary.
What topics are related to Sleep and Circadian Rhythm?
The closest topics to Sleep and Circadian Rhythm are Hypothalamus and Pituitary, Neural Circuits and Oscillations, Voltage-Gated Ion Channels, Hippocampus and Memory Consolidation. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Sleep and Circadian Rhythm?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Sleep and Circadian Rhythm. To practise the whole of Neuroscience, use the Neuroscience quiz.
How is Sleep and Circadian Rhythm different from Hypothalamus and Pituitary?
Sleep and Circadian Rhythm: The suprachiasmatic nucleus synchronises body clocks to light through melatonin and clock genes. Hypothalamus and Pituitary: The hypothalamus links the nervous and endocrine systems by controlling pituitary hormone release. Read both side by side and note what each one explains.
How should I study Sleep and Circadian Rhythm step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Hypothalamus and Pituitary and explain the difference aloud. Finally, take the Neuroscience quiz and come back to this page for any question you miss.