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The Sleep-Wake Cycle

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Our sleep-wake cycle is a complex feedback loop that works through the interaction of hormones, light, genetics, environment and behavior. It is dictated partially by our circadian rhythm, which is roughly a 24-hour cycle that helps govern processes such as hormones, body temperature, and sleep-wake cycles.

A major player in the sleep-wake cycle is the suprachiasmatic nucleus, or SCN. This is a cluster of approximately 20,000 nerve cells located in the hypothalamus of your brain. The SCN controls the circadian rhythm and is sometimes called the body’s “master clock.”

According to the National Institute of General Medical Sciences:

“The body’s master clock, or SCN, controls the production of melatonin, a hormone that makes you sleepy. Since it is located just above the optic nerves, which relay information from the eyes to the brain, the SCN receives information about incoming light. When there is less light-like at night-the SCN tells the brain to make more melatonin so you get drowsy.”

A disruption in your circadian rhythm will affect your sleep. Things such as working night or swing shifts, jet lag, or irregular sleep schedules due to stress, medications or illness can disrupt the cycle. Abnormal circadian rhythms are associated with some mental illnesses, including seasonal affective disorder, depression, and bipolar disorder.

Circadian rhythm scheduling of chemotherapy (called chronotherapy) has been linked to better outcomes in cancer treatment. Conversely, disrupted circadian rhythms seem to be a factor in developing some cancers.

There are some natural interventions that can help reset your circadian rhythm. Bright light early in the morning, melatonin supplements later in the day, and a rigid sleep schedule can help, as well as keeping the room you sleep in dark and cool. Melatonin is not appropriate for everyone. Some people have a paradoxical reaction to melatonin supplements that causes them to be agitated instead of sleepy. It’s important to discuss even over the counter medications with your health care provider, in case you have a contraindication to taking them.


Bader MK & Littlejohns LR. (2004).

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We value and respect our HERWriters' experiences, but everyone is different. Many of our writers are speaking from personal experience, and what's worked for them may not work for you. Their articles are not a substitute for medical advice, although we hope you can gain knowledge from their insight.

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