Normally, when it is light outside, your body knows that it is time to be awake, and when it is dark outside, that it is time to be asleep. So how does your body know when to be asleep and when to be awake?
Within the brain is a structure called the suprachiasmatic nucleus, or the SCN. The SCN, also considered the body’s “clock,” controls the body’s circadian rhythms, which the National Institute of General Medical Sciences defines as the “physical, mental and behavioral changes that follow a roughly 24-hour cycle, responding primarily to light and darkness in an organism’s environment.”
The SCN sends signals to another structure in the brain, the pineal gland, which produces the hormone melatonin. The name “melatonin” may sound familiar, as a synthetic form of the hormone is sold as a supplement to help individuals fall asleep. Melatonin signals to the body when it is time to sleep and when it is time to be awake.
When it is light outside, the optic nerves relay the light information to the SCN, which signals to the pineal gland to decrease melatonin production. When it is dark outside, the optic nerves signal to the SCN that there is less light out, and thus the SCN relays to the pineal gland the message to produce more melatonin, which makes the individual sleepy.
Some people can suffer from disrupted circadian rhythms, which affects their sleep. For example, people who travel to different time zones can experience jet lag. So if there is a three hour time difference, the individual’s biological clock feels she is getting up at 4 a.m. instead of 7 a.m.
Disruption in the normal sleep-wake cycle can result in different sleep problems, such as insomnia. A disrupted circadian rhythm can also occur in individuals who work the night shift, as they are working during the night and sleeping during the day.
The National Institute of Neurological Disorders and Stroke noted that individuals who do shift work are at increased risk for health problems due to their altered sleep, including digestive disturbances, emotional problems and heart problems.
So how can a disrupted circadian rhythm be treated? Individuals who have jet lag may undergo light therapy, in which they are exposed to special lights in an attempt to set their biological clocks to the new time zone. Another option is using melatonin supplements. However, the National Institute of Neurological Disorders and Stroke warned that new issues may arise with long-term use of the supplement.
References
National Institute of General Medical Sciences. Circadian Rhythm Fact Sheet. Web. 9 March 2012
http://www.nigms.nih.gov/Education/Factsheet_CircadianRhythms.htm
National Institute of Neurological Disorders and Stroke. Brain Basics: Understanding Sleep. Web. 9 March 2012
http://www.ninds.nih.gov/disorders/brain_basics/understanding_sleep.htm
Reviewed March 9, 2012
by Michele Blacksberg RN
Edited by Jody Smith