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~ Back to Articles Index Page ~  It's the end of the day and you still have a ton of work in front of you. Despite your best efforts, your body just isn't cooperating and you find yourself slumping in your chair, blinking and rubbing your eyes and dreamily drifting off to thoughts of the comfy bed calling to you from the other room. Don't blame yourself; this is your circadian rhythm kicking in telling the rest of your body, despite what you mind wants, that it's time to shut down and you can't beat it so you might as well join it.  Circadian rhythms are physical, mental and behavioral changes that follow a roughly 24-hour cycle, responding primarily to light and darkness in [your] environment. They are found in most living things, including animals, plants and [even the tiniest of] microbes.1 The term "circadian" comes from the Latin word circa, meaning "around", and diem or dies meaning "day". The study of circadian rhythms is called chronobiology ("chrono", from the Greek word meaning time). Your Biological Clock(s) You've probably heard the phrase "biological clock". Well, these really do exist (on a molecular level) in cells throughout your body. They control circadian rhythm which is orchestrated and coordinated by a "master clock" in the brain.  Deep inside the brain, sitting right above the pituitary gland at about the size of a pearl, sits the hypothalamus, an important player in the autonomic nervous system (the motor subdivision of the peripheral nervous system that controls body activities automatically). The hypothalamus manages numerous important functions in the body, including temperature, water balance, metabolism, the pituitary gland, and many drives such as thirst, appetite, pain and pleasure. The "master clock" consists of a group of approximately 20,000 nerve cells called the suprachiasmatic nucleus or SCN and is located in the hypothalamus. Circadian Rhythm and How It Affects Us We are taught in school that 24 hours equals one day. Our built-in circadian rhythm knows that a certain percentage of those 24 hours are daylight and the rest is darkness. Because it is an integral part of our autonomic nervous system, our circadian rhythm communicates to our body that certain functions must be performed during daylight hours (growth, rejuvenation) and that others are to be attended to at night (repair, detoxification). There are clear patterns of brain wave activity, hormone production, cell regeneration and other biological activities linked to this daily cycle. How does it know when it is light and when it is dark? That's simple; light and temperature levels in your immediate environment are two of the more effective signals. The circadian rhythm allows for the drive for sleep following a cycle and the body is ready for sleep and for wakefulness at different times of the day.  If your days and nights are interfered with by artificial lights or chemical stimulants, your natural rhythm shifts out of alignment. The good news is that your internal clock endeavors to reset itself daily to the 24-hour cycle of the Earth's rotation. This makes sense because it is the Earth's rotation that keeps one side of the Earth in darkness (night) and one side in bright sunlight (day) once every 24 hours. If your circadian rhythm cannot restore itself, certain methodologies such as light therapy can be very helpful. Because of this sensitivity to day and night, dark and light, it becomes obvious as to why our bedtime routines should include lower lighting, softer sounds and less stimulation than our daytime activities. When darkness falls, your internal biology begins to change. Melatonin, normally present only in very low levels in the body during the day, is secreted by the pineal gland generally starting around 9:00 pm each evening. (Read all about melatonin and its effects on our body by clicking here). This increase in melatonin is measurable in blood and saliva levels. Also, your core body temperature begins to drop, usually reaching its minimum by 5:00 am, and plasma levels of cortisol change. Conversely, when light enters your bedroom window in the morning, your body is signaled to begin the daylight portion of the 24-hour cycle. Have you ever noticed that it's harder to wake up when it's overcast and inclement outside? That's because not enough sunlight is getting through to your hypothalamus. Leaving your curtains open so that sunlight can stream in is a sure fire way to naturally help reset your circadian rhythm each morning. One other possible explanation is that overcast mornings leave us with the impression that the day hasn't sufficiently warmed enough yet for us to get out of bed as temperature is also one of the a.m. "reset" buttons for the circadian rhythm. A Healthy Circadian Rhythm Among people with healthy circadian clocks, there is a continuum of chronotypes from "larks", ("morning people" who prefer to sleep and wake early), to "owls" ("evening people" or "night people"), who prefer to sleep and wake at late times. Whether they are larks or owls, people with normal circadian systems:
Circadian Rhythm Sleep Disorder Circadian rhythm sleep disorders are a family of sleep disorders affecting the timing of sleep. People with circadian rhythm sleep disorders are unable to sleep and wake at the times required for normal work, school and social needs. They are generally able to get enough sleep if allowed to sleep and wake at the times dictated by their body clocks. Unless they have another sleep disorder (such as sleep apnea), their sleep is of normal quality. There are two types of circadian rhythm sleep disorders; extrinsic and intrinsic. Simple examples of extrinsic disorders could include jet lag or shift work. Intrinsic examples could include:
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can wake in time for what they need to do in the morning, and fall asleep at night in time to get enough sleep before having to get up.
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