Circadian Rhythm | Circadian Rhythms | Circadian Rhythm Sleep Disorders

Circadian Rhythm Sleep Disorders

Circadian rhythm sleep disorders are disruptions of the natural biological cycles that control how people are attuned to night and day.

The term circadian comes from Latin words that literally mean around the day.

The daily cycle of life, which includes sleeping and waking, is called a circadian (meaning "about a day") rhythm, commonly referred to as the biologic clock.

Hundreds of bodily functions follow biologic clocks, but sleeping and waking comprise the most prominent circadian rhythm. The sleeping and waking cycle is approximately 24 hours.

There are patterns of brain wave activity, hormone production, cell regeneration, and other biological activities linked to this 24-hour cycle. The circadian "clock" in humans is located mainly in the suprachiasmatic nucleus (SCN), which is a group of cells located in the hypothalamus (a portion of the brain).

Circadian rhythms are important in determining human sleeping patterns. Shifting into or out of daylight savings time, traveling across time zones (which can cause jet lag), or working at a job that involves late evening or nighttime work can affect the body's circadian rhythm.

In a person with a circadian rhythm sleep disorder, the body is unable to maintain its normal rhythm. The natural sleep schedule changes so that the person is out of phase with day and night.

However, factors outside the body, especially bright light, help to set the internal clock to the day cycle or time schedule appropriate to where the person is.

Common Circadian Rhythm Disorders

  • Jet Lag or Rapid Time Zone Change Syndrome: Jet lag is the common term for time zone change syndrome, a temporary set of symptoms that occur when people travel across more than two time zones. The resulting change in daylight hours can cause excessive daytime tiredness, headaches, moodiness, tired muscles, and a general "worn-down" feeling. This syndrome consists of symptoms including excessive sleepiness and a lack of daytime alertness in people who travel across time zones.
  • Shift Work Sleep Disorder: Shift work can wreak havoc with the body's circadian rhythm: many people never fully adapt to their new schedule. Maintaining regular bedtime schedules, even on days off, can help reduce the effects of shift work.
  • Delayed Sleep Phase Syndrome (DSPS): Delayed sleep phase syndrome (DSPS) occurs when people fall asleep more than two hours later than their desired bedtimes.
  • Advanced Sleep Phase Syndrome: The main characteristic of advanced sleep phase syndrome is when the major rest period begins earlier than desired. People fall asleep earlier than normal, and have unusually early awakening times. This syndrome results in symptoms of evening sleepiness, an early sleep onset, and waking up earlier than desired.
  • Non 24-hour sleep wake disorder: Non 24-hour sleep wake disorder is a condition in which an individual has a normal sleep pattern but lives in a 25-hour day. Throughout time the persons sleep cycle will drift in and out of normal societal norms, sometimes falling asleep at a later time and waking up later, and sometimes falling asleep at an earlier time and waking up earlier.


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