Circadian Rhythm and Sleep

When you feel the effects of jet lag, or when you feel tired after working a rotating shift during the week, what actually is happening is that your body's circadian rhythm has been affected. The word circadian is derived from the Latin words circa diem which translated into English, means about a day. As far as the human body is concerned, one day refers to a 24-hour period.

Although most commonly associated with humans and their sleep patterns, circadian rhythm also has a direct influence on our blood pressure, our body temperature and our body's production of hormones. Together these internal changes tell our bodies when it is time to sleep and to wake and how our moods will be at any given time.

Rhythm is a very big part of nature. For example, we know that the Earth completes a rotation every 24-hours and that year after year, the seasons change from winter to spring to summer to autumn and then back again to winter. Therefore, circadian rhythm plays a significant role in animals' lives as well. The most notable example of an annual natural rhythm is the migration of countless species of birds every year.

When it comes to the sleep-wake cycle, there are two primary environmental forces at work: light and temperature. Circadian rhythm can also be affected by other stimuli such as the sound of your alarm clock and what and when you have eaten, and in women, their menstrual cycles.

Internally, circadian rhythm is influenced by an 'internal clock' located in the part of brain called the hypothalamus. Specifically, two large clusters of neurons situated on either side of the brain called the Suprachiasmatic nuclei or SCN is considered the body's master clock. The SCN work with other genes to help the body keep track of time. The stimulation and/or release of different chemicals, hormones and neurotransmitters is how the body knows when it is time to fall asleep and to wake up, when it's time to eat and when it's time to have intercourse and more.

When it comes to sleep, the following is a simplistic overview of how the circadian rhythm works. At the first sign of daylight, the body begins to produce hormones and neurotransmitters including serotonin and cortisol. These help the body transition into an awakened mode by increasing body temperature and blood pressure. Likewise, as daylight fades, the body begins to release melatonin, the main signal that tells the body to begin lowering blood pressure and to prepare itself for sleep.

When the body's circadian rhythm is in balance, it dictates the proper timing and release of these important chemicals, hormones and neurotransmitters. However, when the body's circadian rhythm is 'off' this timing and release is knocked out of balance. A prolonged imbalance can and often does lead to the development of a number of sleep disorders and emotional disturbances. It would seem then that being healthy and happy is all about keeping your circadian rhythm in check.