The Internal Sleep System
Body Temperature and Circadian Rhythm
Your internal biological clock, often referred to as the sleep clock or circadian clock, regulates your sleep and your daytime energy levels. This inner clock is sensitive to many factors, as you will learn later on. Your biological clock is very different from a normal clock. The biological clock is a physiological system that allows you to live in harmony with the rhythms of nature, such as the cycles of day and night and the changing of seasons. The most important function of our biological clock is that it regulates our sleep/wake cycle. This clock is located in a very small area of the brain called the within the hypothalamus. This part of the brain is often referred to as the body’s master gland because it regulates such vital functions as heart rate, breathing, blood pressure, hormone production, and body temperature! If anything, this should underline the importance of body temperature. Now that you have a basic understanding of what the sleep clock is, let us look at the specific components or variables that combine to make up this sleep clock.
The Importance of Body Temperature
A vital component of your body clock is body temperature. Our body clock regulates body temperature, and is very important with regard to sleep. We refer to the body temperature rhythm as circadian rhythm (from Latin meaning “about a day”). Let further explain circadian rhythm and the ebb and flow of body temperature during a day: In the wee hours of the early morning, your body temperature is at its lowest point and then it begins to rise before sunrise. Your temperature continues to increase throughout the day until mid afternoon when it drops a bit, and then starts rising again reaching it’s peak at about 6 PM. During the next few hours, your body temperature drops until you fall asleep, when it starts to decline rapidly until it reaches its daily low point at around 4 AM.
The variation between minimum and maximum body temperature is about 1½ degrees F. in a healthy young adult. These variations in temperature are closely linked to your daily activities, alertness, and sleepiness. As mentioned earlier, body temperature and sleep are closely related. During late morning and early evening, you are at your most active and alert when your body temperature is highest. As body temperature declines at night, you grow sleepier and less active. When your body temperature increases, your brain wave activity speeds up as well. Conversely, when body temperature declines, brain waves slow down. In other words, in order for you to start waking in the morning and for you to feel energized and alert, your body temperature must rise. Still, many people lead a lifestyle where this natural body temperature curve is not really a curve at all, but very flat! Meaning there is not a very big variation between high and low.
If there isn’t a significant rise in body temperature in the morning, your level of alertness won’t increase significantly either, or at least not rapidly. Conversely, if there is not a significant drop in body temperature at night, sleep will not come easily. This rise and fall in body temperature is what sends a signal to your brain—when to feel tired and when to feel awake. A good body temperature curve isn’t just something that comes along automatically.
Your body needs a cue to start its natural rhythm and “align” itself with the cycle of light/dark for your body temperature to rise. Similarly, in order for you to fall asleep at night, a drop in body temperature is required. If this drop does not occur, you will experience severe difficulties falling asleep! The prerequisite for this drop in body temperature to occur is that your circadian rhythm started on cue upon awakening in the morning!
What has happened to so many people in today’s fast-paced world is that they inadvertently do any number of things that inhibit this circadian rhythm and mess with the natural body temperature curve. Two of the most important factors that interfere with body temperature rhythm are your daily level of natural sunlight exposure and your daily level of activity. We’ll explore those factors in detail later on. Remember that if your cycle does not start in the morning but rather later in the day, you delay you natural rhythm, which in turn delays the drop in body temperature that is required for you to fall asleep.
Melatonin
You may have become acquainted with melatonin as a popular supplement, but melatonin is more importantly a natural hormone that is secreted by the pineal gland, a small gland nestled deep within the human brain. Scientists did not become aware of melatonin until 1958! Melatonin is one of the key components of your inner sleep system. When melatonin levels are high, you feel drowsy and tired; and conversely, when melatonin levels are low, you feel vitalized and full of energy. Sunlight and darkness regulate melatonin levels. When sunlight enters your eyes, melatonin levels decrease. This also causes a rise in body temperature. In other words, you start to feel awake.
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