Abstract
Have you ever had to adjust to a new time zone and noticed that it takes a while before you start to feel normal again? By shifting your sleep and activity schedule, you have altered the pattern of your body’s circadian rhythms. Human beings, like many other living things, have a number of internal processes that show a distinct circadian rhythm. The most obvious is our sleep cycle, with activity during the day, followed by sleep during the night. Circadian rhythms have also been demonstrated in humans for changes in body temperature, heart rate, alertness, and physical performance in sports. In this human biology science fair project, you will investigate human circadian rhythms by measuring body temperature and reaction time at different times of day.Objective
In this human biology science fair project, you will measure how body temperature and reaction time vary throughout the course of a day.
Introduction
In order to stay healthy and to function efficiently, living things must coordinate their internal processes with the external world. The most obvious feature of our environment that most creatures have to respond to is the daily cycle of light and dark. Biological processes that follow this 24-hour cycle, such as our sleep-wake cycle, are said to follow a circadian rhythm. One of the best-known circadian rhythms in humans is the daily change in body temperature. We tend to be at our coolest in the early morning and at our warmest in the late afternoon and early evening. Other circadian rhythms include hormone levels, alertness, muscle strength, and heart rate. The controlling regulator for these cyclic processes within the body is thought to be the hypothalamus, which is in the brain.
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| Figure 1. Overview of circadian cycles in humans. This diagram depicts some of the circadian patterns that occur in humans. Note that the clock is on a 24-hour cycle, so that 3:30 p.m., for example, is noted as 15:30. The hormone melatonin, which is a key regulator of the internal circadian clock, peaks in concentration at 21:00 (9:00 p.m.). (Wikipedia, 2008.) |
Any change in the circadian cycle (such as jet lag and other conditions associated with travel) requires a certain period for readjustment. Jet lag can cause excessive sleepiness and a lack of daytime alertness in people who travel across time zones. Another factor that can affect circadian rhythm is work schedule. For instance, people who work at night are more prone to on-the-job injuries because their circadian rhythm is off-balance with the light and dark times of day.
According to William Garret (see Bibliography), "Reaction time peaks in the early evening at the same time as the maximum body temperature. This is partially because the nerve conduction velocity increases 2.4 meters per second (m/s) for every 1°C increase in body temperature."
Do you think Garret is correct that your reaction time is fastest in the early evening? When do you think it lowest? And how much difference is there? Find out in this human biology science fair project by measuring body temperature and reaction time at various times during the day. Reaction time will be measured using online tests that are based on how fast you respond with your mouse to visual cues on the computer screen. You will then chart your results to graphically show how your temperature and reaction times vary during the course of the day.
Terms, Concepts and Questions to Start Background Research
Bibliography
To learn more about the biology of circadian rhythms, visit this website at the University of Utah:
This test from the British Broadcasting Corporation (the BBC) tests your reaction time by measuring how fast you are able to shoot escaping sheep with a tranquilizer:
This website from the Exploratorium Museum, in San Francisco, California, tests your ability to react to a 90-mile-per-hour fastball:
Materials and Equipment
Experimental Procedure
In these experiments, you will need to make sure you get the best possible data so that the variation in temperature and reaction time can be measured accurately. Your body temperature may vary from 1 to 2 degrees Celsius. Perform each trial three times and average the results.
Variations
Credits
David Whyte, PhD, Science Buddies
Last edit date: 2008-11-04 11:40:00
If you like this project, you might enjoy exploring careers in Human Biology & Health.
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