Biological Rhythms

There are daily rhythms to many of our physiological functions and activities....our sleep, body temperature, alertness, neurotransmitter levels, etc. Many of these rhythms run on a cycle of about 24 hours. Rhythms that run on this 24 cycle are called "Circadian Rhythms". "Circa" comes from the latin word meaning "around" and "dies" comes from the word "a day". Even if you lived in a dark cave and didn't know what time it was, the cycles would still exist and they would hold to the 24 hour rhythm. While neuroscientists are not exactly sure how the brain keeps track of time, there are several areas of the brain that may be involved. One of the possible "pacemakers" in the brain is a part of the hypothalamus called the suprachiasmatic nucleus.

Experiment 1: The Ups and Downs of Body Temperature

Grades 3-12
One circadian rhythm that is easy to keep track of is your own body temperature. Get an oral thermometer like the one you use when you are sick. Make sure you know how to use it properly!! Measure your temperature every 2 hours from the time you get up in the morning to the time you go to sleep. (If you can't measure your temperature every 2 hours, then just measure it as often as it is feasible).
Don't eat or drink anything right before you take your temperature. Make sure to take your temperature the same way every time and that you read the temperature VERY ACCURATELY....the differences in your body temperature are only a few 0.1 of a degree. Chart your body temperature with time...use the X axis for "Time of Day" and Y axis for "Body Temperature". Do you see a pattern?

An additional activity to do with the body temperature measurements is to combine the reaction time experiment. Measure your reaction time to catching the ruler and plot your "catch times" with your body temperature. Is there a correlation? Is your reaction time faster or slower with warmer body temperatures?


Experiment 2: Rhythms All Around

Grades 3-12
People have biological rhythms...what about other creatures? Many schools have classroom pets - a rat, hamster, fish or frog. If your class has a pet, study its behavior to see if you can determine any cycling patterns. For example, if you have a rat, observe the amount of time it spends eating, walking and sleeping at different times of the day. Check on it every 2 hours and watch it for 10 minute periods. It is best if a group of students helps out. Assign 1 behavior to each student. Therefore, one person can measure the amount of time spent eating, another person can watch for sleeping, etc. Do not disturb the animal while you are observing it. Chart the amount of time spent in each behavior at different times of the day. Keep track of it for several days. Are there any consistent patterns?


Experiment 3: Built in Stopwatch

Grades 3-9
Sometimes it seems like time flys by....sometimes it drags on forever. How good are you at estimating time? Do you have a built in stopwatch? Try to estimate the length of 1 minute. Have someone with a stopwatch say "Go". When you think 1 minute has past, say "Stop". Check to see how close you were. Try several times and see if your performance gets better. Do "timing" stategies work, like counting seconds with "1-mississippi, 2-mississippi, 3-mississippi,...."?


See Circadian Rhythms and Oscillating Reactions for more about nature's rhythms.

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