• Background

    Think fast! It might feel like you think and react instantly, but it actually takes a little bit of time for nerve signals to travel. That's why when someone throws something at you unexpectedly, it's challenging to react quickly enough to catch it. Something that we react to in our environment is called a stimulus.

    The amount of time between sensing and responding to a stimulus is called reaction time. Reaction time is usually so fast that we have to measure it in milliseconds. One millisecond is 1/1000 of a second.


    How fast is your reaction time?


    Based on what you know about how fast you and other people can catch balls, stop bicycles, hit volleyballs, etc., how fast do you think your reaction time is? Also base your hypothesis on what you have learned about nerves and nerve signals. (Remember a hypothesis does not have to be right, but it should be based on good logic and on knowledge we have gathered so far.) One second would be 1000 milliseconds, 1/2 of a second would be 500 milliseconds, 1/4 second would be 250 milliseconds. Write your hypothesis in your science notebook.



    1. Before beginning your experiment, make a data table in your science notebook (See directions in the data section).
    2. Ask a parent or sibling to help you with this experiment.
    3. Hold out your thumb and index finger, about three centimeters apart, ready to pinch together.he d
    4. Have a parent or sibling hold the ruler with the 0 cm mark hanging just between your fingers.
    5. At a random second, they should drop the ruler, and you should catch it. It is important that you don't know exactly when they are going to drop the ruler.
    6. Measure to the nearest centimeter, or if you are able, to the nearest tenth of a centimeter, how far the ruler dropped before you caught it.
    7. Repeat steps 2 through 5 four more times, for a total of 5 trials.
    8. Find the average number of centimeters the ruler fell.
      To find the average:
      • Step 1: Estimate your average. The average should be the "normal" amount. It won't be the highest amount or the lowest amount. It will be somewhere in-between them.
      • Step 2: Add together all 5 trials.
      • Step 3: Divide the total by the number of trials.
      • Step 4: Check your answer with your estimate. Does your answer make sense?
      • Finally: Enter your average in your data table.
    9. Use the reaction time graph and your average number of centimeters to figure out how many milliseconds your average reaction time was.


    We will be doing 5 trials, and since this is an observational study (not really an experiment), we only have one condition. Try making your data table first; then check to see if it matches one of these. It doesn't need to be exactly the same, but it does need to have an organized place to write each piece of data. Record your data in the data table in your science notebook.


    Based on your data, what is the answer to our question? What does this teach us about nerve signals? What further questions does it make you want to ask about how nerve signals travel? Write your rough draft of your conclusion in your science notebook.