Reflexes

Pupil to Pupil

For grades 3-12

Make the lights in the room dim. After a few minutes, look at the eyes of another person and note the size of the pupil (the black center spot in the middle of the eye). Turn on the bright room lights. Check the size of the pupil again. The pupils should now be smaller. This is the pupillary response: it "automatically" keeps out excessive light that may damage the eye.

Materials:

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Jump to It!

For grades K-12

Here's a quick demonstration of reflexes...first talk about how the brain and the rest of the nervous system controls movement. Then, suddenly slam a book on a table to create a loud noise. Ask the class and count the number of students who:

  1. Twitched
  2. Moved their heads
  3. Blinked their eyes
  4. Put their hands up
  5. Screamed

Reflexes are used to protect the body without us having to think about what is happening...reflexes get us away from objects that might hurt us, before they hurt us. For example, if you put your hand on a hot stove, your immediately remove your hand BEFORE the message, "Hey, my hand is on a hot, burning stove", gets to your brain.

Materials:

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Knee Jerk Reflex (Patellar Reflex)

For grades 6-12

The knee jerk reflex is one we are are familiar with...the doctor hits your knee and your leg kicks out. Try it! Have a partner sit with his or her legs crossed so that his leg can swing freely. Hit his leg just below the knee with the side of your hand. DO NOT USE A HAMMER!!!! The leg will kick out immediately (if you hit the right place).

The knee jerk reflex (seen in the figure to the right) is called a monosynaptic reflex. This means that there is only 1 synapse in the neural circuit needed to complete the reflex. It only takes about 50 milliseconds of time between the tap and the start of the leg kick...that is fast. The tap below the knee causes the thigh muscle to stretch. Information is sent to the spinal cord. After one synapse in the ventral horn of the spinal cord, the information is sent back out to the muscle...and there you have the reflex.

Materials: NONE

For more information on the knee-jerk reflex, see:

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Think Fast!

For grades 3-9

Our built-in reflexes really do protect us. Another demonstration of these built-in capabilites is the blink reflex. Have a student stand behind a see-through barrier like a window or a wire screen. Throw a cotton ball at the person. Did he blink? Probably. This is the blink reflex and serves to protect our eyes from damage.

Materials:

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How Fast are You?

For grades K-12

Unlike the other activities on this reflex page, this project does not test a simple reflex. Rather, this activity is designed to measure your response time to something that you see.

Get a ruler (or a yardstick or candy bar). Hold the ruler near the end (highest number) and let it hang down. Have another person put his or her hand at the bottom of the ruler and have them ready to grab the ruler (however, they should not be touching the ruler). Tell the other person that you will drop the ruler sometime within the next 5 seconds and that they are supposed to catch the ruler as fast as they can after it is dropped. Record the level (inches or centimeters) at which they catch the ruler (you can convert the distance into reaction time with the chart below). Test the same person 3 to 5 times (vary the time of dropping the ruler within the 5 second "drop-zone" so the other person cannot guess when you will drop the ruler).

Here is a table to convert the distance on the ruler to reaction time. Remember that there are 1,000 milliseconds (ms) in 1 second.

Distance of catch Reaction Time
(in seconds)
2 in (~5 cm) 0.10 sec (100 ms)
4 in (~10 cm) 0.14 sec (140 ms)
6 in (~15 cm) 0.17 sec (170 ms)
8 in (~20 cm) 0.20 sec (200 ms)
10 in (~25.5 cm) 0.23 sec (230 ms)
12 in (~30.5 cm) 0.25 sec (250 ms)
17 in (~43 cm) 0.30 sec (300 ms)
24 in (~61 cm) 0.35 sec (350 ms)
31 in (~79 cm) 0.40 sec (400 ms)
39 in (~99 cm) 0.45 sec (450 ms)
48 in (~123 cm) 0.50 sec (500 ms)
69 in (~175 cm) 0.60 sec (600 ms)

This reaction time experiment required visual information (the movement of the ruler) to travel to your brain. Then your brain sent a motor command ("grab that falling ruler") to the muscles of your arm and hand. If all went well, you successfully caught the ruler!!

Questions and Comparisons

Materials:

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More on Reflexes

There is also a great experiment where you can compare your auditory and visual response times on-line. Make sure you keep track of your responses while you do this experiment. However, to use this page, you need to have the "shockwave plug-in" for your browser.

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"Neuroscience for Kids" activities are copyrighted by Eric H. Chudler, Ph.D.
of the University of Washington

Please send comments and suggestions to Dr. Chudler at chudler@u.washington.edu.

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