Pupil to Pupil
MethodsDim the lights in a room. 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 the room lights back on. Check the size of the pupils again. The pupils should now be smaller. This is the pupillary response: it "automatically" keeps out excessive light that may damage the eye.
Jump to It!
MethodsHere's a quick demonstration of reflexes. Talk to a group of people 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:
MethodsThe knee jerk reflex is one that you may have had tested at a check up at the doctor's office. In this test, the doctor hits your knee at a spot just below your knee cap 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 because there is only one synapse in the circuit needed to complete the reflex. It only takes about 50 milliseconds 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 then sent to the spinal cord. After one synapse in the ventral horn of the spinal cord, the information is sent back out to the thigh muscle that then contracts.
MethodsOur built-in reflexes really do protect us. Another demonstration of these built-in capabilities 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.
|Did you know?||People typically blink about 15 times per minute. If you are awake for 16 hours each day, then you blink approximately 14,400 each day! (Source: Schiffman, H.R., Sensation and Perception. An Integrated Approach, New York: John Wiley and Sons, Inc., 2001)|
How Fast are You?
MethodsUnlike 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. For example, if you caught the ruler at the 8 inch mark, then your reaction time is equal to 0.20 seconds (200 ms). Remember that there are 1,000 milliseconds (ms) in 1 second.
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 caught the ruler!!
Questions and Comparisons
Carolina Biological Supply Company also sells a Reaction Time Ruler Set that includes three rulers with msec gradations, one instruction book and recording sheets. Cost = $22.50/set.
More Reaction Time Experiments
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Neuroscience for Kids