Acting Potential

Printer-friendly format

How fast can a message travel? Could your nerves communicate as fast as a telegraph wire or a cell phone? It may depend upon what you are asking them to do.

In this exercise you'll explore National Science Education Content Standard C: Life Science - Structure and function

Middle School:

Specialized cells perform specialized functions in multicellular organisms. Groups of specialized cells cooperate to form a tissue, such as a muscle. Different tissues are, in turn, grouped together to form larger functional units, called organs. Each type of cell, tissue, and organ has a distant structure and set of functions that serve the organism as a whole.

Behavior is one kind of response an organism can make to an internal or environmental stimulus. A behavioral response requires coordination and communication at many levels, including cells, organ systems, and whole organisms. Behavioral response is a set of actions determined in part by heredity and in part from experience.

High School:

Multicellular animals have nervous systems that generate behavior. Nervous systems are formed from specialized cells that conduct signals rapidly through the long cell extensions that make up nerves. The nerve cells communicate with each other by secreting specific excitatory and inhibitory molecules. In sense organs, specialized cells detect light, sound, and specific chemicals and enable animals to monitor what is going on in the world about them.

What You'll Need:

• A large space
• A stopwatch
• A whistle
• A meter stick

Keeping Safe:

Remember to move slowly and carefully. Don't share the whistle without washing it.

Procedure:

Tell a student to close his or her eyes and hold out both hands. Say: "When I touch your right index finger, I would like you to wiggle your left index finger." Perform the action several times. Then think about where the message must go to do this: first from your right finger to your brain, and then from your brain to your left finger. How far do you think this is? To find out, measure the distance from the receptor to the brain and back to the finger muscle with your meter stick. Compare your results with other students, and then find the average for students in your class.

Join hands with all your fellow students in an open area. The first student should have a stopwatch. The last student should have a whistle.

The first student hits the "starter" on the stopwatch and squeezes the second student's hand at the same time. When that student feels the squeeze, he or she should squeeze the next student in line. When the squeeze has reached the last student in the line, he or she should blow the whistle. When student #1 hears the whistle, he hits "stop" and records the time.

Let someone else be "student #1" and try again. Repeating several times and averaging will help you get a better answer.

Now add up all the distances that your message had to travel, and divide it by time to find the speed of transmission of your message.

Questions:

1. Check out the speed of transmission through nerves that researchers have established. Was yours faster or slower?

2. Why might it be different?

3. Using the simple reflex animation, show where the message is electrical and where it is chemical.

4. Electrical messages in wires travel almost a million times faster than messages down nerves. How are the two alike? How are they different? (See the chart comparing transmission speeds.)

Answers:

1. Yours was no doubt significantly slower.

2. The simulation includes nerves, synapses, and muscles, not just axon transmission.

3. The message is electrical (ionic) in the axon and chemical in the synapse.

4. Electrical messages in wires move nearly at the speed of light; they consist of electrons. These messages are represented by ions. Both rely on the energy potential of oppositely charged particles.