Purpose: To have a better understanding of what neurons look like, how they are interconnected and how learning changes those connections.

Procedural overview: Create your own data table to study prepared microscope slides of neurons from different types of nervous system tissue and create model neurons to demonstrate how connections among the neurons are altered during learning.

Approximate class time: 30 to 50 minutes.

Materials:

• Activity Guide for Students: How Do Neurons Form Connections?
• Microscopes (preferably with 40x, 100x and 400x power)
• Prepared microscope slides of nervous system tissue (Discovering Nerve Tissue Types Self-Study Unit by Carolina Biological Supply Company or Triarch Nervous Tissue Slides)
• Pipe cleaners in a wide variety of colors (look for extra-large pipe cleaners too)
• Wire cutters or scissors to cut pipe cleaners
• Sticky notes
• Cell phone cameras or other cameras

Notes to the teacher:

This activity has two halves, observing real neurons under the microscope and making pipe-cleaner models of neurons, which can be done in either order. Unless you have a large number of microscopes and prepared slides, you can have half the students use the microscopes while the other half work with the pipe cleaners, and then switch.

Neuron modeling activity notes: If students would like to see diagrams of neurons when creating their pipe-cleaner neurons, you could provide them with any of these:

• Campbell Biology Ch. 48 (Neurons, Synapses, and Signaling) and Ch. 49 (Nervous Systems)
• The University of Washington’s Neuroscience for Kids website provides diagrams and other activities for modeling the nervous system.

Students can use their cell phones or other cameras to take photos of their groups of pipe-cleaner neurons before, during and after learning something. Depending on your preference, they can present their photos in class or submit them via email or as a printout. If you are teaching about chemical structure, this might be a good opportunity to further explore the structure of some common neurotransmitters and receptors with students and talk about intermolecular attraction. Students may include the general structures of neurotransmitters and receptors in their pipe-cleaner models as well.

Neuron observation activity notes: If time permits, have students create their own data table for this activity. They will need to read through the entire procedure for this part to determine what types of slides they are observing and what observations they are trying to collect about each one. If they are working in pairs, allow them time to individually read through the procedure and decide all key information before collaborating with a partner. If creating a data table and writing detailed, efficient observations are skills you are teaching your students, you may want to collect and grade this activity.

Student instructions and questions with answers

Neuron modeling activity: Use the following set of instructions to create pipe cleaner models of neurons and take photos of the neurons interacting while they “learn” something. Write down your answers to the questions along the way, and be prepared to present your models and photos to the teacher or the rest of the class.

Procedure:

1. Use pipe cleaners to make several model neurons. You could make each neuron a different solid color, or you could choose a more elaborate color scheme if you would like. Look up several diagrams to prepare your neurons. Feel free to make neurotransmitters out of additional pipe cleaners or other materials provided by your teacher. Just remember, a neurotransmitter will chemically fit — meaning it will physically fit and be attracted to — a receptor on another neuron, so you’ll need to make receptors too. Make at least three complete neurons, or more if you have enough pipe cleaners and time.

For the cell body of a neuron, students might make a ball from one pipe cleaner. For dendrites, they may attach several short pieces of pipe cleaner to the ball. For an axon, students could attach one long pipe cleaner to the ball.

2. What are the roles of the cell body, the dendrites and the axon in a real neuron?

The cell body performs essential functions to keep the cell alive, the dendrites are the “input” to sense signals from other neurons and the axon is the “output” to send signals to other neurons.

3. Please note that this next step is an extreme oversimplification of neural connections made while learning to complete a task. The focus of this exercise is to determine how individual neurons communicate, and relate this concept to the larger networks of neural connections made during learning. Decide what role each neuron will play in a task to be learned, and label each neuron with a sticky note. For example, in a simple model of Pavlov’s dog, the “food” neuron fires when the dog sees food, the “bell” neuron fires when the dog hears a bell, and the “slobber” neuron fires to make the dog drool in anticipation of eating. Dogs come pre-wired with the axon of the food neuron connected to the dendrites of the slobber neuron. If the dog always hears a bell when food is presented, the dog’s brain learns to connect the axon of the bell neuron to the dendrites of the slobber neuron. Through a process called long-term potentiation, the slobber neuron realizes that it always fires at the same time the bell neuron fires, so it should strengthen its connection to the bell neuron. What roles do your model neurons play? What makes each one fire?

Student answers will vary.
 

4. What will your model neurons learn, and how?

Student answers will vary.
 

5. Connect the neurons, as they would be before learning. If one neuron is communicating with a second, the end of the first neuron’s axon should be nearly connected to one of the dendrites of the second neuron. If you’re using neurotransmitter models, show the chemicals leaving one neuron and being accepted by another. If a neuron is not communicating with the others, it can be near the other neurons but not touching them, or neurotransmitters may not be accepted by that cell. Take a photo or video of your network of neurons, making sure the labels on each neuron are visible.
 

6. In this state before learning has occurred, what does your network of neurons do? What has it not yet learned to do?

Student answers will vary.
 

7. Now make the appropriate adjustments to your neurons and take a photo or video of the neurons during the learning process.

A new synapse between two neurons is being made, a dendrite of the receiving neuron can be near the axon of the transmitting neuron. If you are using neurotransmitters and receptors, a few new receptors should be formed on the newly receiving neuron. Make sure the labels on each neuron are visible in the photo.
 

8. Make a final adjustment to your neurons, and take a photo or video of the neurons after the learning process.

A firm new link should be established between the dendrite of the receiving neuron and the axon of the transmitting neuron. If you are using neurotransmitters and receptors, many new receptors should have formed on the dendrites of the newly receiving neuron. Make sure the labels on each neuron are visible in the photo.
 

9. In this state after learning has occurred, what does your network of neurons do? What has it learned to do that it did not do before?

Student answers will vary.
 

10. What have you learned about the structure of a neuron from this activity?

Neurons have dendrites for input and an axon for output. Neurotransmitters are the means of chemical communication between neurons.
 

11. What have you discovered about learning from this activity?

If two previously unconnected neurons always fire at the same time, they learn that they should be connected together and are chemically altered so a new communication can be made.
 

12. If you had more time and more pipe cleaners, how could you make your model neuron network more elaborate or more scientifically accurate?

Student answers will vary.
 

Neuron observation activity: Use the following set of instructions to observe prepared slides of various types of neurons under a microscope. Start at the lowest power, focus on the colored layer of the slide and make observations. Move to the next higher power, refocus and make more observations. Make sure you observe different areas of each slide. Write down your observations.

Before you begin, read through the additional instructions below and create a clearly labelled data table for all of your observations.

Procedure:

1. Observe a slide of cerebral cortex. What overall shapes or structures do you see for the cerebral tissue? Which way(s) do neurons point in the sample? What shapes are the individual neurons? Can you identify cell bodies, dendrites and axons? Can you see connections between neurons? What does the cerebral cortex do? Draw a simple sketch to show where cerebral tissue is located in a human brain.

Depending on the specific slide you obtain, students may be able to see ridges and folds of cerebral tissue at lower power and neurons and their connections at higher power. Depending on how the tissue is sliced, students may see only cut-off parts of some neurons. The cerebral cortex is the outer layer of the brain and plays a role in conscious thought.
 

2. Observe a slide of cerebellum. What overall shapes or structures do you see for the cerebellar tissue? Which way(s) do neurons point in the sample? What shapes are the individual neurons? Can you identify cell bodies, dendrites, and axons? Can you see connections between neurons? How does the cerebellar tissue appear similar to or different from the cerebral cortex? What does the cerebellum do? Draw a simple sketch to show where cerebellar tissue is located in a human brain.

Depending on the specific slide you obtain, students may be able to see ridges and folds of cerebellar tissue at lower power and neurons and their connections at higher power. Depending on how the tissue is sliced, students may see only cut-off parts of some neurons. Cerebellar neurons may appear more densely packed and more organized than cerebral cortical neurons. The cerebellum is located at the lower rear of the brain and is involved in relaying instructions to muscles.

3. Observe a slide of spinal tissue. What overall shapes or structures do you see for the spinal tissue? Which way(s) do neurons point in the sample? What shapes are the individual neurons? Can you identify cell bodies, dendrites and axons? Can you see connections between neurons? What does spinal nervous tissue do? Draw a simple sketch to show where spinal tissue is located in a human body.

Depending on the specific slide you obtain, students may be able to see a cross section or a longitudinal section of bundles of neurons (mostly axons). The spinal neurons relay signals from the brain to muscles, and from receptors in the body to the brain.
 

4. Observe a slide of motor neurons. What overall shapes or structures do you see? Which way(s) do neurons point in the sample? What shapes are the individual neurons? Can you identify cell bodies, dendrites and axons? Can you see connections between neurons? What do motor neurons do? Draw a simple sketch to show where motor neurons located in a human body.

Most commercially available motor neuron slides show individual motor neurons that have been removed from their original tissue. They have large, well-defined cell bodies. The bodies of motor neurons are located in the spinal cord, and their axons extend to target muscles that they control in the body.
 

5. Observe a slide of a peripheral nerve. What overall shapes or structures do you see? Which way(s) do neurons point in the sample? What shapes are the individual neurons? Can you identify cell bodies, dendrites and axons? Can you see connections between neurons? What do nerves do? Draw a simple sketch to show where nerves could be located in a human body.

Depending on the specific slide you obtain, students may be able to see a cross section or a longitudinal section of one or more nerves (mostly axons). Such nerves relay signals from the brain to muscles, and from receptors in the body to the brain. Please note that the spinal neurons and peripheral neurons essentially play the same role in the body. The peripheral neurons are located in tissues outside of the spinal tissue.
 

6. How are the nervous tissue samples similar to or different from your pipe cleaner model?

Student answers may vary.
 

7. Based on your microscope observations, how could you make the pipe cleaner model more scientifically accurate?

Student answers will vary.