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The Brain: Understanding Neurobiology

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Teacher’s Guide

Lesson 2—Explore/Explain

Neurons, Brain Chemistry, and Neurotransmission (Page 2 of 2)

Procedure

National Science Education Standards icon
Content Standard A:
Formulate and revise scientific explanations and models using logic and evidence.

Content Standard A:
Communicate and defend a scientific argument.

Content Standard C:
Cell functions are regulated.

Activity 2: How Do Neurons Communicate?

Before doing this activity, students need to have a good understanding of the difference between an axon and a dendrite and the direction of information flow along these neuronal fibers. Remember that dendrites carry information toward the cell body and axons carry information away from the cell body. Also, students need to understand the terms presynaptic and postsynaptic.

In this activity, students will use the Internet to enhance what they deduce from a print-based activity. If students don’t have access to the Internet, a print modification of the activity is also provided. The procedures for each version of the activity are the same except for Step 4. When you reach that point in the activity, select the appropriate step.

  1. Ask students to consider what purpose synapses serve.

Some students are likely to respond correctly that synapses serve to connect neurons (synapses do not connect neurons physically, but they do connect them functionally). This enables neurons to communicate by passing signals between them.

  1. Remind students that the brain is an organ that regulates body functions, behaviors, and emotions. Neurons are the cells that fulfill these functions. How do neurons do this?

Neurons control these functions by passing signals across the synapse from one neuron to the next. These signals dictate whether the receiving neuron is activated.

  1. Divide the class into groups of three students. Give each group a copy of Master 2.3, How Do Neurons Communicate? Ask students to look at and discuss the diagrams and, as a group, write a summary of how they believe the neurons are interacting at each step.

At this point, students will not know the correct terminology for the structures and molecules involved in neurotransmission. Encourage students to use whatever terms they wish to describe what is represented in the diagrams. The main point of this activity is for students to begin to understand that specific events happen both within a neuron and between neurons during neurotransmission.

Sample Answers to Master 2.3

Students are likely to use a variety of terms in their responses. Although at this point the use of correct vocabulary is not the critical issue, some students will use the terms axon, dendrite, presynaptic, and postsynaptic that they learned in Activity 1.

Diagram #1 The presynaptic neuron ending has large circles in it. The large circles have smaller circles inside. There are two sets of bars that cross the end (membrane) of the presynaptic neuron. The postsynaptic neuron has two rectangular-shaped boxes on the end (membrane) of the neuron.
Diagram #2 Nothing has changed except that there is a lightning bolt (electrical signal) and an arrow indicating that the lightning bolt is moving toward the end of the presynaptic neuron.
Diagram #3 One of the larger circles is now in contact with the end of the presynaptic neuron. Another circle is now releasing the small circles into the space between the neurons.
Diagram #4 The small circles are in the space between the neurons and one small circle is now attached to the box-shaped figures on the end of the postsynaptic neuron.
Diagram #5 The lightning bolt symbol (electrical signal) is at the postsynaptic neuron now. The arrow indicates that it is moving away from the neuron ending.
Diagram #6 The small circles are no longer attached to the box-shaped figures on the postsynaptic neurons. The arrows seem to indicate that the small circles are now moving back into the presynaptic neuron and going back into the larger circles.
  1. Have the students watch the neurotransmission animation on the Web site or read Master 2.4 aloud.
Web activity icon

Students access the animation by going to the Web site and clicking on Lesson 2—Neurons, Brain Chemistry, and Neurotransmission. They may wish to view the animation several times because it is packed with information.

Now that students have explored neurotransmission by completing Master 2.3, the animation will help them incorporate the proper terminology and clarify any misunderstandings.8

print activity icon

If computers are not available, display a copy of Master 2.4, Neurons Communicate by Neurotransmission. Read through the material with the students.

Students should not copy the information on Master 2.4. The goal is for students to listen to the reading to help them learn the proper terminology and clarify their understanding of neurotransmission.

  1. After the students have been introduced to the proper terminology by the animation or the reading, give each student a copy of Master 2.5, Neurotransmission. Ask them to revise their summary of neurotransmission using the appropriate terminology. Encourage students to discuss their answers with the other members of their group.

Students may wish to watch the animation or review the reading again while doing this step. The goal is not to have students copy the explanation, but to revise their understanding of neurotransmission, incorporate the appropriate terminology, and correct any misconceptions they had from Master 2.3.

Sample Answers to Master 2.5

Diagram #1 This diagram shows the component parts of the neurotransmission process between electrical impulses.
Diagram #2 An electrical impulse travels down the axon toward the presynaptic nerve terminals.
Diagram #3 The vesicles containing neurotransmitter move toward the neuron cell membrane at the end of the axon. The vesicles fuse to the membrane and then release their contents (neurotransmitter molecules) into the synaptic cleft.
Diagram #4 The neurotransmitter is in the synaptic cleft and binds to the receptor on the postsynaptic neuron’s membrane.
Diagram #5 Neurotransmitter molecules are still bound to the receptors, and an electrical signal passes along the postsynaptic neuron away from the synapse.
Diagram #6 Neurotransmitter molecules are released from the receptors. Neurotransmitter molecules are taken back up into the presynaptic neuron through the transporter. Once inside the presynaptic neuron terminal, the neurotransmitter molecules are repackaged into vesicles.
  1. Once the groups have finished revising their summaries, hold a class discussion and put together a summary of how neurotransmission occurs. Inform students that the diagrams and Web animation are simplified models of neurotransmission. Many hundreds or thousands of receptors that can bind neurotransmitter are present in the dendrites of a postsynaptic neuron.
  2. Remind students of the reward system. The neurons that make up the reward system use a neurotransmitter called dopamine. Dopamine neurotransmission occurs as the students learned in Masters 2.3, 2.4 (print alternative), and 2.5 and the Web animation.
National Science Education Standards icon
Content Standard C:
Cell functions are regulated.

Activity 3: Do All Neurotransmitters Have the Same Effect?

Now that students understand that neurotransmitters are the chemical messengers involved in communication between neurons, students will learn that different neurotransmitters can affect neurotransmission differently.

  1. Show an overhead transparency of Master 2.6, Recording the Activity of a Neuron. Explain that scientists study the activity of neurons by recording the electrical impulses that neurons generate when they are activated, or fire. These electrical impulses are called action potentials

Master 2.6 shows a diagram of a microelectrode recording the electrical activity of a neuron in the brain. The action potentials are amplified and then analyzed by a computer that counts the number of spikes that occur during a period of time. The action potentials appear as vertical lines, or spikes, on the oscilloscope. If the recording were slowed down, the action potentials would appear similar to that shown in Figure 2.4 (see Background Information section). A signal is also sent to an audio amplifier that produces a click sound each time an action potential is generated in the neuron. The more frequently the spikes appear on the screen with accompanying audible clicks, the more frequently the neuron is firing

  1. Divide the class into groups of three. Give each group a copy of Master 2.7, Neurotransmitter Actions. Tell students that they will analyze the effects of different neurotransmitters on the activity of a neuron. Have the groups answer the questions that follow the data analysis.

After the groups have completed the questions, discuss their answers to make sure that students understand that different neurotransmitters have different effects on neurons.

Sample Answers to Master 2.7

Question 1. Why is saline applied to the resting neuron?

The resting neuron is the control for the experiment. If a scientist wants to determine what effect applying a neurotransmitter has on a neuron, he or she must have a control. The neurotransmitter applied to the other neurons would be dissolved in a saline solution, so applying saline to the resting neuron provides information about how a neuron responds to the solvent solution (in this case, a weak salt solution). If the experimental neuron does not respond in the same way as the control neuron, this indicates that the neurotransmitter applied to those neurons is the cause for the response, not the saline itself, or the act of applying any solution to the neuron.

Question 2. When the neurotransmitter glutamate is applied to the neuron, how does its activity change?

Glutamate stimulates the neuron and causes it to generate more electrical impulses.

Question 3. How does the application of the two neurotransmitters, glutamate and GABA, change the activity of the neuron?

In this case, GABA is present in high enough concentrations to override the effects of glutamate.

Question 4. Predict how the activity of the neuron would change if only GABA was applied to the neuron.

If GABA can inhibit a neuron even when glutamate is added, GABA by itself should inhibit the neuron’s activity.

Question 5. Do all neurotransmitters affect a neuron in the same way?

No, the neurotransmitters glutamate and GABA have opposite effects on the neuron’s activity.

Question 6. How would the application of glutamate to a neuron change the amount of neurotransmitter that is released from that neuron? How would the application of GABA to a neuron change the amount of neurotransmitter that is released from that neuron?

If glutamate is applied to a neuron, it causes the neuron to generate more electrical impulses. This would increase the amount of neurotransmitter that the neuron releases from its axon terminals.

If GABA is applied to a neuron, it reduces the number of electrical impulses generated by that neuron. The decreased activity in the neuron would decrease the amount of neurotransmitter that the neuron releases from its axon terminals.

Web activity icon
  1. Students can continue this activity using the simulation on the Web site of applying neurotransmitters to a neuron.

Go to the Web site. Click on Lesson 2—Neurons, Brain Chemistry, and Neurotransmission and then select Neurotransmitter Actions.

National Science Education Standards icon
Content Standard A:
Formulate and revise scientific explanations and models using logic and evidence.

Content Standard A:
Communicate and defend a scientific argument.

Content Standard C:
Cell functions are regulated.

Activity 4: One Neuron Signals Another

This activity is the most challenging one in the lesson. It requires students to integrate what they learned in Activities 2 and 3. If students successfully complete this activity, they will have a good understanding of how neurons communicate.

  1. Copy the chart from Master 2.8b, Neurons in Series, onto the board.
  2. Now that students understand that neurotransmitters can either stimulate or inhibit the generation of action potentials in a neuron, they will continue to examine how one neuron signals another in a series. Give each student a copy of Master 2.8. As a class, work through Case A on the master to determine how the stimulatory and inhibitory neurotransmitter effects alter dopamine release from the last neuron in the series. Fill in the answers on the chart.

You may wish to use an up or down arrow to indicate an increase or decrease in the activity of the neuron or the amount of neurotransmitter released from a neuron. Students may find it helpful to refer to their work on Master 2.5.

Case A

The signal molecule that affects Neuron #1 in this case is inhibitory. It reduces the chances that Neuron #1 will fire. Thus, it acts to decrease the activity of Neuron #1. If Neuron #1 is less active, it releases less neurotransmitter. Neuron #1 produces glutamate, an excitatory neurotransmitter. The decreased level of neurotransmitter released from Neuron #1 leads to a decreased level of activity of Neuron #2. If Neuron #2 is less active, it will release less dopamine.

A signal molecule influences the activity of Neuron 1 which then influences the activity of Neuron 2.

Case Does the signal molecule excite or inhibit Neuron #1? Does the activity of Neuron #1 increase or decrease? Does the amount of neurotransmitter released from Neuron #1 increase or decrease? What is the name of the neurotransmitter released from Neuron #1? Is the neurotransmitter released from Neuron #1 excitatory or inhibitory? Does the activity of Neuron #2 increase or decrease? Does the amount of dopamine released from Neuron #2 increase or decrease?
A inhibit decrease decrease glutamate excitatory decrease decrease

Tip from the field test: Students sometimes became confused by the multiple neurotransmitters involved in each case. A common misconception was the same neurotransmitter that acted to stimulate or inhibit a neuron then passed through the neuron and was released from the axon terminals at the other end. Remind students what they learned in Activity 2 regarding the fate of a neurotransmitter after it binds to, and then comes off, its receptor. The released neurotransmitter is either degraded or taken back up into the axon terminal that released it.

For the purpose of this activity, the signal molecule is a neurotransmitter. In Lesson 3, students will learn that drugs of abuse can also act in a similar way to alter neurotransmission.

  1. After the students have worked through the first example as a class, ask them to work in their small groups to complete the chart for Cases B–D. Students will determine how inhibitory and excitatory inputs contribute to the activity of a neuron that is part of a series.

As a student group finishes one of the cases (B–D), have a group member come to the board and fill in the blanks for that problem. When all of the groups are finished, ask the group that completed each line on the board to explain its answers to the rest of the class. If another group disagrees with the answer, have that group explain its reasoning. As a class, resolve the discrepancies and reach a consensus explanation. In this way, students practice critical thinking and communication skills.

Assessment icon
Assessment:
Listening to students explain their answers, defend their reasoning, and modify their responses after listening to other students explain their logic will help you assess students’ understanding of neurotransmission.

Sample Answers for Master 2.8

Case A. The signaling molecule is inhibitory. Neuron #1 releases glutamate as its neurotransmitter. Neuron #2 releases dopamine as its neurotransmitter.

The inhibitory signal molecule decreases the activity of Neuron #1. If Neuron #1 is less active, it releases less neurotransmitter. Neuron #1 produces glutamate, an excitatory neurotransmitter. The decreased amount of neurotransmitter released from Neuron #1 leads to a decreased level of activity of Neuron #2. If Neuron #2 is less active, it will release less dopamine.

Case B. The signaling molecule is excitatory. Neuron #1 releases glutamate as its neurotransmitter. Neuron #2 releases dopamine as its neurotransmitter.

The excitatory signal molecule increases the activity of Neuron #1. If Neuron #1 is more active, it releases more neurotransmitter. Neuron #1 produces glutamate, an excitatory neurotransmitter. The increased amount of neurotransmitter released from Neuron #1 leads to an increase in the activity level of Neuron #2. If Neuron #2 is more active, it will release more dopamine.

Case C. The signaling molecule is inhibitory. Neuron #1 releases GABA as its neurotransmitter. Neuron #2 releases dopamine as its neurotransmitter.

The inhibitory signal molecule decreases the activity of Neuron #1. If Neuron #1 is less active, it releases less neurotransmitter. Neuron #1 produces GABA, an inhibitory neurotransmitter. The decreased amount of neurotransmitter released from Neuron #1 leads to an increase in the activity level of Neuron #2 (less GABA = less inhibition of Neuron #2). If Neuron #2 is more active, it will release more dopamine.

Case D. The signaling molecule is excitatory. Neuron #1 releases GABA as its neurotransmitter. Neuron #2 releases dopamine as its neurotransmitter.

The excitatory signal molecule increases the activity of Neuron #1. If Neuron #1 is more active, it releases more neurotransmitter. Neuron #1 produces GABA, an inhibitory neurotransmitter. The increased amount of neurotransmitter released from Neuron #1 leads to a decrease in the activity level of Neuron #2 (more GABA = stronger inhibition of Neuron #2). If Neuron #2 is less active, it will release less dopamine.

Case Does the signal molecule excite or inhibit Neuron #1? Does the activity of Neuron #1 increase or decrease? Does the amount of neurotransmitter released from Neuron #1 increase or decrease? What is the name of the neurotransmitter released from Neuron #1? Is the neurotransmitter released from Neuron #1 excitatory or inhibitory? Does the activity of Neuron #2 increase or decrease? Does the amount of dopamine released from Neuron #2 increase or decrease?
A inhibit decrease decrease glutamate excitatory decrease decrease
B excite increase increase glutamate excitatory increase increase
C inhibit decrease decrease GABA inhibitory increase increase
D excite increase increase GABA inhibitory decrease decrease
  1. Ask students to keep their completed worksheets, Masters 2.5 and 2.8. Students will refer to these when they do activities in Lesson 3.
Web activity icon
  1. Students may continue to explore how signals from one neuron influence the target neuron by doing the online activity Neurons in Series.

To access the Neurons in Series activity, go to the Web site and click on Lesson 2—Neurons, Brain Chemistry, and Neurotransmission, and select the Neurons in Series tab.


Web activity icon Lesson 2 Organizer: Web Version
Activity 1: Anatomy of a Neuron
What the Teacher Does Procedure Reference

Remind students of the PET images from Lesson 1. Ask students to think about what composes the differently colored areas.

Step 1

Display a transparency of Master 2.1. Explain to students that the neuron is the basic functional unit of the brain and nervous system. Point out the parts of the neuron and their function.

transparency iconStep 2

Display the top half of a transparency of Master 2.2. Point out that axon terminals of one neuron end near the dendrites of another neuron.

transparency iconStep 3

Reveal the bottom half of the Master 2.2 transparency. Inform students that the connection between the two neurons is called a synapse. Explain the terms presynaptic and postsynaptic.

transparency iconStep 4

Show the transparency of Master 1.7 from Lesson 1. Discuss the reward system in terms of the neurons that form the reward system.

Step 5
Activity 2: How Do Neurons Communicate?
What the Teacher Does Procedure Reference

Ask students to consider what purpose synapses serve.

Step 1

Remind students that the brain is an organ that regulates many functions. Ask, “How do neurons fulfill these diverse functions?”

Step 2

Divide the class into groups of three. Give each group a copy of Master 2.3. Each group should work together to write descriptions of what is happening at each step.

master iconStep 3

Show the online animation How Neurotransmission Works to the class.

Web activity iconStep 4

Reconvene the student groups. Give each student a copy of Master 2.5. Ask students to work individually to revise their description of neurotransmission using the appropriate terminology. After individuals have completed their descriptions, students can discuss them with their team members.

master iconStep 5

Discuss the descriptions of neurotransmission as a class and generate a consensus summary of neurotransmission.

Step 6

Remind students of the reward system and inform them that the neurons in the reward system use a neurotransmitter called dopamine.

Step 7
Activity 3: Do All Neurotransmitters Have the Same Effect?
What the Teacher Does Procedure Reference

Show a transparency of Master 2.6. Briefly explain that scientists study the activity of neurons by recording the electrical impulses that neurons generate when they are activated, or fire. Introduce the term action potential.

transparency iconStep 1

Students return to their groups of three. Give each group a copy of Master 2.7. Ask students to work through the information and answer the questions.

master iconStep 2

Allow time for students to work through the simulation on the Web site. To access the simulation, select Lesson 2—Neurons, Brain Chemistry, and Neurotransmission from the activities menu and then Neurotransmitter Actions.

Web activity iconStep 3
Activity 4: One Neuron Signals Another
What the Teacher Does Procedure Reference

Copy the chart from Master 2.8b onto the board.

Step 1

Give one copy of Master 2.8 to each student. As a class, work through Case A to determine how stimulatory and inhibitory neurotransmitter effects alter dopamine release. Write the answers on the chart.

master iconStep 2

Have students work through Cases B–D in their teams. As teams finish, ask for teams to volunteer to fill in the blanks for one of the cases on the chart on the board. Have teams explain the answers. If teams disagree, discuss how they arrived at their answer. Work through each case until there is consensus.

Step 3

Have students keep their copies of Masters 2.5 and 2.8. Students may then do the online activity Neurons in Series.

Web activity iconSteps 4, 5
Web activity icon= Involves using the Internet.
master icon= Involves copying a master.
transparency icon= Involves making a transparency.

print activity icon Lesson 2 Organizer: Print Version
Activity 1: Anatomy of a Neuron
What the Teacher Does Procedure Reference

Remind students of the PET images from Lesson 1. Ask students to think about what composes the differently colored areas.

Step 1

Display a transparency of Master 2.1. Explain that the neuron is the basic functional unit of the brain and nervous system. Point out the parts of the neuron and their function.

transparency iconStep 2

Display the top half of a transparency of Master 2.2. Point out that axon terminals of one neuron end near the dendrites of another neuron.

transparency iconStep 3

Reveal the bottom half of the Master 2.2 transparency. Inform students that the connection between the two neurons is called a synapse. Explain the terms presynaptic and postsynaptic.

transparency iconStep 4

Show the transparency of Master 1.7 from Lesson 1. Discuss the reward system in terms of the neurons that form the reward system.

Step 5
Activity 2: How Do Neurons Communicate?
What the Teacher Does Procedure Reference

Ask students to consider what purpose synapses serve.

Step 1

Remind students that the brain is an organ that regulates many functions. Ask, “How do neurons fulfill these diverse functions?”

Step 2

Divide the class into groups of three. Give each group a copy of Master 2.3. Each group should work together to write descriptions of what is happening at each step.

master iconStep 3

Display a transparency of Master 2.4. Read through the material with the students.

transparency iconStep 4

Reconvene the student groups. Give each student a copy of Master 2.5. Ask students to work individually to revise their description of neurotransmission using the appropriate terminology. After individuals have completed their descriptions, students can discuss them with their team members.

master iconStep 5

Discuss the descriptions of neurotransmission as a class and generate a consensus summary of neurotransmission.

Step 6

Remind students of the reward system and inform them that the neurons in the reward system use a neurotransmitter called dopamine.

Step 7
Activity 3: Do All Neurotransmitters Have the Same Effect?
What the Teacher Does Procedure Reference

Show a transparency of Master 2.6. Briefly explain that scientists study the activity of neurons by recording the electrical impulses that neurons generate when they are activated, or fire. Introduce the term action potential.

transparency iconStep 1

Students return to their teams of three. Give each team a copy of Master 2.7. Ask students to work through the information and answer the questions.

master iconStep 2
Activity 4: One Neuron Signals Another
What the Teacher Does Procedure Reference

Copy the chart from Master 2.8 onto the board.

Step 1

Give one copy of Master 2.8 to each student. As a class, work through Case A to determine how stimulatory and inhibitory neurotransmitter effects alter dopamine release. Write the answers on the chart.

master iconStep 2

Have students work through Cases B–D in their teams. As teams finish, ask for teams to volunteer to fill in the blanks for one of the cases on the chart on the board. Have teams explain the answers. If teams disagree, discuss how they arrived at their answer. Work through each case until there is consensus.

Step 3

Have students keep their copies of Masters 2.5 and 2.8.

Step 4
master icon= Involves copying a master.
transparency icon= Involves making a transparency.

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