Outline OVERVIEW Rationale: This lesson is intended to introduce students to the process of synaptic transmission, which is how one neuron communicates with another neuron. Using the pain pathway as a model, this lesson covers how the electrical signal of the action potential is converted into a chemical signal at the nerve terminal. Objectives: Students will be able to describe how neurons change the electrical signal of the action potential into a chemical signal at the synapse. Students will be able to order the steps of synaptic transmission. Activities: The students begin this lesson by building the pain pathway and brainstorming ways in which the electrical signal of the action potential could be converted into a chemical signal that can cross the synaptic cleft. After being introduced to all the characters involved in synaptic transmission, students work in groups to order the steps of the process. The lesson continues with a Socratic discussion reviewing each step of synaptic transmission. Homework: The homework assignment focuses on the importance of which ion channels open or close in response to neurotransmitter. Through this assignment students are introduced to excitatory and inhibitory synapses. The Lesson Plan Lesson : How do our neurons communicate with each other? 1. Do now (5-7 min): Students model the pain pathway using clay. 2. Discussion (5-7 min): Compare ideas/mechanisms for the Do Now. Introduction to the characters of synaptic transmission. 3. Activity (15-20 min): Card game: put the steps of synaptic transmission in order. Socratic discussion reviewing steps of synaptic transmission. 4. Wrap Up (3 min): How do drugs modulate synaptic transmission? 5. Homework: Does it matter which ions flow into the postsynaptic cell? 2Lesson Unit1.2 6. Materials: 1. Printed Materials Lesson worksheet Synaptic transmission cards 2. Additional Materials Clay 99
The Lesson Worksheet is included in the Materials Folder for this lesson. 1. DO NOW Give the students a copy of the Lesson Worksheet and have them complete Part 1: Do Now with a partner. This part of the worksheet asks students to model the neurons in the pain pathway. Once the students have created a neuronal pathway, they are asked to brainstorm mechanisms to change the electrical signal of the action potential into a chemical signal at the synapse so that one neuron can communicate with another within the pathway. Pain Pathway Slide 2 Use this slide to facilitate a discussion about the model pain pathways students created in the Do Now. 2. Discussion Since the pain pathway is not the focus of today s lesson it is being used as a model to provide connection to yesterday s lesson and to get the students thinking about the communication between neurons try to keep this specific discussion brief. Focus on the fact that the students will have more than one neuron within the pathway and therefore neurons must have a way to communicate with each other. Ask the students How many neurons do you have within your model pain pathway? How many neurons are in the pain pathway on the slide? Students will likely have at least two neurons within their own pathways. The pathway modeled on the slide has four neurons sensory neuron, interneuron, motor neuron and projection neuron Animate slide 3 to show the students the red box within the spinal cord. Tell the students that we will now focus on how neurons communicate with each other. Slide 3 100
Synaptic Transmission 2 Ḋiscussion Converting an Electrical Signal to a Chemical Signal: Use this slide to facilitate a discussion about the students mechanisms to convert the electrical signal of the action potential into a chemical signal. Use this slide to introduce the students to the idea that there are chemicals called neurotransmitters in the presynaptic terminal. Slide 5 Slide 4 Ask the students- How does the axon send signals? Electrically. Ask the students- How does the synapse send signals? Chemically. Ask the students - Share your mechanisms for converting the electrical signal of the action potential into a chemical signal at the synapse. The students will probably have a variety of different mechanisms. For each mechanism ask other students to comment on how feasible they think that particular solution is. Good answers will include some mechanism for detecting an electrical signal and converting it into a chemical signal. Tell the students that the process by which the electrical signal of the action potential is converted into a chemical signal at the synapse is called Synaptic Transmission. Ask the students- Do they know what the red dots are within the blown up image? The red dots represent neurotransmitters which are the chemicals that transmit the signal from one neuron to another by crossing the synapse. It is important that the students become familiar with the term neurotransmitter. There are many different types of neurotransmitters. In our last unit, we will further discuss the neurotransmitter dopamine and its involvement in the reward pathway. For now, just make sure the students know the term neurotransmitter and are aware that our body has many different types of neurotransmitters. 101
2. Discussion Tell the students that the neurotransmitters are stored within synaptic vesicles, represented by the white circles in the blown up image. Ask the students if they can think of a benefit to putting neurotransmitters within vesicles? Prepackaging neurotransmitters in vesicles prepares them for release into the synaptic cleft. Ask the students- Do they know what the blue shapes represent within the blown up image? The blue shapes represent receptors which are proteins that recognize and bind to the neurotransmitters. Ask the students- What changed between the last slide and this slide? The neurotransmitters (red dots) got released into the synaptic cleft. The neurotransmitter attached to the postsynaptic receptors (blue shapes). The postsynaptic receptors changed shape/opened in response to neurotransmitter binding. The Stage: Use this slide to introduce the students to the idea that we will discuss the process of synaptic transmission as if it were a play with characters performing actions on a stage. Slide 7 Synaptic Transmission Use this slide to demonstrate how neurotransmitters cross the synaptic cleft and bind to postsynaptic receptors. Slide 6 This slide introduces the students to the location at which synaptic transmission occurs or The Stage. The slide is animated so you can display the location of the presynaptic cell, synapse, and postsynaptic cell during the discussion. Ask the students- in this picture where is the presynaptic cell? To the left in this picture. The term presynaptic comes from pre meaning before the synapse. 102
Discussion Ask the students- Where is the synapse? In the center of this picture. Focus on the fact that the synapse (sometimes called the synaptic cleft) is actually the space between two neurons. Ask the students- Where is the postsynaptic cell? To the right in this picture. The term postsynaptic comes from post meaning after the synapse. The Characters Use this slide to introduce the characters of synaptic transmission. The students should already know some of the characters, but others will likely be new. This slide is animated, so with each question, advance the slide to label the characters on the slide. Slide 8 Ask the students- What is within the synaptic vesicles? Neurotransmitters. Ask the students- What is represented by the red arrow? Give them a hint that red arrows usually signify electrical potentials. The action potential. The students will likely not know about reuptake transporters, voltagegated Ca2 + channels, or Ca2 + sensitive proteins, so introduce the students to each of these characters. Tell the students that the axon terminal also contains voltage-gated Ca2 + channels, represented by the green circles in this figure. Explain that voltage-gated means that they respond to changes in voltage by changing shape. Tell the students that the axon terminal also contains proteins that can respond to changes in Ca2 + levels. These proteins are called Ca2 + sensitive proteins and are represented by the blue diamonds. Tell the students that the axon terminal also contains reuptake transporters to pump excess neurotransmitter out of the synapse back into the presynaptic cell. Ask the students- What are the white circles within the presynaptic terminal? Synaptic vesicles. Ask the students- What do neurotransmitters bind to on postsynaptic cells? What is represented by the blue circles? Postsynaptic receptors. 103
3. Activity The Play Use the next set of slides (slides 10-17) to review the correct order of the steps of synaptic transmission with the students. How do the characters work together to complete synaptic transmission? Now that the students know all the characters and the stage involved in synaptic transmission, have them work in groups to determine how synaptic transmission works. Divide the students into groups of three or fewer students and give each group a set of the Synaptic Transmission Card Sort. Have the students order the cards to describe the process of synaptic transmission. Slide 10 The file containing the cards for this activity is included in the Materials Folder for this lesson. You will need to print the file and cut it to actually make the cards. Slide 9 After giving the students 5-7 minutes to sort the cards, review the steps as a class using the next set of slides in the PowerPoint. Ask the students- How must synaptic transmission start? What triggers the synaptic terminal to release neurotransmitters? The action potential invades the axon terminal. Slide 11 Ask the students- What character within our play is able to detect the entrance of the action potential? Who is voltage-sensitive? Voltage-gated Ca 2+ channels. 104 104
3. Activity What do the voltage-gated Ca 2+ channels do in response to the action potential? They open. Ask the students- What happens once the voltage-gated Ca2+ channels are open? What do Ca 2+ sensitive proteins do once they detect Ca 2+? They fuse synaptic vesicles to the membrane. Slide 14 Ca 2+ flows into the cell. Slide 12 Ask the students what happens once the proteins fuse the synaptic vesicles to the membrane? Neurotransmitters (NTs) are released into the synaptic cleft. Slide 13 Slide 15 Ask the students what character within our play is able to detect changes in Ca 2+? Ca 2+ sensitive proteins. Ask the students- Where do neurotransmitters bind after they are released into the synaptic cleft? Postsynaptic receptors. 105
3. Activity Slide 16 Slide 17 Ask the students- What does neurotransmitter binding to receptors change within the postsynaptic cells? Ion channels open on the postsynaptic membrane, allowing ions to flow into the cell. Ask the students- Why could allowing ions to flow into the postsynaptic cell be important? This is an important concept and one that will be revisited in the homework and then again in the next lesson, but introduce it now. Allowing ions to flow into the postsynaptic cell begins the process of that cell being able to reach threshold and fire an action potential, which is represented by the red arrow in the postsynaptic cell. Ask the students- What happens to excess neurotransmitters left within the synaptic cleft? They are degraded by enzymes or pumped back into the presynaptic cell. 106
4. Wrap Up What happens if...? Slide 19 If time allows, use the next two slides to give a concrete example of how drugs modulate the process of synaptic transmission. Slide 18 Ask the students- What would happen if you took a drug that destroyed the Ca2+ sensitive proteins that fuse synaptic vesicles to the membrane? You wouldn t be able to release synaptic vesicles. This would prevent the presynaptic neurons from signaling to the postsynaptic neuron. Animate the slide to show the students the text box with the answer. Tell the students that Botox destroys the proteins that fuse synaptic vesicles with the membrane. By stopping vesicle release, Botox prevents muscle contraction which prevents fine lines and wrinkles not that any of them need that right now. Synaptic Transmission Use this slide to introduce the homework which has the students review the steps of synaptic transmission and think about whether it matters which ions flow into the postsynaptic cell. How Botox works Use this slide to explain to the students how Botox works. Slide 20 107
4. Wrap Up The Lesson Worksheet is included in the Materials Folder for this lesson. Remind the students on the main goal of synaptic transmission by asking them - What is the primary goal of synaptic transmission? To communicate a signal from one neuron to another neuron. Does it matter which ions flow into the postsynaptic cell? Use this slide to get the students to start thinking about whether or not it matters which ions flow into the cell. Slide 21 Ask the students- Since the goal of synaptic transmission is to send a signal from one neuron to another, does it matter which ion channels open and which ions flow into the postsynaptic cell? For homework, the students will have to respond to this question. Homework Worksheet: Ion channels For homework have the students complete Part 2 of the Lesson Worksheet. This part of the worksheet asks students to review the steps of synaptic transmission by labeling a diagram. Then the students are asked to write a paragraph about whether it matters which ions flow into the postsynaptic cell. This homework is intended to introduce students to the idea of excitatory and inhibitory synapses. 108