1. Begin the lesson by displaying a transparency of Master 3.1, Two Types of Cells, on the overhead projector. Ask students to make observations about the two cells.

Focus discussion on similarities and differences between the two cells. Students may say that the top cell is smooth and round, while the bottom cell is long and thin. They may comment that although both cells have a cell body and a nucleus, there appear to be some “extra” parts sticking out of the bottom cell.

2. Explain to the class that the top cell is the most common type of animal cell, such as a skin cell. The bottom cell is a special cell that passes information through the body. It is a nerve cell, or neuron.

Assessment:
Listen to student responses to assess their understanding that information flows in only one direction through neurons. This concept is key to the following activities.

Explain briefly that a neuron is made up of three parts: the dendrites, the cell body, and the axon.

3. Ask students to stand and form a line around the classroom. Explain that they will model information flow through a neural pathway.

A neural pathway is a path of information flow through the body. Each student represents one neuron along the pathway.

4. Ask students to hold out their arms, forming a fist with their right hand and leaving their left hand open.

Students should stand close to one another but leave a space between adjacent hands. Explain that as neurons, the open left hand of each student represents their axon end, and their right fist represents their dendrite end.

5. Tell students that they will be passing information through their model pathway by using their open hand to tap the fist of the person next to them.

Content Standard C:
All organisms are composed of cells—the fundamental unit of life. Living systems at all levels of organization demonstrate the complementary nature of structure and function. Specialized cells perform specialized functions in multicellular organisms.

Start the flow of information through the pathway by tapping the fist of the rightmost student of the line with your left hand. Each student should pass the information along by using their axon (left hand) to tap the dendrite (right fist) of the student next to them. Allow the information to be passed through the entire line of students.

6. Now ask a student in the middle of the line to face the opposite direction from the rest of the line, leaving the same hands open and fisted. Once again, start the flow of information by tapping the fist of the rightmost student in the line. What happens to the signal?

To make the point of directional information flow, you may want to reinforce the idea that the open hand can only send information and the fist can only receive information. The signal should stop at the student facing the opposite direction from the rest of the line.

7. Ask students what this experiment suggests about information flow through neurons.

Information flows through neurons in one direction only.

1. Ask students to explain the difference between a voluntary response and an involuntary response.

Content Standard C:
Behavior is one kind of response an organism can make to an internal or environmental stimulus.

A voluntary response is an action we choose to perform. We do not choose to perform an involuntary response; instead, our bodies respond without a conscious choice.

2. Ask students to provide examples of voluntary and involuntary responses.

Voluntary responses include walking, talking, eating, or reading books. Involuntary responses include changes in heartbeat, breathing, digestion, or blinking.

3. Explain to the class that they will investigate an involuntary response known as a reflex action. Ask, “What is a reflex action?”

Students should have a general understanding that a reflex involves a quick, automatic response by their bodies to an input from the environment.

4. Your students are probably familiar with the knee-jerk reflex. Ask for student volunteers to describe and/or demonstrate this reflex.

Students may describe the knee-jerk reflex as something they have experienced when they visit the doctor. The doctor taps below their kneecap with a small hammer, and their leg kicks out. Some students may wish to demonstrate this reflex on their own knee. Alternately, you may choose to demonstrate the reflex on yourself by sitting on your desk and hitting your knee. In addition, you may wish to have all students try this reflex on themselves.

Some students may be unable to get the knee-jerk reflex to work on themselves and may become concerned that there is something wrong with them. Reassure these students by explaining that finding the precise location to tap below the knee can be difficult for nonphysicians. Furthermore, if students consciously tighten their leg muscles, the knee-jerk reflex either may not occur or may occur only subtly.

5. Explain to students that they will be working in groups to construct the neural pathway that controls the knee-jerk reflex. Divide the class into groups of two or three students each.
6. Give stapled sets of Master 3.3(a, b, and c), Neuroscience Reference Manual, to each group.

Explain that the Neuroscience Reference Manual contains essential information for this activity. Point out several sections of the manual that will be helpful to students as they construct their neural pathways. Part 1 of the manual describes the parts of the nervous system; Part 2 describes neural signaling and the three main types of neurons; and Part 3 contains details about reflex actions and voluntary actions.

Tip from the field test: Introducing the reference manual before students start working emphasizes the importance of this resource and encourages students to use this information to help them complete the activity.

Assessment:
Collecting the completed masters from students at the conclusion of this lesson provides an opportunity for formal assessment of students’ understanding of neural pathways.

7. Give each group one copy of Master 3.4, Building a Reflex Pathway. Explain to students that they will work with their group members to construct a neural pathway for the knee-jerk reflex.

Students use colored pencils to draw neurons on Master 3.4, Building a Reflex Pathway. This master contains an outline of a person with the brain, spinal cord, and thigh muscle, as well as the heart, lungs, and liver, drawn in.

8. Give each group pencils of three different colors. Explain to students that they should use these pencils to represent the three types of neurons as they construct their pathway. Only one of each type of neuron used needs to be drawn as a representation. Instruct groups to use the Neuroscience Reference Manual to help them complete their drawings.

Students should read, interpret, and evaluate information in the Neuroscience Reference Manual to determine how to construct the pathway. Students should pay particular attention to the types of neurons described in Part 2 of the manual and to the “Reflex Actions” section in Part 3 of the manual. As student groups work, walk around the classroom to monitor their progress. Be available to answer questions, but encourage students to consult the appropriate section(s) of the Neuroscience Reference Manual before you answer.

9. As students construct their diagrams, ask them to discuss the following questions with their group members:
   1. Why did their group choose the parts they did?
   2. How did they put those parts together?
   3. How does information flow through the pathway?

You may wish to write these questions on the board so students can refer to them. This step helps students prepare for their presentations (Step 10).

10. When groups are finished, ask one group to diagram their reflex pathway on a transparency of Master 3.4, Building a Reflex Pathway.

Students should explain the following:

1. Why their group chose the parts they did.
2. How they put those parts together.
3. How information flows through the pathway.

A correctly completed pathway should have these attributes:

• The pathway should include only the spinal cord, one sensory neuron, and one motor neuron.
• The sensory neuron should have its dendrites on the thigh and its axon terminals on the pelvic region of the spinal cord.
• The motor neuron should have its dendrites on the spinal cord and its axon terminals on the thigh muscle.

If the pathway is correct, information would flow as follows:

• Information (the hammer hitting the knee) is received by the dendrites of the sensory neuron in the thigh and flows to the axon terminals of the sensory neuron in the spinal cord.
• Within the spinal cord, information flows from the axon terminals of the sensory neuron to the dendrites of the motor neuron.
• Information flows from the dendrites of the motor neuron in the spinal cord to the axon terminals in the thigh muscle, resulting in the leg kicking out.

Students should use the correct components of the pathway and place the components in the correct orientation. This leads to reinforcing the discovery they made in Activity 1 of this lesson, that information can only travel through a neural pathway in one direction.

11. When the presentation is completed, ask the other groups if they agree with the pathway of the first group. If another group disagrees, ask a representative from that group to present their pathway using another transparency of Master 3.4.

The new representative should explain their group’s pathway to the class. Student descriptions should consist of the components, construction, and flow of information outlined above. Encourage the class to examine each pathway carefully based on the information provided in the Neuroscience Reference Manual. Does the pathway have enough parts? Too many parts? Are the parts connected in the correct way? Would information flow through the pathway correctly? Why or why not?

Assessment:
Assess students’ understanding by listening to their explanations and reasoning.

Allow presentations to continue until all alternate pathways have been explained to the class. Through discussion of the pathways presented, the class should be able to create a correct pathway by consensus. At the end of the discussion, all students should be able to construct the reflex pathway correctly and describe the flow of information through it.

1. Give one copy of Master 3.5, Building a Voluntary Response Pathway, to each group.
2. Explain to students that they will work with their group members to construct a neural pathway for the voluntary leg movement involved in kicking the soccer ball. Instruct groups to complete their drawings with only those parts that are involved directly in the pathway, using the Neuroscience Reference Manual as a guide.

Explain to the class that the path of information flow begins with the eyes—that is, seeing the soccer ball coming toward them. The response is moving the leg to kick the ball.

Students should read, interpret, and evaluate information in the Neuroscience Reference Manual to determine how to construct the pathway. Students should pay particular attention to the types of neurons described in Part 2 of the manual and to the “Voluntary Actions” section in Part 3 of the manual. As student groups work on their pathways, walk around the classroom to monitor their progress. Be available to answer questions, but encourage students to consult the appropriate section(s) of the Neuroscience Reference Manual before you answer.

3. As students construct their diagrams, ask them to discuss the following questions with their group:
   1. Why did their group choose the parts they did?
   2. How did they put those parts together?
   3. How does information flow through the pathway?

Writing these questions on the board allows students to refer to them as they work. This step helps students prepare for their presentations (Step 4).

4. When groups are finished, ask one group to diagram their voluntary response pathway on a transparency of Master 3.5, Building a Voluntary Response Pathway.

Student descriptions should include these components:

1. Why their group chose the parts they did.
2. How they put those parts together.
3. How information flows through the pathway.

A correctly completed pathway should have these attributes:

• The pathway includes the brain, the spinal cord, one sensory neuron, one interneuron, and one motor neuron.
• The sensory neuron should be drawn on the figure with its dendrites on the eye and its axon terminals on the brain.
• The interneuron should be drawn on the figure with its dendrites on the brain and its axon terminals on the pelvic region of the spinal cord.
• The motor neuron should be drawn on the figure with its dendrites on the spinal cord and its axon terminals on the thigh.

If the pathway is correct, information would flow as follows:

• Visual information (seeing the soccer ball) received by the dendrites of a sensory neuron in the eye flows to the axon terminals of that sensory neuron in the brain.
• Within the brain, visual information is transferred from the axon terminals of the sensory neuron to the dendrites of an interneuron. Visual information is processed by the interneuron, which produces response information (kicking the ball).
• Response information flows from the dendrites of the interneuron in the brain to the axon terminals of that interneuron in the spinal cord.
• Within the spinal cord, response information flows from the axon terminals of the interneuron to the dendrites of a motor neuron.
• Response information then flows from the dendrites of the motor neuron in the spinal cord to the axon terminals of the motor neuron in the leg, directing the foot to kick the incoming soccer ball.

Students should use the correct components of the pathway and place them in the correct order and orientation. This leads to the following discoveries: neurons are specific to a certain job, and information flows through a neural pathway in only one direction.

5. After the presentation is completed, ask the other groups if they agree with the pathway of the first group. If another group disagrees, ask a representative from that group to present their pathway using another transparency of Master 3.5.

Assessment:
Assess students’ understanding by listening to their explanations and reasoning.

The new representative should explain their group’s pathway to the class. Student descriptions should consist of the components, construction, and flow of information outlined above. Students may produce a variety of incorrect answers. Encourage the class to carefully examine each pathway based on the information provided in the Neuroscience Reference Manual. Does the pathway have enough parts? Too many parts? Are the parts connected in the correct way? Would information flow through the pathway correctly? Why or why not?

Allow presentations to continue until all alternate pathways have been explained to the class. Through discussion of the pathways presented, the class should be able to create the correct pathway by consensus. At the end of the discussion, all students should be able to construct the voluntary leg movement pathway correctly and describe the flow of information through it.

1. The first pathway students constructed was for the knee-jerk reflex. Ask students, “If a physician tested the knee-jerk reflex on each of us, would everyone’s response be the same?”

Students should generally agree that the knee-jerk reflex would be the same for everyone tested by the physician.

2. The second pathway students constructed was for the voluntary leg movement to kick a soccer ball. Now ask students to imagine that they are actually playing soccer. They notice that the ball is headed straight for them. What would they do?

Students may provide a variety of answers, including kicking, bouncing, or catching the ball, moving out of its way, standing still and allowing the ball to hit them, or not being on the soccer field in the first place. In general, students should answer that they would somehow interact with the soccer ball.

Assessment:
Asking students to write their answers to the questions in Steps 3 and 4 allows them to organize their thoughts and reflect on what they have learned in this lesson. For a formal assessment of student learning, you can review the written materials.

3. Point out that a variety of responses was provided for the soccer ball scenario, as opposed to the same response by everyone for the knee-jerk reflex. Ask students, “Why were you able to have different responses for the soccer ball scenario?”

Students should explain that the soccer ball scenario required a voluntary response. Since voluntary responses involve choice, students were able to choose their response to the soccer ball scenario, which allowed their responses to be different from their peers’.

4. Ask students why they were not able to choose the response to the reflex action. What is the difference between the two pathways?

Students should recall that the voluntary response pathway included the brain, while the reflex pathway did not. Since the brain is required to make a choice, students were unable to choose their response to the reflex action.