Brain DeCoded with CodeX - Mission 5, Objective 4: Muscle Response

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Overview

Objective 3 showed neurons taking turns to make a rhythm. This objective names the thing that runs it. The Central Pattern Generator, or CPG, sets the rhythm of a motion and keeps it going without the brain having to issue every single order. There is also a theory here worth arguing about: that rhythmic movement could be generated by reflexes.

Students build chewing_sim, which puts a CPG on the hardware. The 180 positional servo works the jaw, the potentiometer feeds the simulation, and the screen changes color as the state changes. The interesting part is the interruption. A reflex can break a rhythm when something goes wrong, which is what happens when you bite your tongue and your jaw stops without you deciding to stop it.

This objective wires up the same peripherals as Objective 2, so setup should go faster the second time.

🎯 Project Goal: Students add code to a program that simulates the Central Pattern Generator.

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Learning Targets

I can explain the theory that rhythmic movements could be generated by reflexes.
I can explain how the CPG sets a rhythm in motion.

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Key Concepts

The Central Pattern Generator sets the rhythm of a motion.
A reflex can interrupt a rhythm if a problem occurs.

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Assessment Opportunities

Exit ticket: give an example of a motion that is set by the CPG.
Turn in the Activity Guide.
Complete the program chewing_sim.

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Success Criteria

Complete the CodeTrek steps
Program runs correctly without errors
Activity Guide is completed

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Digital Resources

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Classroom Materials

▸CodeX device and USB cable, one per student
▸Laptop/computer with Chrome browser
▸180 positional servo
▸Potentiometer and divider

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Extensions & Cross-Curricular

ExtensionFor students with programming experience, have them review the code for muscle_open() and muscle_close(). How are they alike, and how are they different? Then try writing a single function instead of two.

ExtensionStudents make adjustments to the code, such as the timing, the angles of the servo, or the colors used.

ExtensionChange the program to simulate a motion other than chewing, and adjust the text to describe the new motion.

Life ScienceHave students think about other actions that might use a CPG. What could interrupt the rhythm, and what would fix the problem so the rhythm can resume?

Lang ArtsStudents explain how the Central Pattern Generator works, in their own words.

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Vocabulary

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Central Pattern Generator (CPG) - The part of the motor neural network that sets the rhythm of a motion and keeps the rhythm going.

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New Python Code

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display.fill(RED)Fill the LCD screen with a solid color.

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Standards

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Science & Engineering Practices

Engaging in Argument from Evidence

Crosscutting Concepts

Patterns

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Preparing for the Lesson

Pull the peripherals back out: a 180 positional servo and a potentiometer with its divider per student or pair. Same setup as Objective 2, so students who kept their wiring notes will move fast.
Run the program yourself first. You want to know what a normal chewing cycle looks like before you can tell which student servos are misbehaving.
Decide how students get the Activity Guide. You can print a copy for each student or assign it digitally. They record results in it, so hand it out before they start.
Have the CodeX Peripherals Guide open or projected for the wiring questions.
Have your own CPG example and interruption ready for discussion. Chewing and biting your tongue is the obvious pair, so pick a second one if you want students to reach past the program.

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Teacher Notes

The program uses the potentiometer and 180 servo. Remind students to use the divider board with the potentiometer, and to check that the wires are connected correctly.
Students should follow the instructions on the Activity Guide and record their results.
The CPG is easiest to explain as the part that keeps going on its own. Students often assume the brain sends a separate order for every chew, and the whole point is that it does not have to.
The theory that rhythmic movement comes from reflexes is a theory, and the standards here are about arguing from evidence. It is worth letting students push on it rather than presenting it as settled.
Extensions and cross-curricular projects are included to enhance the concepts in the objective. You can use the extensions to extend students' learning.

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Lesson Outline

🗣️Warm-up / Hook

Start with a rhythm nobody is thinking about.

Ask: "When you chew, are you deciding to make each individual chew? Then who is?"
Ask: "What happens the instant you bite your tongue, and how much of that did you choose?"

Teaching tip: The tongue-bite question does the whole objective in one move. Students already know the jaw stops before they decide anything, which is the reflex interrupting the rhythm.

🔌Wiring Setup

Same peripherals as Objective 2. Get them right before any code runs.

Hand out the 180 positional servo and the potentiometer with its divider.
Students connect the potentiometer through the divider board, then connect the servo.
Check wire order on each setup. Reversed wires are still the most common reason nothing moves.
Hand out or assign the Activity Guide.

Teaching tip: Ask students who wired this in Objective 2 to help the ones who are stuck. It clears the room faster than you can, and it is a real review of the setup.

💻Student Work Time

Students build chewing_sim and run the CPG.

Students work through the CodeTrek steps, adding code to chewing_sim.
The servo works the jaw through its open and close cycle, and display.fill() changes the screen color as the state changes.
Students run the simulation and watch the rhythm hold steady on its own.
Students trigger the interruption and watch the reflex break the rhythm, then see how it resumes.
Students record their results on the Activity Guide as they go.

Teaching tip: The screen color is your debugging tool. If a student's servo is stuck, the color tells you which state the program thinks it is in, which usually points straight at the problem.

🧠Argue the Theory

Short discussion, and where the science practice standard gets earned.

Put the theory on the table: rhythmic movements could be generated by reflexes.
Ask students what in their simulation supports that idea, and what does not.
Ask what evidence they would want from a real body to decide. Let the question stay open.

Teaching tip: Take a disagreement if you get one. "Engaging in argument from evidence" means students defending a position with what they observed, not repeating a definition back to you.

✏️Wrap-up & Exit Ticket

Close on rhythms the body runs without asking.

Exit ticket: each student names a motion that is set by the CPG.
For a few of them, ask what could interrupt that rhythm and what would let it resume.
Collect the Activity Guides and have students return the servos and potentiometers.

Teaching tip: Walking, breathing, swimming, and chewing all count. If most of the room writes "chewing," push for one that was not in the program so you know they generalized.

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