Unit 6.6: Lesson 2
PIRL EXPERIMENTAL / OPENSCIED IN MY CLASSROOM · UNIT 6.6
From movement to injury: how subsystems work together
Three days of arm models, injury simulations, and notebook work—and what I will change next time.
This was supposed to be an alternative to a lesson I already knew how to teach well. It became a three-day investigation into movement and injury—and a useful reminder that an activity can have a place without doing everything I hoped it would do.
The sequence grew out of OpenSciEd Unit 6.6’s Lesson 2 chicken-wing dissection. In my classroom, I use frog legs. I have that activity down pat, and it is an awesome kickoff for exploring how muscles, tendons, and bones work together. This time, I tried an alternative built around a Carolina Biological arm model, rubber bands, simulations, and a review of skin, muscle, and bone.
There were useful pieces. There were also parts I would change substantially. Next time, the frog-leg dissection is coming back.
Day 1: What can an arm model actually explain?
I wanted students thinking about an arm as a system of interacting parts. Naming a muscle or a bone was only a starting point. The more useful question was how those parts affect one another—and how their structure helps them do their jobs.
My notebook began with a simple whole-to-parts sketch. A system contains subsystems, and those parts interact: they work together and affect each other. That idea would carry through both notebook spreads.
Before treating the model as an explanation, we considered its materials. What are the strengths and limitations of using bubble wrap for skin, string or rubber bands for muscle, and wood for bone?
That question matters because different materials reveal different features. Wood can represent a firm supporting structure. A piece of rope can show smaller strands bundled together. A stretched rubber band can pull on the arm. None of those materials behaves exactly like living tissue.
The investigation moved from identifying parts to comparing materials, observing opposing pulls, and using observations to explain movement. Students matched the wooden pieces and hinge to parts of an arm, examined smaller strands in different strings, and considered what each material showed well or left out.
I also wanted them to support their explanations with something they had actually observed. “This represents a muscle” is less useful than explaining which feature makes it a useful muscle model—and which feature makes the comparison break down.
Day 2: Changing the pulls—and reconsidering the measurements
The rubber bands were the strongest part of the physical model experience. Changing the bands on opposite sides of the joint made the effect of competing pulls visible. Students could watch the forearm move and notice what happened to the other band as the position changed.
My notebook records the changes directly: more bands at A–B moved the forearm upward; more at E–F moved it downward. I sketched the positions, recorded the band combinations, and wrote questions about what the results meant.
One of those questions was whether needing two bands on one side to balance one on the other meant something about real biceps and triceps. That is exactly where I need students to examine the model’s limits. Band stretch, attachment position, and the joint all influence the result. A band count in this setup does not establish a strength ratio for human muscles.
The spring-scale data collection was not worth the time in this version. The scales I was using were not sensitive enough to distinguish the smaller forces clearly. I was hoping for measurements that would help students compare setups. Instead, the equipment made those comparisons harder to interpret.
Those scales may have a better role with larger forces—more rubber bands or heavier loads, within the equipment’s limits. That would be something to check before building another investigation around it. For the low-force setup I tried, the measurements did not give us the useful evidence I wanted.
The arm model still earned a place. I would use it for a focused engagement activity or when connecting muscle structure to pulling force. With similar bands stretched in comparable ways, adding bands can increase the pull. It also makes opposing tension easy to see.
The limitation needs to stay visible: rubber bands pull because they are stretched, while living muscles actively contract. The model helps us reason about pulls and connections. It gives us a partial explanation of a real arm.
The injury simulation made the connections more useful
The simulation that particularly helped was my Muscle, Bone & Movement simulation. Students could change the condition of the muscle, tendon, or upper-arm bone and compare the resulting movement.
This served a different purpose from the simpler Muscles Work in Pairs simulation. The injury model let us ask what happens when one part of the connected system can no longer do its job effectively.
I went through that work myself. My notebook used an Injury / Notice / Wonder organizer: record the condition, describe what changes in the model, and ask a question the observation raises. I felt students got quite a bit out of this part.
The useful connection was that a muscle’s pull depends on other structures. If the muscle produces less effective force, movement can change. If the tendon connection is damaged, that pull may not transfer effectively to the bone. If the supporting bone is broken, the system may move differently even when the muscle still pulls.
The questions in my notebook went beyond naming the injury: What exactly is a muscle strain? What happens when a connection tears? Could a broken bone affect nearby tissue? We did not need to answer every question immediately. The observations gave us a reason to keep learning about the structures.
The simulation was useful, but it was no substitute for the dissection. It presents selected relationships clearly. The dissection lets students encounter the actual structures and connections we are trying to explain. I want both experiences in the next version.
Day 3: What happens when a subsystem breaks?
INB pages 18–19 broadened the focus to skin, muscle, and bone. We returned to structure and function, then used those relationships to predict what an injury might change.
The organizer had four columns: Structure (Look), Function (Job), Predict, and Revise/Refine. Skin, muscle, and bone each had a row. The arrows between structure and function helped make the connections explicit.
We connected skin’s outer covering and layers with protection, its flexibility with movement, and the nerves in skin with sensation. We connected muscle fibers and tendons with pulling and movement. Bone’s rigidity connected to shape, support, and protection.
Students then made at least one prediction for each injured subsystem. The point was to reason from the structure and its job. If that part changes, what function might change with it?
Operation Ouch supported the revise-and-refine step
I really like Operation Ouch for bringing body structures and injuries into a concrete context. For this lesson, I used the following videos. These links let you preview the originals and choose what fits your class:
Students returned to their predictions while watching. Revise meant change an idea. Refine meant add useful detail. A prediction could be reasonable and still benefit from a more complete explanation.
The completed spread shows how the ideas accumulated. My notes connect injury with changes in protection, sensation, movement, and support. They also show how a problem in one part can involve other nearby structures.
Honestly, this review was a little boring. It was also effective at reviewing and applying information. Both things can be true. Repeating the same routine across several subsystems helped organize the thinking, but it also made the lesson feel repetitive.
Next time, I would keep the organizer and shorten the review. I would have students retrieve more of the initial structure-and-function connections, choose a few predictions worth discussing, and focus our conversation on what changed: “What did you revise, and what information made you revise it?”
Bringing the three days together
The two progress-tracker entries capture the larger progression. First: “Subsystems work together…” Then: “When a subsystem breaks…” The second explanation should build on the first.
I want students to explain a chain of effects. A muscle pulls through a tendon on a bone, helping produce movement at a joint. Damage to one of those structures can change the resulting movement. Skin adds another part of the story through protection, flexibility, and sensation.
The goal is never simply to copy my notebook. I want students using their own observations to explain what they understand, then making corrections and additions that help them study later. The notebook should preserve the development of their thinking.
The companion assessment is evolving in the same direction. Injury situations can ask students to evaluate claims, interpret observations, and decide what the evidence does or does not establish. That tells me more than asking them to name a tendon.
Why the frog-leg dissection is coming back
My earlier dissection deck makes the missing experience clear. It provides a visual plan for exposing the structures, observing how a pull produces movement, and then comparing that movement after a bone is damaged. This is the established lesson I want to restore; it was not an additional activity completed during this year’s three-day alternative.
Viewer discretion: the following images show a frog-leg dissection. These stills come from my visual instructional slides. The dissection recording linked in the deck provides the video resource; access depends on its sharing settings.
The sequence begins by removing the skin to reveal the structures underneath. The important observation comes when the calf is freed at its upper end while the tendon connection at the ankle remains. Students can see actual tissue connections rather than having to imagine what a rubber band stands for.
Then we apply a pull to the freed end of the calf and observe the foot. The specimen does not actively contract; our external pull demonstrates how force can travel through the connected structures and produce movement. That distinction also helps students compare this experience with the rubber-band arm.
The plan then introduces a break in the shin and repeats the movement test. Students compare the system before and after the structural change. The question becomes: Why does the same kind of pull now produce a different result?
That comparison is why I value this activity so much. The model and simulation can help students isolate relationships and repeat trials. The dissection grounds those relationships in actual structures. My original classroom guidance also makes space for students to opt out without penalty or judgment.
What stays—and what changes next time
The frog-leg dissection returns as the kickoff. It is an activity I know well, and it gives students a concrete experience with real structures to revisit throughout the sequence.
I will keep the Carolina arm for a narrower purpose: opposing pulls, connections, and possibly the relationship between band number and force. I will test the measuring equipment before asking students to spend time collecting force data. If the scales cannot resolve the differences we are investigating, the activity needs different equipment or a different question.
I will keep the injury simulation and the Notice/Wonder work. That was a useful bridge between movement and what happens when a part is damaged. I will also keep Operation Ouch and the predict–revise routine, while tightening the review.
The first version was uncomfortable. I put pressure on myself to have it figured out, even while teaching it for the first time. Looking across all three days helps me see the useful learning and the changes the lesson still needs.
I often remind parents that middle-school standards describe what students should be able to do by the end of grade eight. I needed some of that longer-term perspective myself. Students’ understanding—and my teaching of this sequence—will develop over more than one lesson.
This version helped clarify what each experience contributes. The next version can build on that. Experiment. Learn. Refine.
