Week 10 Discussion — Combs, Dominoes, and a Hand That Slows Down — Traditional alternative (no AI)
Instructors: publish this instead of the adaptive version if you prefer, and unpublish or delete the adaptive one.
Hook
Squeeze a tennis ball for five rounds and the count falls: in the course's illustrative grip-fatigue series it drops from 24 squeezes to 12, a 50% decline. Yet not one filament in that hand got shorter, and even letting go of the ball cost the fibers energy.
Your discussion question — choose Option A or Option B; they carry the same weight and the same rubric, and you say which you picked.
Option A: This week taught contraction with a classroom picture: two combs whose teeth slide into more overlap while no tooth gets shorter. Argue whether that comb picture helps or misleads a beginner about what really happens in a muscle fiber, using the sarcomere, the Z discs, the A band, the cross-bridges, and ATP, and tie it to a moment from your own life such as carrying groceries, opening a stubborn jar, or a long walk. Then make the best case for the side you did not take.
Option B: Many people think of relaxing a muscle as no more than stopping, a moment of doing nothing. Using this week's ordered relaxation steps, the ATP-powered calcium pumps, and rigor mortis, argue whether "relaxation" is a good name for what a muscle fiber actually does when it stops contracting, or whether another word would teach it better. Then name the strongest case for the other view.
There is no single right answer here. Two careful people can judge the comb picture or the word "relaxation" differently. Pick the option you care about, and walk us through your reasoning.
Expectations
Activity format: one initial post followed by two substantive peer replies. Plan on about 45 minutes across the two deadlines; your instructor sets both due dates in Canvas.
Your initial post — by the first due date (early in the module week):
- Say which option you chose.
- For Option A, say whether the comb picture helps or misleads, name the sarcomere, the Z discs, the A band, the cross-bridges, and ATP, and tie it to a moment from your own life; for Option B, say whether "relaxation" is a good name, walk through the four relaxation steps in order, and say where ATP is spent.
- Use at least two of this week's terms (sarcomere, actin, myosin, cross-bridge, power stroke, sarcoplasmic reticulum, relaxation, rigor mortis) correctly.
- Say what idea or observation would change your mind.
- Length: roughly 150–250 words if written. You may instead record your post as audio or video (about two minutes) and attach a transcript; both forms are scored by the same rubric.
Your replies — by the second due date (the end of the module week):
- Reply substantively to at least two classmates.
- A substantive reply does more than agree: make the case for the other side, point out where a post said the filaments shorten or called actin the thick filament, or ask which relaxation step a post left out. "Nice point!" on its own does not count.
What a strong post looks like:
I chose Option A, and I think the comb picture helps more than it misleads. When I open a stubborn jar, my forearm muscles shorten, but the comb picture reminds me that no filament gets shorter: the thin actin filaments are pulled past the thick myosin filaments, the Z discs move closer, and the A band keeps its width. The best case against me is that combs do not grab, pull, and let go, so the picture hides the cross-bridges and the ATP each power stroke and each release needs. I would change my mind if beginners using the comb picture forgot that ATP is spent at every step.
Notice how it takes a side, names the structures and what each does, ties it to a real moment, and takes the strongest objection seriously. That is the bar.
Participation rubric
This discussion is worth 10 points. The three criteria below look at your initial post and your peer replies.
| Criterion | Full credit | Partial credit | No credit |
|---|---|---|---|
| Quality of the initial post (4 pts) | A clear position built on a mechanism: filaments sliding within a sarcomere traced to the Z discs and the A band, or relaxation traced step by step to the ATP-powered calcium pumps | A position is stated, but the mechanism is skipped or the life moment is vague | Missing, off-topic, or no reasoning about sliding filaments or relaxation |
| Use of course concepts (3 pts) | Uses sarcomere, actin, myosin, cross-bridge, power stroke, sarcoplasmic reticulum, and relaxation precisely, each with its job | Uses a term loosely, or swaps a pair such as actin and myosin | No course terms, or used incorrectly |
| Engagement with peers (3 pts) | Two or more substantive replies that extend or challenge a classmate's reasoning | One substantive reply, or replies that only agree | No replies, or agreement with nothing added |
Post early if you can; the best threads happen when people have time to reply before the second due date.
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