Week 12 — Signed Steps and a Ruler Drop: A Nerve Impulse Report

Assignment 11 of the term — work the action potential's two signed differences, average a ruler drop, put the spike and the synapse in order, and explain to someone new why losing myelin slows a signal.

This adaptive assignment uses a coaching dialogue to help you turn a first attempt into a clear, evidence-based report. You stay the author: the coach asks questions, checks the reasoning you show, and waits for you to revise before it writes its report. Week 3 gave you the sodium-potassium pump and the difference between passive and active transport, and Week 10 showed a motor neuron releasing acetylcholine at the neuromuscular junction; this week you open the neuron itself. This week's lecture tutorial, quiz, discussion, and A&P Lab & Inquiry work the same ideas from other angles; this assignment is where you put them together.

The task

This week's shared datasets are Dataset I, the action-potential values (conventional approximations: rest about −70 mV, threshold about −55 mV, peak about +30 mV), and Dataset J, the ruler drop (illustrative: five catches of 18, 22, 19, 21, and 20 cm). The spike runs rest → depolarization (Na⁺ in) → repolarization (K⁺ out) → hyperpolarization → rest, and a synapse runs action potential at the terminal → Ca²⁺ in → neurotransmitter released → neurotransmitter binds the next cell.

Work these four problems, showing your arithmetic:

1. A neuron rests at −70 mV and reaches threshold at −55 mV. How large is the rise from rest to threshold, in mV?
2. The same neuron climbs from rest at −70 mV to a peak of +30 mV. How large is the upstroke, in mV?
3. In the ruler drop, five catches land at 18, 22, 19, 21, and 20 cm. What is the sum of the five catches, in cm?
4. Using that sum, what is the average catch distance, in cm?

Beside each answer, add one brief interpretation:

• Problem 1: name the channels that open at threshold, and say which ion moves and in which direction once they open.
• Problem 2: name the phase that follows the peak with its ion and direction, and name the brief phase that comes after it.
• Problem 3: name the links in the chain a ruler catch measures, and put the four steps at one synapse along that chain in order.
• Problem 4: say in words about how long a 20 cm catch takes, and explain whether a longer average distance would mean a faster or a slower chain.

Explain it to a non-expert

A friend reads that a disease which strips myelin from nerve fibers in the brain and spinal cord can slow or block signals, and asks, "Why would losing a wrapping slow a signal down? Isn't the nerve still there?" Write a 3–5 sentence message that explains, in everyday words, what myelin is and which cells make it, how the signal jumps from gap to gap along a wrapped fiber, and why losing the wrapping slows or blocks the jumps. Name one limit, for example that this course describes speeds only in words, or that this message is about how nerves work and not about anyone's health. Put any technical term in everyday words. More than one good message is possible.

For a different, ungraded example, imagine a friend who asks why a neuron at rest still holds a charge. Model answer: "Think of a phone battery sitting in a drawer: it is not doing anything, but it is ready. A resting nerve cell is like that, sitting at about minus 70 millivolts, with the inside more negative than the outside. A pump in its outer layer keeps more sodium outside and more potassium inside, and that uneven spread is the stored charge. The battery is only a classroom picture, and it leaves out how the charge is spent when the cell fires."

Use that pattern for the message to your friend, with your own wording and evidence.

Part 1 — Student instructions

1. Draft all four answers, the four brief interpretations, and your message to your friend before you open a chatbot.
2. Open any course-approved chatbot. Copy the entire Coach Prompt box, including its first and last marker lines, and paste it as one message. The coach asks for your draft and then works one question at a time.
3. Answer in your own words. Show calculations when asked. Use the coach's feedback to revise at least one calculation or explanation, even if your first attempt was correct.
4. Keep going until the prompt's exit condition is met.
5. Save the chat's share link and copy the final report exactly as the coach gives it.

The chatbot is a coach, not a ghostwriter. It draws out your reasoning; it does not write the report for you.

Coach Prompt

COPY EVERYTHING BELOW THIS LINE
ROLE: You are a careful learning coach for a first-semester anatomy and physiology course. Draw out and challenge MY thinking about the neuron and the nerve impulse. Do not write my assignment for me and do not invent work I never did. Never invent a measurement, a study, a conduction speed, or an ion concentration, and never offer medical advice or comment on anyone's health.

ASSIGNMENT: Work through these four problems in order, one at a time. Do not invent, replace, or reorder a problem. The data: Dataset I, the action-potential values (rest about −70 mV, threshold about −55 mV, peak about +30 mV; a negative value carries its minus sign), and Dataset J, the ruler drop (illustrative catches of 18, 22, 19, 21, and 20 cm). The spike runs rest -> depolarization (Na+ in) -> repolarization (K+ out) -> hyperpolarization -> rest. At a synapse: the action potential reaches the terminal -> Ca2+ flows in -> vesicles release neurotransmitter by exocytosis -> it crosses the cleft and binds receptors on the next cell. Oligodendrocytes make myelin in the brain and spinal cord; Schwann cells make it outside them; on a myelinated axon the signal jumps node to node.
PROBLEM P1: A neuron rests at −70 mV and reaches threshold at −55 mV. How large is the rise from rest to threshold, in mV?
PROBLEM P2: The same neuron climbs from rest at −70 mV to a peak of +30 mV. How large is the upstroke, in mV?
PROBLEM P3: In the ruler drop, five catches land at 18, 22, 19, 21, and 20 cm. What is the sum of the five catches, in cm?
PROBLEM P4: Using that sum, what is the average catch distance, in cm?
After the four answers, I must briefly interpret each one: for P1, name the channels that open at threshold and say which ion moves and in which direction; for P2, name the phase that follows the peak with its ion and direction, and name the brief phase after it; for P3, name the links in the chain a ruler catch measures and put the four synapse steps in order; for P4, say in words about how long a 20 cm catch takes and whether a longer average distance means a faster or a slower chain. I must then write a 3-5 sentence message to a friend explaining what myelin is and which cells make it, how the signal jumps from gap to gap, why losing the wrapping slows or blocks the jumps, and one limit. I must explain technical terms in everyday words.

SCORING CRITERIA: Score only evidence I supply: correct computations (40 points), nerve-impulse reasoning (32 points), clarity for a non-expert reader (16 points), and showing work so it can be checked (12 points). For each of P1-P4, give 2, 1, or 0 evidence units per criterion; one unit is worth 5 computation points, 4 reasoning points, 2 clarity points, or 1.5 showing-work points. Sum the four problems within each criterion. Count my friend message only with P4, for reasoning and for clarity.
COMPUTATION UNITS: A correct value with its unit in any equivalent notation = 2; the right numbers and operation with one arithmetic or sign slip = 1; a missing value or a wrong operation = 0.
REASONING UNITS: For each problem, an interpretation that covers both named parts = 2; one accurate part = 1; none = 0. Calling depolarization potassium leaving, giving the resting potential a plus sign, putting the phases out of order, saying myelin slows the signal, or saying a spark crosses the synapse is not accurate. An arithmetic slip alone is not a reasoning error.
CLARITY UNITS: For each problem, labeled evidence a newcomer can follow, with terms in everyday words = 2; evidence that needs a reread because of an unclear label or unexplained term = 1; no readable evidence = 0. Include my friend message with P4. Missing reasoning alone does not lower clarity for otherwise clear work.
SHOWING-WORK UNITS: For each problem, numbers and steps that let a reader rebuild the value = 2; one relevant but incomplete number or step = 1; a bare result or no method = 0. A visible method stays checkable despite an arithmetic slip.

Do NOT invent grading rules.

DIALOGUE RULES: Ask exactly one question per message and wait for my answer. Start by asking for my complete first attempt. Build each next question from my exact words. Probe an unsupported claim and ask me what supports it. Keep the conversation on questions, not on finished work.

ENGAGEMENT GUARDS: A greeting, a copied prompt, a yes/no reply, or a one-word answer is not a substantive exchange. Do not flatter or treat agreement as evidence. Praise only a concrete move I made. If evidence is missing, say what is missing and ask for it. Require a real revision plus a short reflection on why the revision is better. Never score evidence I did not supply, and do not issue the report early.

EXIT CONDITION: Continue until at least five substantive exchanges have occurred AND I have supplied all four answers and their brief interpretations AND written my message to my friend AND revised at least one calculation or explanation AND reflected on the revision. Stop only after whichever requirement happens last.

REPORT: After the exit condition is satisfied, output exactly these labelled lines in this order. Replace X with the exact earned score; it may end in .5 and must not be rounded. Base every line only on evidence in this chat; write "Not supplied" for missing evidence and never raise the score for polished chatbot prose.
STUDENT'S SCORE: X/100
EVIDENCE FOR THE SCORE: [specific evidence from my values and reasoning]
REVISION MADE: [what I changed and why]
STRENGTH: [one earned strength]
NEXT STEP: [one concrete improvement]
Then tell me to submit this report, my revised Week 12 nerve impulse report, and the share link.
COPY EVERYTHING ABOVE THIS LINE

Deliverables

Submit these three items in the assignment entry:

• your revised Week 12 nerve impulse report with all four answers, their brief interpretations, and your message to your friend — written, or recorded as audio or video with a transcript, or as a labeled sketch of one action potential with its phases and ions and a short note; every form is graded by the same scoring criteria;
• the coach's five-line report; and
• the conversation share link.

Submit in any accessible file type or as a link; a recorded response may be submitted as audio or video with a transcript, or as text.

Equivalent route (no AI required)

This route assesses the same Week 12 skills — working signed differences in mV, averaging a ruler drop, putting the spike and the synapse in order with their ions, and explaining myelin in plain words — for comparable time and effort, about 60 to 90 minutes, the same as the coached route. Complete the same four problems, the four brief interpretations, and the message to your friend. Then audit your own first draft against the attached scoring criteria, one criterion at a time, and write a second draft. Add a 150–200 word revision memo that names one value or explanation you changed, the evidence that prompted the change, and one question you still have. Submit the revised report, your completed criteria checklist, and the revision memo in the assignment entry; together they replace the share link and the coach's report. This route uses the same scoring criteria and the same points, with no penalty for choosing it.

How you'll be graded

The full analytic rubric is attached to this assignment in Canvas.

Academic integrity and AI use

The values, reasoning, revision, and final report must be your own. Do not ask the chatbot to create the assignment or to add evidence you did not produce. Submit an honest share link from your own dialogue. The equivalent route keeps the same workload and evidence and needs no AI account.

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