Week 12 A&P Lab & Inquiry: Watch a Neuron Fire

Human Anatomy and Physiology I Free sample edition

Part 1 — The Big Picture

This week you learned how a neuron is built, why a resting neuron holds a charge with the inside negative, and how an action potential runs in a fixed order, with sodium rushing in to raise the spike and potassium flowing out to bring it back down. In this lab you stimulate a neuron in a free simulation, read its membrane potential from a chart at each phase, name the ion and the gated channel behind each move, and test whether a repeated stimulus makes a bigger spike. You define the variable so it can be measured, write a hypothesis before you start, and finish by checking a chatbot's account of your lab and catching its slips.

Time budget: Plan for about 120 minutes.

Part 2 — The Task

Guiding question: When a neuron fires, in what order does its membrane potential change, which ion and which gated channel drive each change, and does a repeated stimulus make a bigger spike?

Before you begin — hypothesis: Before you open the simulation, write one hypothesis in the if… then… because… form about stimulating a resting neuron: if you stimulate it, then the membrane potential will rise or fall first and the inside will become more positive or more negative, because of a reason about an ion that you can state. Then define your variable so it can be measured: name what you read from the chart and the unit it is measured in.

Workshop data: Your own readings from a free neuron simulation's potential chart, or the printed fallback readings

Source: Membrane-potential readings and observations you record yourself in the free Neuron simulation, following the procedure in Part 3; if the simulation will not run, the printed fallback readings, constructed for this lab as a stand-in and not recorded from the simulation, take their place.

Rows: 5 readings in the phase table, one per phase from rest back to rest, plus 3 rows in the repeat table, one per stimulus you try; the planning table has 4 rows that set up the hypothesis rather than data
Columns: phase, the membrane potential you read in mV, the ion and its direction, and which gated channel is open in the phase table; stimulus, the peak you read in mV, and whether the peak matched the first one in the repeat table
Unit: membrane potential in mV, read from the simulation's Membrane Potential (mV) axis, with the sign written every time

Part 3 — Materials & Procedure

Tools and materials

A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet)

Ways of working

structure-identification-on-a-virtual-atlas
histology-on-a-virtual-microscope
at-home-physiology-measurement-and-data-table

Procedure

Open the free Neuron simulation at https://phet.colorado.edu/en/simulations/neuron in a web browser and start it; no account is needed. Find the neuron's axon across the screen, the Stimulate Neuron button, and the check boxes for All Ions, Charges, Concentrations, and Potential Chart. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: The simulation is running and shows an axon with its membrane and a Stimulate Neuron button.
Check the Potential Chart and All Ions boxes, and set the speed to Slow Motion. Before you stimulate anything, read the line on the Membrane Potential (mV) axis and write the resting value, with its sign, in the Rest row of the phase table. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: The chart shows a flat line below zero, so the resting value you record carries a minus sign.
Press Stimulate Neuron once and watch the chart and the membrane together. Open the Legend if you need it to tell the Sodium Gated Channel from the Potassium Gated Channel. Record the highest value the line reaches, which ions cross the membrane, which way they move, and which gated channels are open, in the Depolarization row. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: The line climbs steeply above zero to a peak while the sodium gated channels open and sodium ions move into the axon.
Keep watching as the line falls. Record which gated channels open next and which ions cross, in which direction, in the Repolarization row; then record the lowest value the line reaches below rest in the Hyperpolarization row, and the value it settles back to in the Back to rest row. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: The line falls back below zero as potassium ions move out, dips briefly below the resting value, then settles near where it started.
Press Clear under the chart, then press Stimulate Neuron again and read the new peak; repeat once more. Record each peak in the repeat table and note whether it matched the first peak. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: Each stimulus that fires the neuron produces a peak of about the same height as the first.
Open a blank spreadsheet and type your resting value in cell B2 and your peak in cell B3, each with its sign. In cell B4 type the formula =B3-B2 to find the upstroke, and in cell B5 type =B2+70 to compare your resting reading with the course's conventional value of about −70 mV. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: Cell B4 returns a positive upstroke in mV, and cell B5 returns how far your resting reading sits from −70 mV, which may be zero or a few mV.

Fallback route

When to use it: Use this route if the Neuron simulation will not load on your device, or if you cannot use a computer for the simulation part of the lab.

Use the illustrative fallback readings below, constructed for this lab and not recorded from the simulation, to complete the phase table and the repeat table, then complete every analysis question and the critique step, and submit the same items for equal credit. Fill the ion-and-direction and gated-channel columns yourself from this week's chapter.

This route earns the same credit as the primary route.

Illustrative fallback readings, constructed for this lab, that stand in for your own simulation runs.

Fallback model data
Reading	Membrane potential (mV)	Ion and direction	Gated channel open
Rest	−68
Depolarization (peak)	+38
Repolarization (partway down)	−20
Hyperpolarization (lowest point)	−74
Back to rest	−68
Stimulus 2 peak	+38
Stimulus 3 peak	+38

Part 4 — The Scaffold

Name the parts of your inquiry before you start, so the reading is fair and the variable can be measured.

Student scaffold table 1
Part of the inquiry	Your answer
Hypothesis (if… then… because…)
The variable you read from the chart, and its unit
What you observe and record at each phase
One thing you keep the same for every stimulus

Record each phase in the order the chart shows it, so the order, the ions, and the values sit side by side.

Student scaffold table 2
Phase	Membrane potential you read (mV)	Ion and direction	Gated channel open
Rest
Depolarization (to the peak)
Repolarization
Hyperpolarization (lowest point)
Back to rest

Stimulate the neuron more than once, so you can test whether a spike ever comes out bigger.

Student scaffold table 3
Stimulus	Peak you read (mV)	Same height as the first peak?
Stimulus 1
Stimulus 2
Stimulus 3

Part 5 — Analysis Questions

Work the upstroke from your own resting value to your own peak as a signed difference, writing the subtraction of a negative as an addition, with its unit. Then find how far your resting reading sits from the course's conventional value of about −70 mV, and say whether that gap is large enough to matter.
Using your phase table, describe which gated channels opened first and which opened next, which ions crossed the membrane in each, and which way each ion moved. Did the line dip below your resting value before it settled?
Using your repeat table, explain what the all-or-none principle predicts about the three peaks and whether your readings support it. Then explain how a neuron could still signal a stronger stimulus if every spike is the same size.
Your simulated spike traveled along one stretch of axon. Explain what would change if that axon were wrapped in myelin with nodes of Ranvier, and what happens in order when the spike reaches the axon terminal and has to cross a synapse.
Answer one option. (a) The simulation is a model: name one way its chart could differ from a real neuron's membrane potential, and say why the model is still useful for learning the order of the phases. (b) You read your values from a chart by eye: name one way your readings could be off, and say how stimulating the neuron more than once helps you trust the pattern even if a single value is not exact.

Part 6 — AI-Critique Moment

Choose one equal-credit critique route. Route A: ask an approved AI tool to critique your completed work, then check its response against your own evidence. Route B is the no-AI equivalent printed below.

Approved tools: Claude, Gemini, ChatGPT, Grok, Microsoft Copilot.

Prompt to paste:

I've pasted my completed Watch a Neuron Fire tables above. In my lab, my illustrative readings from a neuron simulation's potential chart were a resting value of −68 mV and a peak of +38 mV. Please do six things. First, work out the size of the upstroke from my resting value to my peak, showing the arithmetic. Second, list the phases of an action potential in order from rest back to rest, giving the ion that moves and its direction in each phase. Third, tell me which protein makes the membrane potential rise so fast during the spike, and what the sodium-potassium pump does. Fourth, name the glial cell that wraps the myelin around an axon in a nerve that runs to a leg muscle. Fifth, say what is happening during depolarization, in terms of which ion crosses the membrane. Sixth, tell me the exact conduction speed of a myelinated human axon in meters per second, with a source.

Test the response for these likely failures:

Chatbots sometimes name the oligodendrocyte as the myelin maker for any axon, including one in a nerve that runs out to a leg muscle.
Chatbots often say the sodium-potassium pump pushes sodium in to make the spike rise, pairing the pump with the job of the gated channels.
Chatbots sometimes drop the minus sign on the resting value and subtract the two sizes, giving a much smaller or even negative upstroke instead of the signed difference.
Chatbots sometimes list hyperpolarization before repolarization, or put the dip below rest at the start of the spike.
Chatbots sometimes describe depolarization as potassium leaving the cell, swapping the two phases' names and ions.
Chatbots readily supply an exact conduction speed in meters per second for a myelinated axon, with a confident citation this lab never gave.

In 3–4 sentences, name what the chatbot got right, quote at least two of its errors, and correct each one with evidence from your tables or the chapter.

Equivalent route (no AI required)

No AI account is required for this lab. Instead of the chatbot, critique this flawed analysis, printed here in full: "In my lab the resting value was −68 mV and the peak was +38 mV, so the upstroke was 38 + 68 = 96 mV. The sodium-potassium pump pushed sodium into the axon to make the spike rise. During depolarization, potassium left the cell. The phases ran rest, hyperpolarization, depolarization, repolarization, rest. The axon in a nerve running to my calf muscle was wrapped by an oligodendrocyte. A myelinated human axon conducts at exactly 95 meters per second, as studies show." Mark it up: quote each flawed sentence, name what is wrong (a mislabeled structure, a wrong structure-to-function pairing, a miscomputed value, an order scrambled, a confused phase name, or an invented figure), cite the evidence from your tables or this week's chapter, and write a corrected sentence beneath it. This route assesses the same objectives (Objective 6 and Objective 2) as the chatbot critique, takes comparable effort (about 30 minutes and 200–300 words), is scored by the same scoring criteria for the same credit, and its own submission artifact is the marked-up flawed analysis, posted in place of the chatbot share link and report.

Part 7 — What to Submit

All three completed scaffold tables, with the phase and repeat tables filled from your own simulation runs or the illustrative fallback readings
Written answers to all five analysis questions, including the option you chose for question 5
The chatbot critique report with its share link, or the equivalent route's marked-up flawed analysis

Deliverable:

A short A&P Lab & Inquiry report on watching a neuron fire: three completed tables (the parts of your inquiry, the five-phase table, and the three-stimulus repeat table), written answers to five analysis questions, and a critique of a chatbot's account of your lab, or, on the equivalent route, a marked-up correction of the printed flawed analysis. 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. Choose a written, recorded, or visual form for your answers; every form is graded by the same scoring criteria.

Rubric

The rubric below shows how each submitted part is evaluated; bands are full, partial, or none.

Workshop evaluation criteria
Criterion	Full	Partial	None
Testable hypothesis and a measurable variable	A falsifiable if… then… because… hypothesis appears before the simulation, the chart reading is named as the variable with its unit, and one condition held the same is named.	A hypothesis appears but is not falsifiable, or the variable or its unit is missing.	No hypothesis, and the parts of the inquiry are not named.
Phase table	All five phases are recorded in order from the student's own runs or the fallback readings, each with a signed value in mV, the ion and its direction, and the gated channel, with sodium in for depolarization and potassium out for repolarization.	Most phases are recorded, but a sign is missing, a phase is out of order, or an ion or direction is swapped in one row.	The phase table is blank, or it is not based on the simulation or the fallback.
Repeat stimuli and the all-or-none test	Three peaks are recorded and compared, and the comparison is used to judge whether a repeated stimulus made a bigger spike.	Peaks are recorded but not compared, or only one repeat is tried.	The repeat table is blank.
Analysis and the mechanism in your own words	Answers all five questions with evidence from the tables: the signed upstroke and the gap from −70 mV, the channel and ion sequence, the all-or-none reading of the peaks, the myelin and synapse steps in order, and one chosen limitation option.	Answers most questions but leaves one unsupported, or states the mechanism without tying it to the tables.	Analysis questions are unanswered or unsupported by the tables.
Critique of the chatbot or of the printed flawed analysis	On either route, at least two errors are quoted and corrected with evidence from the student's own tables or the chapter, and one correct point is acknowledged; both routes earn this band equally.	On either route, errors are named but corrected without evidence, or only one error is caught.	No critique appears, or pasted output is submitted without any checking.

Quality Gate

Every row of the phase table carries a value with its sign and unit, the ion and its direction, and the gated channel, in the order the chart showed them.
Depolarization is tied to sodium moving in and repolarization to potassium moving out, never the reverse.
The hypothesis was written before the simulation and has the if… then… because… form, and the variable is defined so it can be measured.
The phase and repeat tables come from your own runs or the printed fallback readings, never from memory or a chatbot.
No measurement, conduction speed, concentration, study, or source is invented anywhere in the submission.
The critique quotes the chatbot or the flawed analysis and corrects at least two errors with evidence from your tables or the chapter.

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