Explain why the action potential moves in one direction
Three steps, the way the exam actually works: work through the lab, write down your own observations, then answer a 6-point free response. What you recorded goes to the grader with your writing, so a conclusion that does not follow from your own evidence will cost you the point — exactly as it would with a real reader.
Predict before you look
- The resting membrane potential is negative inside. Which ion sits concentrated OUTSIDE the cell and rushes in when its channels open?
- An action potential is all-or-nothing. What does that imply about how a neuron encodes the STRENGTH of a stimulus, if not by firing harder?
Nothing to submit here — these are to think through, so the prediction below is an informed one rather than a guess.
Commit to an answer now. It is not graded and being wrong costs nothing — the point is to have something specific to reconcile against once you have the data.
Answer every prediction to unlock the lab. A sentence is enough.
Run the investigation
Predictions first
The procedure and the simulation unlock once you have committed above. Observing before predicting is how a wrong intuition survives a lab intact.
Record what you found
This is your reading of the source, not ours. The grader sees them, so your conclusions have to follow from what you actually recorded.
| What characterizes the resting state | |
|---|---|
| What drives depolarization | |
| What drives repolarization | |
| What characterizes the refractory period |
Answer the free response
The lab shows neural firing as a sequence, not a single flash. (a) Explain how opening voltage-gated sodium channels produces the rising phase of the action potential. (b) Explain how repolarization and the refractory period keep the impulse moving in one direction rather than bouncing backward. (c) Distinguish an action potential from a graded potential in terms of amplitude and threshold behavior. (d) A student says stronger stimuli make “bigger” action potentials. Evaluate that claim and explain what really changes when stimulus strength increases.
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