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.
Run the investigation
- 1Step through the resting, depolarization, repolarization, and refractory phases in the lab.
- 2Record what happens to sodium and potassium channel activity in each phase.
- 3Identify when the membrane potential rises most steeply and when it undershoots resting potential.
- 4Use the sequence to explain why a second impulse cannot immediately start in the same segment.
Booting the lab…
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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