Action Potential Quiz: 15 Questions With Answers
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A neuron fires an action potential when voltage-gated sodium channels open at threshold, causing rapid depolarization; potassium channels then repolarize. Myelination enables saltatory conduction for fast, efficient signaling.
This quiz covers the fundamentals of the neuronal action potential, from resting membrane potential to saltatory conduction. It's designed for students of neuroscience, physiology, or biology who want to test their understanding of how neurons generate and propagate electrical signals.
Before starting, remember the key sequence: a stimulus depolarizes the membrane to threshold, opening voltage-gated Na+ channels; Na+ influx drives the upstroke, then Na+ channels inactivate and K+ channels open, restoring the resting potential. Refractory periods ensure one-way propagation.
The questions
What is the typical resting membrane potential of a neuron?
Which ion is most permeable at the resting membrane potential?
What happens when the membrane potential reaches threshold?
Which event causes the rapid depolarization phase of the action potential?
During repolarization, which ion moves out of the neuron?
What is the main cause of the absolute refractory period?
During the relative refractory period, a neuron can fire again if the stimulus is?
In a myelinated axon, where are voltage-gated Na+ channels concentrated?
What is the primary advantage of saltatory conduction?
The Na+/K+ ATPase pump moves which ions in which directions?
Which statement about voltage-gated Na+ channels is correct?
If a stimulus is below threshold, what happens?
What causes the brief hyperpolarization (undershoot) after an action potential?
How does action potential amplitude change as stimulus strength increases above threshold?
Which sequence correctly orders events during the action potential?
0 of 15 answered · 0 correct
Cheat sheet: key terms
| Resting potential | Membrane voltage around -70 mV, maintained by K+ leak channels and Na+/K+ pump. |
|---|---|
| Threshold | About -55 mV; voltage at which voltage-gated Na+ channels open and action potential fires. |
| Depolarization | Rapid Na+ influx through voltage-gated Na+ channels makes membrane more positive. |
| Repolarization | Na+ channels inactivate; voltage-gated K+ channels open, K+ efflux restores negative membrane. |
| Absolute refractory period | Na+ channels inactivated, so no stimulus can trigger another action potential. |
| Relative refractory period | Some Na+ channels recovered but K+ conductance high; stronger-than-normal stimulus needed. |
| Saltatory conduction | Action potential jumps between nodes of Ranvier in myelinated axons, increasing speed and efficiency. |
Answers explained
Show all 15 answers
- What is the typical resting membrane potential of a neuron? -70 mV. Resting potential is set mainly by potassium leak channels, making the inside negative relative to outside.
- Which ion is most permeable at the resting membrane potential? Potassium (K+). Resting membranes have many more open potassium leak channels than sodium channels, so K+ dominates permeability.
- What happens when the membrane potential reaches threshold? Voltage-gated Na+ channels open. Threshold is the voltage at which voltage-gated sodium channels open, initiating the action potential.
- Which event causes the rapid depolarization phase of the action potential? Na+ influx through voltage-gated Na+ channels. Sodium influx makes the membrane more positive, driving depolarization from around -70 mV toward +30 mV.
- During repolarization, which ion moves out of the neuron? Potassium (K+). Voltage-gated K+ channels open after a delay, and potassium efflux returns the membrane potential toward resting level.
- What is the main cause of the absolute refractory period? Inactivation of voltage-gated Na+ channels. After depolarization, Na+ channels enter an inactivated state and cannot reopen until the membrane repolarizes, preventing another action potential.
- During the relative refractory period, a neuron can fire again if the stimulus is? Stronger than normal. Some Na+ channels have recovered, but K+ conductance remains high, so a larger depolarization is needed to reach threshold.
- In a myelinated axon, where are voltage-gated Na+ channels concentrated? Nodes of Ranvier. Myelin insulates the axon, so Na+ channels are clustered at exposed nodes of Ranvier, allowing saltatory conduction.
- What is the primary advantage of saltatory conduction? Faster and more energy-efficient propagation. By jumping between nodes, action potentials travel much faster and require less active ion pumping than in unmyelinated axons.
- The Na+/K+ ATPase pump moves which ions in which directions? 3 Na+ out, 2 K+ in. The pump uses ATP to export three sodium ions and import two potassium ions per cycle, maintaining concentration gradients.
- Which statement about voltage-gated Na+ channels is correct? They open rapidly and then inactivate within milliseconds. Na+ channels have an activation gate that opens quickly and an inactivation gate that closes shortly after, terminating Na+ influx.
- If a stimulus is below threshold, what happens? A small local depolarization that decays with distance. Subthreshold stimuli cause passive electrotonic potentials that do not trigger regenerative Na+ channel opening, so they die out.
- What causes the brief hyperpolarization (undershoot) after an action potential? Slow closure of voltage-gated K+ channels. Potassium channels remain open after the membrane reaches rest, allowing excess K+ to leave and making the inside more negative than normal.
- How does action potential amplitude change as stimulus strength increases above threshold? It stays the same (all-or-none). Once threshold is reached, the action potential is a fixed-size event; stimulus strength affects firing frequency, not amplitude.
- Which sequence correctly orders events during the action potential? Depolarization → repolarization → hyperpolarization. First Na+ influx depolarizes, then K+ efflux repolarizes, and continued K+ efflux briefly hyperpolarizes before returning to resting potential.
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