Anatomy Quiz: Neuron Structure And Action Potentials
20 questions · exam conditions
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Neuron Structure And Action PotentialsQuestion 1 of 20

A neuron's resting membrane potential is maintained at -70 mV. If the sodium-potassium pump suddenly stops functioning while passive leak channels remain open, what will be the most likely sequence of events over the next several minutes?

The membrane will immediately depolarize to 0 mV, then gradually hyperpolarize as potassium continues to leak out
The membrane will gradually depolarize toward 0 mV as sodium leaks in faster than potassium leaks out, eventually reaching electrochemical equilibrium
The membrane potential will remain stable at -70 mV because leak channels maintain the resting potential independently
The membrane will hyperpolarize further as potassium accumulates outside the cell and sodium accumulates inside the cell
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Anatomy Quiz

Anatomy Quiz: Neuron Structure And Action Potentials

Practice Neuron Structure And Action Potentials in Anatomy with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Neuron Structure And Action Potentials, giving you a quick way to practice the rules, question types, and explanations that matter most for Anatomy.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

A neuron's resting membrane potential is maintained at -70 mV. If the sodium-potassium pump suddenly stops functioning while passive leak channels remain open, what will be the most likely sequence of events over the next several minutes?

  1. The membrane will immediately depolarize to 0 mV, then gradually hyperpolarize as potassium continues to leak out
  2. The membrane will gradually depolarize toward 0 mV as sodium leaks in faster than potassium leaks out, eventually reaching electrochemical equilibrium (correct answer)
  3. The membrane potential will remain stable at -70 mV because leak channels maintain the resting potential independently
  4. The membrane will hyperpolarize further as potassium accumulates outside the cell and sodium accumulates inside the cell
Explanation: Without the sodium-potassium pump actively transporting Na+ out and K+ in, the membrane potential will gradually drift toward 0 mV due to passive ion movement through leak channels. Since sodium leak channels allow Na+ to enter down its concentration gradient faster than K+ exits, net depolarization occurs until electrochemical equilibrium is reached. Choice A is incorrect because immediate depolarization to 0 mV wouldn't occur, and subsequent hyperpolarization wouldn't happen with a non-functioning pump. Choice C is wrong because leak channels alone cannot maintain resting potential without active transport. Choice D is incorrect because K+ accumulating outside would actually cause depolarization, not hyperpolarization.

Question 2

Scenario—Action Potential Process: In an A&P lab, a neuron rests at −70 mV due to Na+/K+ gradients. When a stimulus reaches threshold at the axon hillock, voltage-gated Na+ channels open causing rapid depolarization; then Na+ channels inactivate and voltage-gated K+ channels open, producing repolarization and brief hyperpolarization before returning to resting potential. How do ion channels regulate depolarization, repolarization, and hyperpolarization?

Neuron structure context: dendrites receive input, the soma integrates signals, and the axon conducts action potentials to axon terminals.

Diagram (text-only): [Dendrites] → (Soma) → [Axon hillock] ======= Axon =======> [Axon terminals]

Question: What occurs during the depolarization phase of an action potential?

  1. Voltage-gated K+ channels open, and K+ exits the cell
  2. Voltage-gated Na+ channels open, and Na+ enters the cell (correct answer)
  3. Ligand-gated Cl− channels open, and Cl− enters the cell
  4. Na+/K+ pumps stop, and ions diffuse freely
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies Na+ influx through voltage-gated Na+ channels as playing a key role in depolarization, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that K+ efflux occurs during depolarization, which reflects a misunderstanding of the sequence in action potential phases. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 3

Scenario—Neuron Anatomy: A typical multipolar neuron has dendrites that receive synaptic input, a soma (cell body) containing the nucleus that integrates incoming graded signals, and a single axon that begins at the axon hillock and conducts action potentials toward axon terminals.

Diagram (text-only): Dendrites / |
( Soma )—Axon hillock—========== Axon ==========> Terminals

Action potential context: reaching threshold at the hillock opens voltage-gated Na+ channels (depolarization), followed by K+ efflux (repolarization) and brief hyperpolarization.

Question: Which part of the neuron is responsible for receiving signals?

  1. Axon terminals
  2. Axon
  3. Dendrites (correct answer)
  4. Myelin sheath
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies dendrites as playing a key role in receiving signals, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that the axon receives signals, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 4

Scenario—Signal Transmission: A neuron conducts an action potential from the axon hillock down the axon to axon terminals. In myelinated axons, myelin insulates the membrane and action potentials are regenerated at nodes of Ranvier, speeding transmission. At synapses, neurotransmitters released from the presynaptic terminal cross the synaptic cleft and bind receptors on the postsynaptic membrane.

Diagram (text-only): Soma—Hillock—[Myelin]o[Myelin]o[Myelin]—> Terminals ^ nodes of Ranvier (o)

Question: Describe how action potentials are propagated along a myelinated axon.

  1. They continuously depolarize every axon segment under myelin
  2. They jump node-to-node where voltage-gated channels cluster (correct answer)
  3. They travel backward from terminals to the soma
  4. They cross synapses directly without neurotransmitters
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies saltatory conduction jumping node-to-node as playing a key role in propagation along myelinated axons, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that action potentials travel backward, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 5

Scenario—Neuron Anatomy: Dendrites and soma receive and integrate graded potentials. If summed inputs reach threshold at the axon hillock, an action potential begins and travels along the axon to the axon terminals.

Diagram (text-only): [Dendrites] → (Soma: integration) → [Axon hillock: threshold] → Axon → Terminals

Question: How does the structure of an axon facilitate action potential transmission?

  1. It contains receptors that primarily receive synaptic input
  2. It conducts action potentials away from the soma toward terminals (correct answer)
  3. It houses the nucleus and most protein synthesis machinery
  4. It prevents any ion movement across the membrane
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies the axon conducting action potentials away from the soma as playing a key role in transmission, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that the axon receives synaptic input, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 6

Scenario—Signal Transmission: An action potential is initiated at the axon hillock and propagates down the axon because depolarization in one segment brings the next segment to threshold. After firing, refractory periods help ensure one-way propagation. Neurotransmitters carry the signal across the synaptic cleft.

Question: Which part of the neuron is responsible for receiving signals?

  1. Dendrites (correct answer)
  2. Axon hillock
  3. Axon
  4. Nodes of Ranvier
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies dendrites as playing a key role in receiving signals, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that the axon hillock receives signals, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 7

Scenario—Action Potential Process: During an action potential, after the peak, Na+ channels are inactivated and K+ channels remain open briefly, causing the membrane potential to become more negative than resting (hyperpolarization) before returning to baseline.

Question: Which ion movement is most critical for repolarization?

  1. Na+ efflux through voltage-gated Na+ channels
  2. K+ influx through voltage-gated K+ channels
  3. K+ efflux through voltage-gated K+ channels (correct answer)
  4. Cl− influx through voltage-gated Cl− channels
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies K+ efflux through voltage-gated K+ channels as playing a key role in repolarization, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that K+ influx is critical for repolarization, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 8

Scenario—Action Potential Process: Threshold depolarization opens voltage-gated Na+ channels, rapidly driving the membrane potential toward positive values. This is followed by Na+ channel inactivation and delayed opening of voltage-gated K+ channels.

Question: What occurs during the depolarization phase of an action potential?

  1. K+ exits the cell as voltage-gated K+ channels open
  2. Na+ enters the cell as voltage-gated Na+ channels open (correct answer)
  3. Na+/K+ pumps reverse direction and depolarize the membrane
  4. Neurotransmitters diffuse along the axon to the terminals
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies Na+ entering the cell as voltage-gated Na+ channels open as playing a key role in depolarization, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that K+ exits during depolarization, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 9

Scenario—Signal Transmission: In myelinated axons, myelin reduces ion leakage and concentrates voltage-gated channels at nodes of Ranvier. Depolarization spreads quickly under myelin, and action potentials are regenerated at nodes.

Question: Describe how action potentials are propagated along a myelinated axon.

  1. They regenerate at nodes, producing saltatory conduction (correct answer)
  2. They diffuse as neurotransmitters through the axoplasm
  3. They require dendrites to relay signals between nodes
  4. They stop at each myelin segment until pumps restore ions
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies regeneration at nodes producing saltatory conduction as playing a key role in myelinated axon propagation, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that they diffuse as neurotransmitters, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 10

Scenario—Neuron Anatomy: Dendrites receive synaptic input, the soma integrates signals, and the axon transmits action potentials to terminals. Membrane potential depends on ion gradients and permeability.

Question: Which part of the neuron is responsible for receiving signals?

  1. Soma
  2. Dendrites (correct answer)
  3. Axon
  4. Axon hillock
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies dendrites as playing a key role in receiving signals, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that the soma receives signals primarily, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 11

Scenario—Action Potential Process: Voltage-gated channels respond to changes in membrane potential. Na+ channel opening causes depolarization; K+ channel opening causes repolarization and contributes to hyperpolarization.

Question: What is the role of ion channels during an action potential?

  1. They allow selective Na+ and K+ movement to change membrane voltage (correct answer)
  2. They prevent ions from crossing the membrane during firing
  3. They carry neurotransmitters across the synaptic cleft
  4. They maintain resting potential by producing ATP
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies ion channels allowing selective Na+ and K+ movement as playing a key role in changing membrane voltage, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that they prevent ions from crossing, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 12

Scenario—Neuron Anatomy: The axon hillock is the trigger zone where graded potentials are summed and threshold is reached to initiate an action potential. Dendrites receive inputs; the soma integrates; the axon conducts.

Question: What occurs during the depolarization phase of an action potential?

  1. Voltage-gated Na+ channels open and Na+ enters the neuron (correct answer)
  2. Voltage-gated K+ channels open and K+ enters the neuron
  3. Na+ channels inactivate and prevent any voltage change
  4. Neurotransmitters are released from dendrites into the cleft
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies voltage-gated Na+ channels opening and Na+ entering as playing a key role in depolarization, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that K+ enters during depolarization, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 13

Scenario—Signal Transmission: Myelin increases conduction speed by enabling saltatory conduction. Nodes of Ranvier contain many voltage-gated Na+ and K+ channels, allowing action potentials to be regenerated at discrete points.

Question: Describe how action potentials are propagated along a myelinated axon.

  1. They jump between nodes where action potentials are regenerated (correct answer)
  2. They move only through the soma before reaching terminals
  3. They require continuous neurotransmitter release along the axon
  4. They travel from terminals back to the axon hillock
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies jumping between nodes where action potentials are regenerated as playing a key role in myelinated axon propagation, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that they travel from terminals back, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 14

Scenario—Neuron Anatomy: Dendrites are branched processes specialized for receiving synaptic signals; the soma contains the nucleus and integrates input; the axon is a long process specialized for transmitting action potentials.

Question: Which part of the neuron is responsible for receiving signals?

  1. Axon
  2. Dendrites (correct answer)
  3. Soma
  4. Axon terminals
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies dendrites as playing a key role in receiving signals, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that the axon receives signals, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 15

Scenario—Signal Transmission: Action potentials propagate along an unmyelinated axon as a wave of depolarization, with each adjacent segment reaching threshold. This relies on local current flow and the distribution of voltage-gated channels.

Question: How does the structure of an axon facilitate action potential transmission?

  1. It provides a continuous membrane for sequential depolarization (correct answer)
  2. It contains dendritic spines for receiving synapses
  3. It stores neurotransmitters in the nucleus
  4. It prevents refractory periods from occurring
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies the axon providing a continuous membrane for sequential depolarization as playing a key role in transmission, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that it contains dendritic spines, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 16

Scenario—Action Potential Process: Depolarization is driven by Na+ influx. Repolarization occurs as Na+ channels inactivate and K+ channels open, allowing K+ to leave the cell, returning the membrane potential toward resting.

Question: What occurs during the depolarization phase of an action potential?

  1. Na+ enters through voltage-gated Na+ channels (correct answer)
  2. K+ enters through voltage-gated K+ channels
  3. K+ exits through ligand-gated K+ channels
  4. Cl− enters through voltage-gated Cl− channels
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies Na+ entering through voltage-gated Na+ channels as playing a key role in depolarization, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that K+ enters during depolarization, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 17

Scenario—Action Potential Process: Repolarization follows the peak of the action potential when voltage-gated K+ channels open and K+ leaves the cell, moving the membrane potential back toward negative values.

Question: Which ion movement is most critical for repolarization?

  1. Na+ influx
  2. K+ efflux (correct answer)
  3. Ca2+ influx
  4. Cl− efflux
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies K+ efflux as playing a key role in repolarization, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that Na+ influx is critical for repolarization, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 18

Scenario—Signal Transmission: In saltatory conduction, myelin insulates internodes, and action potentials are regenerated at nodes of Ranvier where voltage-gated channels are concentrated. This increases conduction velocity along the axon.

Question: Describe how action potentials are propagated along a myelinated axon.

  1. They regenerate at nodes, effectively skipping myelinated internodes (correct answer)
  2. They are carried by neurotransmitters down the axon membrane
  3. They require the soma to depolarize repeatedly for each node
  4. They move from dendrites to dendrites without using the axon
Explanation: This question tests foundational knowledge of neuron structure and action potentials in Anatomy & Physiology. Neuron anatomy involves structures such as dendrites, axons, and soma, each playing a crucial role in signal transmission. Action potentials are electrical signals generated by the movement of ions across the neuron's membrane, primarily through ion channels. In this passage, the focus is on how ion channels regulate action potentials by facilitating the flow of ions such as Na+ and K+, which are critical for depolarization and repolarization phases. The correct answer identifies regeneration at nodes effectively skipping internodes as playing a key role in myelinated axon propagation, demonstrating an understanding of how neuron structures facilitate signal transmission. A common distractor might suggest that they are carried by neurotransmitters, which reflects a misunderstanding of neuron anatomy and function. Teaching strategies include using diagrams to reinforce the spatial orientation of neuron parts and conducting exercises that trace the action potential pathway to reinforce the sequence and role of ion channels.

Question 19

During an action potential, voltage-gated sodium channels undergo inactivation. A student observes that a neuron cannot generate a second action potential immediately after the first one, even when stimulated with a very strong depolarizing current. This refractory period is primarily due to:

  1. Depletion of intracellular sodium ions that need time to be replenished by the sodium-potassium pump
  2. Voltage-gated sodium channels being in their inactivated state and unable to reopen until the membrane repolarizes (correct answer)
  3. Excessive potassium efflux that hyperpolarizes the membrane below the threshold for sodium channel activation
  4. Temporary exhaustion of cellular ATP needed to power the voltage-gated sodium channels during depolarization
  5. Calcium influx through sodium channels that blocks further sodium entry until calcium is actively transported out
Explanation: Understanding the refractory period requires grasping how voltage-gated sodium channels operate during action potentials. These channels have three distinct states: closed (resting), open (activated), and inactivated - and this third state is crucial to neuronal function. During an action potential, sodium channels first open when the membrane depolarizes to threshold, allowing sodium influx. However, within milliseconds, these same channels automatically inactivate - they close and become temporarily unable to reopen, even if the membrane remains depolarized. This inactivation persists until the membrane repolarizes back toward resting potential, at which point the channels reset to their closed but available state. Option B correctly identifies this mechanism. The absolute refractory period occurs because sodium channels are stuck in their inactivated state, making it impossible to generate another action potential regardless of stimulus strength. Option A is wrong because sodium depletion doesn't occur - only tiny amounts of sodium enter during each action potential, and the sodium-potassium pump works continuously, not just between action potentials. Option C misunderstands the relative refractory period; while potassium efflux does contribute to hyperpolarization later, the absolute refractory period is entirely due to sodium channel inactivation, not potassium effects. Option D incorrectly suggests voltage-gated channels require ATP - they're powered by the electrochemical gradient, not direct ATP hydrolysis. Remember: voltage-gated sodium channels have three states, not just open/closed. The inactivated state is what prevents immediate repeated firing and ensures action potentials propagate in one direction.

Question 20

A researcher applies tetrodotoxin (TTX), which blocks voltage-gated sodium channels, to a neuron and then stimulates it. She observes that small depolarizations can still occur in response to stimulation, but no action potentials are generated. The small depolarizations are most likely due to:

  1. Sodium ions entering through ligand-gated channels that are not affected by TTX (correct answer)
  2. Potassium ions leaving the cell more slowly because sodium entry is blocked
  3. Calcium ions entering through voltage-gated calcium channels that open at subthreshold potentials
  4. Residual sodium entry through partially blocked voltage-gated sodium channels
  5. Chloride ions leaving the cell through voltage-gated chloride channels activated by the stimulus
Explanation: When you encounter questions about neurotransmission and channel blockers, focus on understanding which specific channels are affected and what alternative pathways remain available for ion movement. TTX specifically blocks voltage-gated sodium channels, which are essential for action potential generation. However, neurons have multiple types of ion channels that can allow depolarization through different mechanisms. Since the researcher observes small depolarizations despite TTX treatment, ions must still be entering the cell through TTX-unaffected channels. Answer A is correct because ligand-gated sodium channels operate through a completely different mechanism than voltage-gated channels. These channels open when neurotransmitters bind to them, not in response to voltage changes. Since TTX only blocks voltage-gated sodium channels, ligand-gated channels remain functional and can still allow sodium influx, creating small depolarizations. Answer B is incorrect because slower potassium efflux would actually help maintain depolarization longer, not create new depolarization. The small depolarizations observed require ion influx, not reduced efflux. Answer C is wrong because while calcium entry can contribute to depolarization, voltage-gated calcium channels typically require higher threshold potentials than those needed for the "small depolarizations" described in this subthreshold scenario. Answer D is incorrect because TTX completely blocks voltage-gated sodium channels when applied effectively. The question states that no action potentials occur, confirming complete blockade of these channels. Remember: Channel blockers are usually specific to one type of channel. When one pathway is blocked, always consider what alternative ion movement pathways remain available to explain continued electrical activity.