The Question is from neet-zoology neural-control-and-coordination generation-and-conduction-of-nerve-impulse, and it was created by the author BALASOURY

Question

A specific neurotoxin selectively blocks voltage-gated potassium channels in a neuron. What is the most likely effect on the action potential?

BALASOURY · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
 **Primary Concept**: Action potential generation and repolarization
 **Related Topics**: Voltage-gated ion channels, membrane potential, neurotoxins
 **Prerequisites**: Understanding of the role of potassium channels in neuronal function, the phases of an action potential.
## SOLUTION PATHWAY
**Given Information**:
  A neurotoxin blocks voltage-gated potassium channels.
  [Important conditions]  The toxin selectively targets potassium channels, meaning other channels (sodium, calcium) remain functional.
**Method & Steps**:
 1. Understand the role of potassium channels in action potentials.
  Reasoning: Voltage-gated potassium channels open during the repolarization phase of the action potential, allowing potassium ions ($K^+$) to flow out of the neuron. This outward flow of positive charge restores the negative membrane potential.
  Formula/Rule:  No specific formula is needed here, but the understanding of the movement of ions across the membrane is crucial.
 2. Analyze the effect of blocking potassium channels.
  Working: If the potassium channels are blocked, the outflow of $K^+$ ions is prevented or significantly reduced. This means the neuron will take longer to repolarize.
  Key Point: The membrane potential remains more positive for a longer duration.
 3. Determine the consequence on the action potential.
  Result: The action potential will be prolonged because repolarization is delayed.  The neuron will remain depolarized for a longer period.
  Verification: The other options are incorrect because blocking potassium channels doesn't directly affect depolarization rate (A), prevent action potential initiation (C), or cause hyperpolarization (D).
 ## OPTION ANALYSIS
A :x: Increased rate of depolarization: Depolarization is primarily driven by sodium channels, which are unaffected by the toxin.
B ✓: Delayed repolarization and prolonged action potential: This is the correct answer because blocking potassium channels prevents the rapid repolarization phase of the action potential.
C :x: Prevention of action potential initiation: Action potential initiation depends on sodium channels, which are unaffected.
D :x: Hyperpolarization beyond the resting membrane potential:  Blocking potassium channels would prevent hyperpolarization, not cause it. Hyperpolarization requires an increase in potassium permeability.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the roles of sodium and potassium channels: Remember sodium channels are responsible for depolarization, and potassium channels for repolarization.
  2.Assuming the toxin affects all ion channels: The problem states the toxin is specific to potassium channels.
 **Quick Tips**:
  1. Visualize the action potential graph and consider how each ion channel contributes to its shape.
  2. Remember that repolarization is primarily driven by potassium efflux.

BALASOURY · Answer

Increased rate of depolarization

BALASOURY · Answer

The correct Option is "Delayed repolarization and prolonged action potential"

BALASOURY · Answer

Prevention of action potential initiation

BALASOURY · Answer

Hyperpolarization beyond the resting membrane potential

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