Multiple Choice
Which of the following is most directly responsible for the falling (repolarizing) phase of the action potential in a neuron?
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45. Nervous System
Neurons and Action Potentials
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A certain toxin blocks voltage-gated potassium (K^+) channels in neurons. What is the likely impact of this toxin on the resting potential of a neuron?
A
The resting potential remains unchanged.
B
The resting potential becomes more negative (hyperpolarizes).
C
The neuron cannot generate any action potentials.
D
The resting potential becomes less negative (depolarizes).
Verified step by step guidance1
Step 1: Understand the role of voltage-gated potassium (K⁺) channels in neurons. These channels are crucial for repolarizing the membrane after an action potential and maintaining the resting potential by allowing K⁺ ions to flow out of the cell.
Step 2: Recall that the resting potential of a neuron is typically maintained at a negative value (around -70 mV) due to the selective permeability of the membrane to K⁺ ions, which exit the cell down their concentration gradient.
Step 3: Consider the effect of blocking voltage-gated K⁺ channels. If these channels are blocked, K⁺ ions cannot exit the cell efficiently, disrupting the balance of ion movement that maintains the resting potential.
Step 4: Analyze the impact of reduced K⁺ efflux. With fewer K⁺ ions leaving the cell, the inside of the neuron becomes less negative compared to the outside, leading to depolarization (a less negative resting potential).
Step 5: Conclude that the toxin's effect on blocking K⁺ channels results in the resting potential becoming less negative (depolarizes), as the normal ionic gradient is altered.
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