Which of the following actions allows for repolarization of a neuron?
A.
The inhibition of sodium and potassium pumps, stopping all ion movement into the neuron
B.
The opening of sodium channels, allowing sodium to enter the neuron
C.
The closing of both sodium and potassium channels to restrict movement of ions into and out of the
D.
neuron
The Correct Answer and Explanation is:
Correct Answer: C. The closing of both sodium and potassium channels to restrict movement of ions into and out of the neuron
Explanation:
Repolarization is a critical phase in the action potential of a neuron, which is essential for returning the membrane potential to its resting state after depolarization. To understand how repolarization occurs, it’s important to first grasp the phases of an action potential and the roles of different ion channels in this process.
- Action Potential Phases: The action potential has several phases: depolarization, repolarization, and hyperpolarization. During depolarization, sodium channels open, allowing Na+ ions to rush into the neuron. This influx of positively charged sodium ions causes the membrane potential to become more positive. Following depolarization, repolarization occurs, where the membrane potential returns to its resting state.
- Role of Ion Channels:
- Sodium Channels: These channels open during depolarization, allowing Na+ to enter the neuron. As the action potential peaks, sodium channels begin to close, which is crucial for ending the influx of sodium.
- Potassium Channels: During the peak of the action potential, voltage-gated potassium channels open, allowing K+ to exit the neuron. This outflow of potassium helps to bring the membrane potential back towards its resting level.
- Repolarization Mechanism: To return to the resting membrane potential, the neuron needs to restore the balance of ions across the membrane. During repolarization:
- Sodium channels close to stop the inward flow of Na+.
- Potassium channels remain open to allow K+ to leave the neuron, further aiding in bringing the membrane potential back to a negative value.
- Inhibition of Ion Movement: The option C correctly describes that closing both sodium and potassium channels (or limiting their activity) restricts the movement of ions into and out of the neuron. This cessation of ion movement helps in stabilizing the membrane potential as the neuron returns to its resting state.
- Misconceptions in Other Options:
- Option A: Inhibiting sodium and potassium pumps would disrupt ion gradients, leading to failure in repolarization and maintaining the resting membrane potential.
- Option B: The opening of sodium channels increases depolarization rather than repolarization.
- Option D: While closing sodium and potassium channels may aid in stabilization, it’s not the complete process for repolarization, which requires specific timing and coordination of channel activities.
In summary, the closing of sodium and potassium channels restricts ion movement, contributing to the stabilization of the membrane potential and the repolarization of the neuron.