Final answer:
An action potential in a neuron is characterized by the rapid influx of Na+ ions followed by the outflow of K+ ions. This results in the depolarization and subsequent repolarization of the neuron's membrane, and is restored to resting potential by the action of the sodium-potassium pump.
Step-by-step explanation:
The best description of an action potential in a neuron is that it involves the rapid inflow of Na+ ions into the neuron, followed by the outflow of K+ ions. This process includes the following steps:
- Depolarization: When a stimulus reaches a neuron, voltage-gated Na+ channels open, allowing Na+ ions to rush into the cell. This causes the inside of the neuron to become more positive and leads to depolarization.
- Repolarization: After a short delay, voltage-gated K+ channels open, allowing K+ ions to leave the cell, which repolarizes the membrane, bringing the charge back towards the resting potential.
- Hyperpolarization and Restoration: Often, the efflux of K+ ions can overshoot the resting potential, leading to slight hyperpolarization. The sodium-potassium pump then restores the resting potential by actively moving Na+ ions out of the neuron and K+ ions back in, using ATP as an energy source.
This cycle of depolarization and repolarization constitutes an action potential, which travels down the axon to transmit a neural signal. The given options, the correct choice is (B): Na+ ions rush into the cell, followed by the release of K+ ions.
An action potential is an all-or-nothing event signifying that once the threshold is reached, it will proceed fully. During this process, Na+ channels are inactivated, so no more Na+ ions enter the cell. This sequence leads to the neuron being able to fire continuously without substantial depletion of ion concentrations and is crucial for neuronal communication.