Final answer:
An action potential is a neural event where the neuron 'fires' due to the movement of Na+ and K+ ions across its membrane, which happens in specific sequential phases, starting from depolarization to repolarization and resulting in the restoration of the resting potential.
Step-by-step explanation:
An action potential is a critical aspect of neural communication and involves a series of ionic movements across a neuron's membrane. When a neuron's membrane depolarizes to its threshold potential (usually around -55 mV), voltage-gated sodium channels open, leading to an influx of Na+ ions which raises the internal charge of the cell, causing depolarization up to approximately +40 mV. This all-or-nothing event, the action potential, triggers the neuron to "fire." Following this, a different set of channels, voltage-gated potassium channels, open allowing K+ ions to exit the neuron, leading to repolarization and eventually hyperpolarization of the neuron's membrane. The cell then returns to its resting state with the help of the Na+/K+ pump, which restores the resting potential.
Specifically, an action potential can be broken down into five distinct phases: (1) A stimulus causes initial depolarization; (2) Upon reaching the threshold, an action potential is triggered with a rapid depolarization due to Na+ influx; (3) K+ channels open while Na+ channels inactivate as the membrane potential peaks; (4) K+ efflux leads to repolarization and hyperpolarization, and (5) Na+/K+ pumps and other mechanisms restore the resting potential. During the refractory period, the neuron cannot fire another action potential, ensuring the impulse travels in one direction.