An action potential is a rapid change in the electrical charge across a neuron's membrane, allowing it to transmit signals. This process begins when a neuron receives a stimulus, causing sodium ions to flow into the cell. When the internal charge reaches a certain threshold, an action potential is triggered, resulting in a wave of electrical activity that travels along the neuron. During the action potential, potassium ions exit the neuron, restoring the original charge. This sequence of events is crucial for communication between neurons and is fundamental to the functioning of the nervous system, including processes like muscle contraction and reflexes.