Final answer:
An action potential is an electrical impulse that transmits down a neuron when it is stimulated, involving a rapid change in electrical charge across the neuron's membrane due to the flux of Na+ and K+ ions.Hence, the correct answer is option B.
Step-by-step explanation:
An action potential in a neuron is defined as an electrical impulse that is transported down a neuron in response to a stimulus. This electrical charge travels along the membrane of a neuron, and it can be triggered when the neuron's membrane potential is altered by chemical signals from a nearby cell. In physiological terms, an action potential is a swift change from a negative to a positive charge inside the cell as sodium ions (Na+) flow in through ion channels, subsequently followed by potassium ions (K+) flowing out, which helps in restoring the initial electrical gradient.
During an action potential, initial depolarization occurs when the cell membrane becomes permeable to Na+ due to a stimulus. This leads to the inside of the neuron becoming positively charged in relation to the outside. Then, repolarization follows as the cell membrane becomes impermeable to Na+ and enables K+ ions to move out. Action potentials propagate along the neuron's axon as each segment of the membrane depolarizes and repolarizes, effectively transmitting an electrical signal quickly down the axon to communicate with other cells, potentially leading to muscular contractions or the activation of another neuron.
Meanwhile, active transport works to maintain the concentration differences of ions across the neuron's membrane, ensuring that even after firing multiple action potentials, the cell can continue to function properly without depleting its ionic gradients significantly.