How is an action potential propagated along an axon?

• A. By the continuous opening of voltage-gated sodium channels along the axon
• B. By the release of neurotransmitters at each segment of the axon
• C. By the passive diffusion of ions through the axonal membrane
• D. By the active transport of potassium ions into the axon

Answer: (A)

Verified step by step guidance

1. Understand the concept of an action potential: An action potential is a rapid rise and subsequent fall in voltage or membrane potential across a cellular membrane with a characteristic pattern.
2. Identify the role of voltage-gated sodium channels: These channels open in response to a change in membrane potential, allowing sodium ions (Na+) to enter the neuron, which depolarizes the membrane and initiates the action potential.
3. Explain the propagation mechanism: Once an action potential is initiated at the axon hillock, it travels along the axon by the sequential opening of voltage-gated sodium channels. This creates a wave of depolarization that moves down the axon.
4. Clarify the role of myelination: In myelinated axons, the action potential jumps between nodes of Ranvier (gaps in the myelin sheath) in a process called saltatory conduction, which speeds up the propagation.
5. Differentiate from other options: The release of neurotransmitters occurs at synapses, not along the axon. Passive diffusion of ions and active transport of potassium ions are involved in maintaining resting potential and repolarization, not in the propagation of the action potential.