Which of the following increases the speed of action potential propagation down the axon?

• A. Higher concentration of sodium ions outside the neuron
• B. Increased number of synapses
• C. Myelination of the axon
• D. Increased axon diameter

Answer: (C)

Verified step by step guidance

1. Understand the concept of action potential propagation: Action potentials are electrical signals that travel along the axon of a neuron. The speed of this propagation can be influenced by several factors.
2. Consider the role of myelination: Myelin is a fatty substance that wraps around the axon, forming an insulating layer. This insulation allows the action potential to jump between gaps in the myelin sheath, known as nodes of Ranvier, in a process called saltatory conduction.
3. Evaluate the effect of myelination: Myelination significantly increases the speed of action potential propagation because it reduces the amount of axon membrane that needs to be depolarized, allowing the signal to travel faster.
4. Compare with other factors: While a higher concentration of sodium ions outside the neuron is necessary for action potential generation, it does not directly increase propagation speed. Similarly, an increased number of synapses can actually slow down signal transmission due to synaptic delay.
5. Consider axon diameter: An increased axon diameter can also increase the speed of action potential propagation by reducing the internal resistance to the flow of ions. However, myelination has a more pronounced effect on increasing speed.