Final answer:
An action potential (AP) will not run out of energy as it travels down an axon; it is regenerated at full strength at each point along the path in unmyelinated axons and at the nodes of Ranvier in myelinated axons. The process is all-or-none, ensuring that the signal maintains its strength to the end.
Step-by-step explanation:
If an AP starts at one end of an axon, it will not run out of energy because the action potential (AP) is an all-or-none event. When an AP is generated, it triggers a wave of depolarization that travels down the axon to its end. This process occurs without a loss of strength because at each point along the axon, the electrical impulse is regenerated at full strength, much like a relay. In the case of unmyelinated axons, as the positively charged sodium ions (Na+) enter through voltage-gated Na+ channels, they move along the inside of the membrane, causing more of the membrane to depolarize and thereby activating more Na+ channels ahead of the impulse, propagating the AP. However, in myelinated axons, propagation occurs faster and with less energy input in the myelinated regions, but with periodic regeneration at the nodes of Ranvier. Here, the distance between nodes is strategically positioned so that the depolarization remains above the threshold for activating voltage-gated Na+ channels at the next node, allowing the signal to move efficiently and be regenerated as it travels down the axon. Therefore, although the signal loses voltage in myelinated regions, it does not run out of energy. It is systematically regenerated in the gaps (nodes of Ranvier), allowing the signal to maintain its strength all the way down the axon until it reaches the terminal buttons.