Final answer:
The speed of the late repolarization phase of the fast action potential can be attributed to the opening of K+ channels, which leads to the outward flow of K+ ions, and the closure of Ca²+ channels, which terminates the plateau phase and initiates repolarization.
Step-by-step explanation:
The speed of the late repolarization phase of the fast action potential can be explained by two factors:
1. Opening of K+ channels:
During repolarization, K+ channels open and K+ ions flow out of the cell. This outward flow of potassium ions helps restore the membrane potential to its resting level. The rapid movement of K+ ions out of the cell accelerates the repolarization phase, leading to a faster rate of repolarization.
2. Closure of Ca²+ channels:
At the end of the plateau phase, Ca²+ channels close, preventing the further influx of calcium ions into the cell. This closure of Ca²+ channels plays a crucial role in terminating the plateau phase and initiating repolarization. By closing the Ca²+ channels, the cell is able to shift from the plateau phase to the repolarization phase more quickly, contributing to the faster speed of repolarization.