Embryonic stem cells,
Tissue-specific stem cells.
The way that you could use molecular biology to determine whether these birds have evolved from a shared common ancestor is to take a look at their proteins, RNA, and DNA. Because the more similar these things are in the two types of birds, the more possible it is that they are somewhat connected via a common ancestor.
Action potential is a mechanism of transfer of ions across the plasma membrane down their elctrochemical gradient. Action potential is regenerated by the influx of ions such as sodium in case of voltage gated sodium channels. The voltage gated channels can be either open or closed depending on the action potential. Depolarization of membrane leads to the opening of these channels that allow the sodium ions to enter the cell down their electrochemical gradient. The threshold of action potential is reached when the entry of sodium ions out reach the exit of potassium ions from the cell. This leads to the generation of action potential.
