The three stages of Action Potential are:
1. depolarization- Na+ channels open up inside of the membrane and becomes more positive than the RMP.
2. repolarization- The Na+ channels inactivating and K+ channels opening AP spike stops rising to which the membrane returns to RMP.
3. hyperpolarization- A few of the K+ channels remain open and the Na+ channels reset inside of membrane becomes more negative than RMP.
Hope this helps!
xo