Note: Question is incomplete i have added full question and answer in the attachment.
Answer:
These three steps occur once the membrane potential reaches threshold.
- many voltage-gated Na+ channels open
- Na+ ions rush into the cell
- membrane potential rises
Step-by-step explanation:
When membrane achieve threshold sodium-potassium gates opens and let the sodium pass into the cell from outside of membrane. This mechanism is called membrane depolarization. As this mechanism occur membrane voltage achieve resting membrane potential. See image for better understanding how it happens.