Depolarization is initiated when there is an influx of sodium inside the cell as opposed to repolarization, where potassium exits the cell (occurring after Na+ gates close). Remember that for every 3 Na+ in, there is 2 K+ out. This imbalance helps to stabilize the membrane.
Explanation: Survivorship curves fit three types. A Type I curve shows a low death rate in early and middle life but the death rate increases steeply in old age. A Type II curve shows a death rate is more constant throughout the lifetime of the species.
Every action has an equal and opposite reaction. I would assume that the energy in the other direction would be an action.. though I'm not entirely sure. I hope it helps.
