1. Action Potential Analogy

2. The way neurons send messages to each other is like 2 people going on the tops of buildings using mirrors to reflect the sun and send messages to each other.
Charlotte
Daniel

3. First, they must climb to the top of the building.
Charlotte and Daniel cannot simply teleport to the top of the building to send the messages.
First, they must climb to the top of the building.
Climbing to the top of the building is analogous to the chain reaction (action potential) down an axon.

4. Hanging out in the lobby of the building is analogous to resting potential

5. Some things can move in and out of the lobby easily, some cannot, much like the cell membrane
 Notice that some molecules are too large to pass the barrier. Some must enter through transport protein

6. Charlotte and Daniel must climb one flight of stairs at a time
Charlotte and Daniel must climb one flight of stairs at a time. They cannot just teleport to the roof (and there’s no elevator). This is analogous to the cascade of sodium channels opening.
One sodium channel opens up, allowing sodium to rush into the axon. This causes the inside to become more positive (more positive ions moving in). This sets off a chain reaction, so more and more channels open further down, making the inside of the neuron more and more positive.
Depolarization

7. Depolarization is when the interior of the cell is becoming more positive (Remember at resting potential, it is negative)
Depolarization is like starting from the 3rd floor and heading to the roof. There is a smaller difference between the charge of the inside and outside of the cell (much like having less of a distance to climb to the roof).
The cell does not need to become as positive to pass on to the next neuron.
Easier for action potential to occur

8. Repolarization is when the interior of the cell is returning to resting potential
During repolarization, sodium channels close and potassium channels open, allowing them to exit the cell (positive ions moving out, so the exterior becomes more positive relative to the interior)

9. Hyperpolarization is when the interior of the cell is becoming more negative
Hyperpolarization is like starting from the basement and heading to the roof. There is a larger difference between the charge of the inside and outside of the cell (much like having more of a distance to climb to the roof).
The cell does not need to become more positive to pass on to the next neuron.
Harder for action potential to occur

10. Quantified Summary
-75 mV : polarization  -75 mV going to +50 mV : DEpolarization  +50 mV going to -75 mV : REpolarization  -75 mV going to -90 mV : HYPERpolarization