1. Resting membrane potential and Action potentials
Sending a signal

2. Review Ions are charged particles
Examples of ions Na+, K+ (the + means they have a possitive charge)
There are lots of ions in our bodies
Ions are used to control the polarity or charge inside and outside of our cells

3. Review cont.
Plasma membranes separates the inside of a cell (in this case a neuron) from the outside
It contain proteins that act as channels (gateways) for certain ions
The channels are small
The channels only allow specific ions to pass through them

4. Resting membrane potential
All cells have a negatively charged inside compared to their outside.
How do cells maintain their resting membrane potential?
Lots of Na+ ions outside of cell
Outside the cell
Inside the cell
Lots of K+ ions inside of cell

5. Sodium-Potassium pump
At rest Sodium-potassium pumps function to maintain the negative internal environment of the cell
How?
Sodium potassium pump pumps out three Na+ ions for every two K+ ions it takes in
Net negative charge inside as compared to the outside of the cell

6. Sodium-Potassium pump cont.
Na+ K+
The sodium potassium pump keeps high a high concentration of Na+ outside of the cell and a low concentration inside
It also keeps a high concentration of K+ inside the cell and a low concentration inside.
Outside the cell
Lots of Na+ ions outside of cell
Inside the cell

7. Action potential
An action potential is a temporary reversal of the polarity (charge) inside the cell compared to the outside
This action potentials are responsible for sending signals in a neuron
Steps to an action potential
Depolarization
Repolarization
Return to resting membrane potential

8. Depolarization
This is the rapid change of a negative charge inside the cell to a positive charge
How it works
Voltage gated sodium channels open
High concentration of sodium outside rushes to area of low concentration inside the cell
Influx of positive ions into the cell
Cells interior becomes positive compared to outside

9. + + + - - - + + + + + + + + - - - - - - - - + + + + + + + +
Depolarization
Sodium Channel
Potassium Channel
K+ ions
Na+ ions

10. Repolarization
Repolarization is the return to a negative interior of the cell
This occurs very quickly after the Na+ enters the cell
How it works
Voltage gated K+ channels open
High concentration of K+ inside the cell compared to the outside
K+ rushes out of the cell
Loss of large amounts of positive charge return the interior of the cell to negative state

11. Depolarization then repolarization
Sodium Channel
Potassium Channel
K+ ions
Na+ ions

12. Return to resting state
Repolarization makes the internal environment of the cell too negative (called an overshoot)
There is also a lot of sodium on the inside of the cell and lots of potassium on the outside (opposite of desired)
Sodium-potassium pumps kick in to return the concentrations to pre-action potential levels

13. All or nothing AP Action potentials are all or nothing signals
You can not have a small action potential in a neuron, it either happens or it does not
If the stimulus is not large enough an action potential will not occur
Action potentials only occur when a cell reaches threshold
Once threshold is reached an action potential will occur