Resting membrane potential and Action potentials

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 • http://www.youtube.com/watch?v=U0NpTdge3aw • http://www.youtube.com/watch?v=7EyhsOewnH4&feature=related

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