Resting membrane potential and Action potentials Sending a signal

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

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

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

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

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

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

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

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

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

Depolarization then repolarization Sodium Channel Potassium Channel + + + - - - + + + + + + + + - - - - - - - - + + + + + + + + - - - - - - - - K+ ions Na+ ions

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

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