1/27/15 – Lecture 5 – Changing Membrane Potential- Goal: to understand how neurons produce transient electrical signals through the movement of ions through voltage-gated ion channels- Voltage Gated Ion Channels: channels opened by changes in voltage/ charge inside the cello Allows ions to move down their concentration gradients (high to low concentration) so no extra energy is required Na+ Voltage Gated Ion Channel (opens before its counter part – K+)- 3 States of the Na+ Gated Ion Channel1. Closed: channel is clused but alittle Na+ can leak through When the cell is atresting potential2. Open/ Activated: channel andinactivating segment are bothopen and lots of Na+ moves into the cell When there is a voltage change across the cell membrane3. Inactivated: channel is open or closed but the inactivating segment has swung shut so no Na+ can go through During the refractory period- Pattern of the Na+ Voltage Gated Ion Channel1. Closed -> Open (when inside of the cell is more positive2. Open -> Inactivated (when the short activated state is completed)3. Inactivated -> Closed (de-inactivates itself to then repeat the process) K+ Voltage Gated Ion Channel (opens slower than the Na+ Ion Channel because it requires more of a change to open)- 2 States of the K+ Gated Ion Channel1. Closed: channel is closed at resting potential2. Open/ Activated: channel is open when the voltage changes inside thecell to become more positive than at resting potential- Changes in Membrane Potentialo Sudden increase or decrease in membrane potential caused by movement of ions across the cell membrane Depolarization: when positive ions flow into the cell (or negativeions flow out of the cell) and it becomes less negative insidecompared to the outside the cell Hyperpolarization: when positive ions flow out of the cell (ornegative ions flow into the cell) and it becomes more negativeinside the cell compared to the outside of the cell- Pumps always catch back up and return to the restingmembrane potential- Polarization: when a cell is either positive or negative1. Depolarizing: closer to 0 mV with less polarization2. Hyperpolarizing: farther from 0 mV When an extremely large amount of positive ions are pulsed in and passes a critical threshold …. Causes an ACTION POTENTIALo Action Potential: rapid, transient, all-or-nothing change in membrane potential Depolarization: inside of the cellbecomes less negative Repolarization: inside of cellbecomes/ returns to negativepolarization Hyperpolarization: over shootsthe negative polarization of themembrane’s resting potential(becomes more negative)- Pumps catch up andreturn the cell to resting potential Voltage Gated Na+ channel: opened by small changes in depolarization (opens 1st) Voltage Gated K+ channel: opened by larger changes in depolarization- Open and close much slower than the Na+ ion channels1. At rest, the Na+/K+ pump and the resting K+ channel produce a net negative charge inside of the cell compared to the outside2. Depolarization opens voltage gated Na+ channels Na+ travels inside quickly and makes the inside of the cell more positive3. After a delay, voltage gated K+ channels open, at the same time the voltage gated Na+ channels close and inactivate Membrane repolarizes by K+ ions going back out of the cell4. Inactivation of the Na+ channels and opening in voltage gated K+ channels result in “overshoot” of resting membrane potential, causing hyper polarization5. Closed Na+ channels de-inactivate, voltage gated K+ channel closes, Na+/ K+ pumps return Na+ and K+ gradients to normal, membrane potential returns to normalo Chamelopathies: diseases caused by mutations affecting the ion specificity, voltage sensitivity, opening, closing, or inactivation of voltage gated ion channels More likely to fire if the Na+ channels opened to quickly- Epilepsy: disorder characterized by seizures with too many signals being fired in the brain… caused by genetics or environmental factors… triggered by flashing lights, infections, brain tumors/ traumas Fewer or no signals if the Na+ channels didn’t open- Being unable to feel pain when Na+ gated neurons won’t open in their pain sensing