1st Edition NSCI 110 Lecture 9 Outline of Last Lecture I Hyperpolarization and depolarization both involve changes in membrane potential II An electrochemical gradient in a neuron is formed by contributions from ion diffusion and electrical gradients III There are four key ions involved in giving a neurons its resting membrane potential IV Ion channels consist of membrane spanning proteins a Cause the membrane to be porous and selective V There are passive and active factors that contribute to generating an action potential down an axon VI Each ion has a different permeability to the membrane VII Equilibrium potential is the voltage at which the flow of a specific ion through a membrane is equal or balanced in both directions Outline of Current Lecture II Action potentials have three fundamental properties III Voltage activated ion channels can have activation and inactivation gates a Neurons have voltage activated sodium and potassium channels IV There are multiple phases of an action potential a Absolute refractory period i Rising phase depolarization ii Falling phase repolarization b Relative refractory period i Deactivation states ii Hyperpolarization Current Lecture I II An action potential has three unique properties a Carries a threshold b Conducts all or none c Exhibits self propagation Voltage activated sodium channel includes an activation extracellular side and inactivation gate cytosolic side a Activation gate normally shut at resting membrane potential inactivation gate normally open i Activation gate opens when cell depolarizes and sodium flows into the cell rapidly These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute III IV V b Inactivation gate then shuts and halts the influx of sodium when the peak of depolarization is reached c When membrane is repolarizing a transitional phase occurs i Inactivation gate reopens and activation gate closes back into starting position 1 Called the deactivated state Voltage activated potassium channel includes just an activation gate a Has a higher activation threshold that takes longer to open the activation gate and let potassium ions out of the cell i Does not occur until after some sodium influx occurs b Both gates reset activation gates when a cell is hyperpolarized Examining current in a number of ion channels a TEA blocks K channels and TTX blocks Na channels i Using TEA results in a short Na influx ii Using TTX results in a longer K efflux because these gates take longer to reach activation potential Phases of the action potential a During the rising phase of the absolute refractory period the membrane is depolarized i The membrane is repolarized during the falling phase of the absolute refractory period ii At this point after reaching the threshold it exhibits the all or none principle b During the relative refractory period the membrane hyperpolarizes i Cannot generate another action potential until the activation gates in the sodium channels are reset in their deactivation states ii Usually need a stronger stimulus larger voltage to reach threshold because of an overshoot extra negative charge during hyperpolarization c Action potentials can be generated again as soon as gates are reset even above the threshold
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