NSCI 110 1st Edition Lecture 9 Outline of Last Lecture I. Hyperpolarization and depolarization both involve changes in membrane potentialII. An electrochemical gradient in a neuron is formed by contributions from ion diffusion and electrical gradientsIII. There are four key ions involved in giving a neurons its resting membrane potentialIV. Ion channels consist of membrane-spanning proteinsa. Cause the membrane to be porous and selectiveV. There are passive and active factors that contribute to generating an action potential down an axonVI. Each ion has a different permeability to the membraneVII. Equilibrium potential is the voltage at which the flow of a specific ion through a membrane is equal or balanced in both directionsOutline of Current Lecture II. Action potentials have three fundamental propertiesIII. Voltage-activated ion channels can have activation and inactivation gatesa. Neurons have voltage-activated sodium and potassium channelsIV. There are multiple phases of an action potentiala. Absolute refractory periodi. Rising phase (depolarization)ii. Falling phase (repolarization)b. Relative refractory period i. Deactivation statesii. Hyperpolarization Current LectureI. An action potential has three unique propertiesa. Carries a thresholdb. Conducts “all or none”c. Exhibits self-propagationII. 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 openi. Activation gate opens when cell depolarizes and sodium flows into the cell rapidlyThese 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.b. Inactivation gate then shuts and halts the influx of sodium when the peak of depolarization is reachedc. When membrane is repolarizing, a transitional phase occursi. Inactivation gate reopens and activation gate closes (back into starting position)1. Called the deactivated stateIII. 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 celli. Does not occur until after some sodium influx occursb. Both gates reset activation gates when a cell is hyperpolarizedIV. Examining current in a number of ion channelsa. TEA blocks K+ channels and TTX blocks Na+ channelsi. Using TEA results in a short Na+ influxii. Using TTX results in a longer K+ efflux because these gates take longer to reach activation potentialV. Phases of the action potentiala. During the rising phase of the absolute refractory period the membrane is depolarizedi. The membrane is repolarized during the falling phase of the absolute refractory periodii. At this point after reaching the threshold it exhibits the all-or-none principleb. During the relative refractory period the membrane hyperpolarizesi. 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 hyperpolarizationc. Action potentials can be generated again as soon as gates are reset, even above the
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