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UVM NSCI 110 - Membrane and Action Potentials
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NSCI 110 1st Edition Lecture 8 Outline of Last Lecture I. Schwann cells function in creating a healthful environment for axons and can provide myelination when necessaryII. Astrocytes function in maintaining extracellular concentrations, providing structural support, and linking neurons to the circulatory systemIII. Microglia are responsible for inflammatory responses in the brain and migrate to injuredbrain areasIV. Transmembrane protein channels allow passage of certain moleculesa. Leak channels b. Gated channelsc. Pumps Outline of Current 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 directionsCurrent LectureI. Every type of cell has a unique resting membrane potentiala. Varies from one type of neuron to another and across different speciesII. Hyperpolarization is a change in membrane potential that takes it from a starting value to a more negative valuea. How do you achieve hyperpolarization with a positive ion?i. The positive ion leaving creates a more negative space behind itIII. Depolarization is a change in membrane potential that takes it from a starting value to a less negative valueIV. Electrochemical gradient = ion diffusion + electrical gradientsa. Diffusion/concentration gradient (“force” pushing molecules)i. Ion flow doesn’t stop at equilibrium, it just occurs at equal ratesThese 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. Electrical gradient: net “+” and “–“ charges on each side of the membranec. Eion: membrane potential at which ion flux through the membrane is equal in both directionsi. All ions constitute a sort of “battery” that drives the electrical gradientV. Resting membrane potential (RMP)a. Four different key ionsi. Chloride (more concentrated outside cell)ii. Sodium (more concentrated outside cell)iii. Potassium (more concentrated inside cell)iv. Other anions (more concentrated inside cell)b. There is a net negative charge on the inside of the cell at resting potentiali. Measured as “Vm”VI. Ion channels consist of membrane spanning proteinsa. Membranes are porousb. Fundamental properties:i. Conductance: how easily ions flow through the channelii. Selective: recognize and select specific ions for conductanceiii. State: open or closed1. Gated channels can change state (conformation) to specific stimulic. Common types:i. Leak channelsii. Gated:1. Electrical2. Ligand3. Mechanical4. Phosphorylated d. Passive factorsi. Membrane permeability 1. Number of each type of leak channel2. Permeability of each typeii. Concentration gradients for sodium and potassiumiii. Electrical gradient across the membranee. Active factorsi. Active transporter or ion pumps1. ATP2. Sodium-potassium pump3. Some have a chloride pumpf. Collectively, all these factors constitute the resting membrane potential of an inactive neuron or neuron at restVII. More on resting membrane potentiala. Permeability is different for each ion (PK, PNa, PCl)i. The greater the permeability, the greater effect that ion has on resting potentialb. Also dependent on the area of the membranec. For RMP, most of the membrane is 30-50 times more permeable to potassium than sodiumi. Permeability mostly referring to the population of leak channels in the membraneii. RMP driven mostly by EK (about -80 mV)d. Equilibrium potential is the membrane potential (voltage) at which the flow of a specific ion through a membrane is equal or balanced in both directionsi. ENa, EK, EClii. Also, the balance between forces of the electrical and concentration gradientsiii. Also, when the pull of the electrical gradient exactly equals the pull of theconcentration gradient in the opposite direction across the membranee. Using the Nernst equationi. Your final answer equals the equilibrium


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UVM NSCI 110 - Membrane and Action Potentials

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