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 necessary II Astrocytes function in maintaining extracellular concentrations providing structural support and linking neurons to the circulatory system III Microglia are responsible for inflammatory responses in the brain and migrate to injured brain areas IV Transmembrane protein channels allow passage of certain molecules a Leak channels b Gated channels c Pumps Outline of Current 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 Current Lecture I Every type of cell has a unique resting membrane potential a Varies from one type of neuron to another and across different species II Hyperpolarization is a change in membrane potential that takes it from a starting value to a more negative value a How do you achieve hyperpolarization with a positive ion i The positive ion leaving creates a more negative space behind it III Depolarization is a change in membrane potential that takes it from a starting value to a less negative value IV Electrochemical gradient ion diffusion electrical gradients a Diffusion concentration gradient force pushing molecules i Ion flow doesn t stop at equilibrium it just occurs at equal rates 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 V VI VII b Electrical gradient net and charges on each side of the membrane c Eion membrane potential at which ion flux through the membrane is equal in both directions i All ions constitute a sort of battery that drives the electrical gradient Resting membrane potential RMP a Four different key ions i 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 potential i Measured as Vm Ion channels consist of membrane spanning proteins a Membranes are porous b Fundamental properties i Conductance how easily ions flow through the channel ii Selective recognize and select specific ions for conductance iii State open or closed 1 Gated channels can change state conformation to specific stimuli c Common types i Leak channels ii Gated 1 Electrical 2 Ligand 3 Mechanical 4 Phosphorylated d Passive factors i Membrane permeability 1 Number of each type of leak channel 2 Permeability of each type ii Concentration gradients for sodium and potassium iii Electrical gradient across the membrane e Active factors i Active transporter or ion pumps 1 ATP 2 Sodium potassium pump 3 Some have a chloride pump f Collectively all these factors constitute the resting membrane potential of an inactive neuron or neuron at rest More on resting membrane potential a Permeability is different for each ion PK PNa PCl i The greater the permeability the greater effect that ion has on resting potential b Also dependent on the area of the membrane c For RMP most of the membrane is 30 50 times more permeable to potassium than sodium i Permeability mostly referring to the population of leak channels in the membrane ii 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 directions i ENa EK ECl ii Also the balance between forces of the electrical and concentration gradients iii Also when the pull of the electrical gradient exactly equals the pull of the concentration gradient in the opposite direction across the membrane e Using the Nernst equation i Your final answer equals the equilibrium potential
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