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This 2 page Class Notes was uploaded by Maymie Gaylord on Monday September 21, 2015. The Class Notes belongs to BIOL 6102 at Georgia State University taught by Paul Katz in Fall. Since its upload, it has received 18 views. For similar materials see /class/209916/biol-6102-georgia-state-university in Biology at Georgia State University.
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Date Created: 09/21/15
July 16 2010 Biol 6102 Neurobiology Electrical Signaling Membrane Potential Chapter 3 Membrane Potential 0 Basis of cellular signaling Action Potential Synaptic Potential Terminology 0 Charge positive or negative and carried by ions units Coulom s 0 Voltage Potential a measure of how much charge is separated units Volts V Current I the flow of positive charge units Amperes Permeability the relative ease with which ions can flow through channels 0 Conductance G a measure ofthe ease with which charge can flow units Siemens S inverse of Resistance R units Ohms Q Method for recording Neuronal Membrane Potential Voltage Recording with intracellular microelectrodes records the potential difference across the membrane Physical basis for membrane potential 0 Separation of charge by the membrane 0 Differential concentrations of ions across membrane NaK pump maintains distribution 0 Selective Permeability to Na K Cl39 ions esting conductance Based on ion channels Nernst Equilibrium Potential 0 This is very importantlll The Equilibrium potential for an ion is the potential at which there is no net movement of an ion due to a balance between electrical and chemical O O gradients Rim X19 X ZF XL 0 Where EX Equilibrium Potential for ion X Xo is the concentration of ion X outside the neuron Xi is the concentration of ion X inside the neuron R Universal gas constant T Temperature in Kelvin Z Valence F Faraday constant Simplified Nernst Equation At 37 C RTF267mV The conversion of natural logarithm to base 10 logarithm is 23 E Q Io u x 2 g Xi Glial cells are very permeable to K but not permeable to other ions Therefore glial membrane potential is the same as EK o Vmem is determined by the ratio of Ko Ki p1 lf potential is across membrane is different than EX then a current will flow 0 Ix Gx vm Ex This isjust a variation of Ohm s law VR Ix is the current carried by the ion G is conductance to the ion Vm Ex is the driving force on the ion Neurons are permeable to more than just K so it is more complicated to determine their resting potentials based on ion concentrations Very Permeable to K Only slightly permeable to Na Influx of Na balanced by efflux of K Results in a resting potential slightly depolarized from EK Goldman Equation for predicting the membrane potential of a neuron v 62 log PKKo PNaNao PCI Cli PKKi PNaNai PCICIo Where V the membrane potential PX the permeability to ion X 0 At rest this approaches Nernst Equilibrium potential for K herefore membrane potential depolarizes if extracellular K is raised 0 At peak of action potential this approaches Nernst Equilibrium potential for Na Due to high permeability for sodium 0000 Ion Channels General Properties 0 Membrane spanning proteins Comprised of subunits or pseudosubunits hydrophobic amino acids 0 Ion selective due to properties ofthe pore region hydrophilic amino acids Neurons have an Ion Transporter Pump to redistribute Na and K Prevents the ionic gradients from dissipating o Requires ATP 0 Extrudes 3 Na for every 2 K it brings in p2
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