NACS641-10L2 - Origin of the membrane potential and...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Origin of the membrane potential and propagation of electrical signals in neurons Ricardo C. Araneda [email protected] Fall 2010 Tuesday, September 14, 2010 OVERVIEW: * Origin of the membrane potential * The Nernst equation & GHK equation * Membranes as capacitors and ion channels as resistors (conductors) * The cell membrane as an electrical circuit * How do we measure signals from neurons Tuesday, September 14, 2010 The currency in the nervous system is electrical potentials (mV) Generator Action Synaptic potentials potentials potentials Evoked potentials Tuesday, September 14, 2010 Review of basic concepts Experiment 1 Cell membrane NaCl 10 mM in Tuesday, September 14, 2010 NaCl 100 mM out ◆Concentration Gradient Measure membrane potential Membrane potential=Vm Vm= Vin-Vout NaCl 10 mM NaCl 100 mM in Vout= 0 V Tuesday, September 14, 2010 ◆Concentration Gradient Vm = Vin Vm= ?? Measure membrane potential NaCl 10 mM Vin Tuesday, September 14, 2010 NaCl 100 mM V=0 Measure membrane potential NaCl 10 mM Vin NaCl 100 mM V=0 ◆Concentration Gradient ◆ Membrane is equally permeable to both Na and Cl Vm= ?? Tuesday, September 14, 2010 Measure membrane potential A membrane protein that is permeable to ions; ION CHANNEL NaCl 10 mM Vin NaCl 100 mM V=0 ◆Concentration Gradient ◆ Membrane is equally permeable to both Na and Cl Vm= ?? Tuesday, September 14, 2010 Membrane is selectively permeable to Sodium Cl _ in + Na _ Cl Cl Tuesday, September 14, 2010 Cl _ _ _ + Na + Na Cl _ Cl + Na Concentration Gradient + Na + Na out Cl + Na Cl _ + Na + Na Cl _ _ Membrane is selectively permeable to Sodium Cl _ + Na + Na out _ Cl + Na Cl + Na Cl Cl _ Cl _ _ _ + Na Concentration Gradient + Na Tuesday, September 14, 2010 in Cl + Na Cl _ + Na + Na Cl _ _ Membrane is selectively permeable to Sodium Cl + Na _ Excess of positive ions + _ Concentration Gradient Cl Potential difference Cl _ Cl + Na Na Cl + Na out Cl + Na Tuesday, September 14, 2010 in Cl - _ _ _ + Na Cl Excess of negative ions + Na + Na + Na Cl _ _ Membrane potential ◆Concentration Gradient across the membrane ◆Membrane is selectively permeable to ions The Nernst Equation VX = RT log [Xout] zF [Xin] NaCl 10 mM in NaCl 100 mM V=0 The Equation is valid only if the membrane is permeable to only one ion RT F ~ 58 at 20 C VNa = + 58 mV VCl = - 58 mV Tuesday, September 14, 2010 What is the sign of the Nernst potential?? Mg 2+ 2HPO Tuesday, September 14, 2010 Mg 2+ 2- HPO Membranes are permeable to more than one ion _ + + K Na + K + Na Cl Cl _ The Goldman-Hodgkin-Katz equation Permeability; how easy is for ions to cross the membrane Tuesday, September 14, 2010 Membranes as capacitors Cl _ Cl _ Cl + + Na + Na Na Internal conducting solution (ions) _ + + - External conducting solution (ions) Thin insulating layer (membrane, 4nm) Tuesday, September 14, 2010 Ion channels as resistors (conductors) + Na Internal conducting solution (ions) External conducting solution (ions) Ion channels Voltage-gated, NT-gated etc. Tuesday, September 14, 2010 Electrical model of the cell membrane Ion channel RESISTOR Tuesday, September 14, 2010 Membrane CAPACITOR The cell membrane as an electrical circuit Ionic membrane current Ii Capacitive membrane current Ic Membrane current = Im Tuesday, September 14, 2010 Im = I i + I c Effects of passing current on circuits containing R and C V changes instantaneously w ith I V changes linearly in time w ith I V changes exponentially w ith a time constant = RC Tuesday, September 14, 2010 RC circuits 37% of Vo (E and V are the same) For a rising exponential; -t/RC V = VO∗(1-e Tuesday, September 14, 2010 ) Experiment 2 Passing current and recording the membrane potential from a paramecium current-passing electrode recording electrode Negative current makes the membrane potential more negative hyperpolarization “electrotonic potential” Tuesday, September 14, 2010 Positive current makes the membrane potential more positive depolarization Linear relationship between current and voltage 20 current-passing electrode 15 Voltage (mV) recording electrode 10 5 0 0.05 “electrotonic potential” 0.1 0.15 Current (nA) V= I∗Rin Input Resistance Rin = 100 MΩ Tuesday, September 14, 2010 0.2 Measuring current and voltage in neurons electrons ions Tuesday, September 14, 2010 Measuring current and voltage in neurons Tuesday, September 14, 2010 ...
View Full Document

This note was uploaded on 09/21/2010 for the course NACS 641 taught by Professor Areneda during the Fall '10 term at University of Maryland Baltimore.

Ask a homework question - tutors are online