Anatomy and phys lecture 15
Anatomy and phys lecture 15 PHCL2600
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This 6 page Class Notes was uploaded by Legacy Tanner on Tuesday October 6, 2015. The Class Notes belongs to PHCL2600 at University of Toledo taught by Williams,F in Fall 2015. Since its upload, it has received 30 views. For similar materials see Funct Anat and Pathophysiol I in Pharmaceutical Sciences at University of Toledo.
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Date Created: 10/06/15
Anatomy Lecture 15 Resting membrane potential RMP O RMP is measured at rest neuron is not conducting a nerve impulse Buildup of equal numbers of negative and positive ions in opposite side of the membrane Buildup of charge occurs only very close to the membrane Cytosol elsewhere in the cell is electrically neutral Different ion concentrations across the plasma membrane RMP in neurons depends mainly on K and Na Inside the neuron K is high charge is balanced by negatively charged ions and proteins Outside the neuron Na is high Na is balanced by high Cl Membrane potential Pic in phone Why an electrical potential is generated Pic in phone Nernst equation Equilibrium potential electrochemical potential generated at equilibrium can be predicted by the Nernst equation 0 E ion RTzF x lnionoioni o E equilibrium potential mv o R universal gas constant 831 Jmol x Kelvin o F faraday 96500 Coulombs mole charge o T temp of solution 310 Kelvin 0 Z valence 0 Pic in phone 0 O is outside and l is inside Calculation of equilibrium potential for speci c ion 0 Pic in phone 0 Numbers represent the membrane potential at which each ion comes to equilibrium equilibrium potential for the ions 0 Many ions contribute to membrane potential It mainly depends on distribution of K Cl Na Goldman eld equation is used to describe the membrane potential It considers concentrations of ion insideoutside cell and permeability p of membrane to each ion Pic in phone of equation 0 is outside and l is inside Rule the membrane potential at any time is closest in value to the equilibrium potential for the ions to which the membrane is most permeable Em neuron 70mv 0 Measurement of membrane potential All cells in the relaxed state have a resting membrane potential Em skeletal muscle 90mv Em neuron 70mv Em RBC 7mv to 14 mv A voltmeter was placed in the membrane of these cells to calculate the voltage of the ions as the charge changed 0 What do we need to maintain RMP Voltagegated channels are in a resting state so we need all channels but these because resting membrane potential doesn t have a change in charge so the voltagegated channels wouldn t be opening We can use K leak channels Na leak channels and NaK ATPase channels 0 How is the RMP maintained At rest the neuron is highly permeable to K At 70mv resting potential K leaks out of cell Na is less permeable but a small amount leaks into the neuron Neuron must compensate for K and Na leaks NaK ATPase maintains the resting membrane potential 0 Transport 3 Na out and 2 K in hydrolysis of ATP 0 Action potential A signal which travels the length of the neuron During an AP the membrane potential reverses and then eventually is restored to its resting state 0 Exchange of ions across the membrane Characteristics of action potential 0 Action potential depends on 0 Distribution of ions 0 Changes in membrane permeability toions Mainly Na and K CI to a lesser degree Action of voltagegated channels o It is a shortlasting event 0 An action potential has 2 main phases 0 Pic in phone 0 Has depolarizing phase and repolarizing phase 2 main phases 0 Another phase is hyperpolarization 0 During resting state Voltagegated Na channels are in resting state Voltagegated K channels are closed Na and K pump fully involved o Depolarization phase 2 Voltagegated Na channels starting to open Depolarization needs to reach a certain level or threshold 55mv to produce an action potential Depolarization is a shift from the resting membrane potential toward a more positive potential Charges change across the membrane 0 Generation of action potential Action potential will have the same amplitude Independent on stimulus intensity Pic in phone 0 Depolarization phase 3 After the membrane reaches threshold Voltagegated Na channels open 0 Channel activation gates open Na rushes into the neuron Building of more positive charges inside of the cell next to membrane As membrane potential approaches 30mv the inactivation gate of the voltage gated Na channels close in most channels 0 Beginning of repolarization phase Repolarizing phase begins Na channel inactivation gates close and K channels open Membrane starts to become repolarized as some K ions leave neuron and few negative charges begin to build up along inside surface of membrane Repolarization is the process of restoring the normal resting membrane potential after depolarization Na channels inactivation gates close