L3_NPB_101

L3_NPB_101 - Lecture3 OnlineHandouts Lec3Notes...

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: Lecture3 OnlineHandouts: Lec3Notes Announcements: None MembranePotenFal TheNeuron AcFonPotenFal Reading(Recommended): Reading:Ch4(pp8597) MembranePotenFal MembranePotenFal Plasmamembraneofalllivingcellshasa membranepotenFal(polarizedelectrically) SeparaFonofoppositechargesacrossplasma membrane DuetodifferencesinconcentraFonand permeabilityofkeyions UnequalDistribuFonofIons Fig.320,pg.75 MembranePotenFal Nerveandmusclecells Excitablecells Haveabilitytoproducerapid,transientchangesin theirmembranepotenFalwhenexcited ResFngmembranepotenFal ConstantmembranepotenFalpresentincellsof nonexcitableFsuesandthoseofexcitableFssues whentheyareatrest SupposeaconcentraFongradient existsforK+andA Let'smakethe membrane IMPERMEABLEtoA K+flowsoutofthe cell EK+ = -90 mV Plasma membrane ECF ICF Fig.320,pg.76 + TheEquilibriumPotenFalforK AconcentraFongradient pushesK+outofthecell Anelectricalgradientpulls K+backintothecell Forcesbalanceat equilibrium ElectrochemicalEquilibrium Ei(e.g.,EK+) Plasma membrane ECF ICF Electrical gradient for K+ Concentration gradient for K+ EK+ = 90 mV Fig.320,pg.76 EquilibriumPotenFalforNa+ Plasma membrane AconcentraFon gradientpushesNa+ intothecell Anelectricalgradient pullsNa+outofthe cell Forcesbalanceat equilibrium ENa+ Fig.321,pg.78 ECF Concentration gradient for Na+ ICF Electrical gradient for Na+ ENa+ = +60 mV RealCellsarePermeabletoSeveral Ions Plasma membrane K+flowsout Na+flowsin Clflowsin ECF ICF Relatively large net diffusion of K+ outward establishes an EK+ of 90 mV No diffusion of A across membrane Relatively small net diffusion of Na+ inward neutralizes some of the potential created by K+ alone Resting membrane potential = 70 mV (A = Large intracellular anionic proteins) Fig.322,pg.78 SodiumPotassiumChannels Fig.323,pg.79 TheNeuron ModelofaMammalianNeuron Fig.410,pg.94 Neuron Basicpartsofneuron(nervecell) Cellbody Dendrites Axon Neuron Cellbody Housesthenucleusandorganelles Dendrites Projectfromcellbodyandincreasesurfacearea availableforreceivingsignalsfromothernerve cells Signaltowardthecellbody Dendriteandcellbodyserveastheneuronsinput zone. Neuron Axon Nervefiber Single,elongatedtubularextensionthatconductsacFon potenFalsawayfromthecellbody ConducFngzoneoftheneuron Collaterals Sidebranchesofaxon Axonhillock FirstporFonoftheaxonplustheregionofthecellbodyfromwhich theaxonleaves Neuron'striggerzone Releasechemicalmessengersthatsimultaneouslyinfluenceother cellswithwhichtheycomeintocloseassociaFon Outputzoneoftheneuron Axonterminals NeuralCommunicaFon Membraneelectricalstates PolarizaFon AnystatewhenthemembranepotenFalisotherthan0mV DepolarizaFon MembranebecomeslesspolarizedthanatresFngpotenFal RepolarizaFon MembranereturnstoresFngpotenFalaeerhavingbeen depolarized HyperpolarizaFon MembranebecomesmorepolarizedthanatresFng potenFal BasicTerminology Repolarization Hyperpolarization Resting potential Depolarization Fig.41,pg.86 NeuralCommunicaFon TwokindsofpotenFalchange GradedpotenFals Serveasshortdistancesignals AcFonpotenFals Serveaslongdistancesignals AcFonPotenFals Brief,rapid,large(100mV)changesin membranepotenFalduringwhichpotenFal actuallyreverses InvolvesonlyasmallporFonofthetotal excitablecellmembrane Donotdecreaseinstrengthastheytravel fromtheirsiteofiniFaFonthroughout remainderofcellmembrane AnAcFonPotenFalMayOccurWhenEm DepolarizesPastThreshold = Action potential = After hyperpolarization Na+ equilibrium potential Threshold potential Resting potential Triggering event K+ equilibrium potential Fig.46,pg.90 AcFonPotenFals WhenmembranereachesthresholdpotenFal Voltagegatedchannelsinthemembraneundergo conformaFonalchanges FlowofsodiumionsintotheICFreversesthe membranepotenFalfrom70mVto+30mV FlowofpotassiumionsintotheECFrestoresthe membranepotenFaltotheresFngstate AcFonPotenFals AddiFonalcharacterisFcs SodiumchannelsopenduringdepolarizaFonby posiFvefeedback. WhenthesodiumchannelsbecomeinacFve,the channelsforpotassiumopen.Thisrepolarizesthe membrane. AstheacFonpotenFaldevelopsatonepointinthe plasmamembrane,itregeneratesanidenFcalacFon potenFalatthenextpointinthemembrane. Therefore,ittravelsalongtheplasmamembrane undiminished. TheAcFonPotenFalResultsfrom PosiFveFeedback Triggering event Depolarization (decreased membrane potential) Positive-feedback cycle Influx of Na+ (which further decreases membrane potential) Opening of some voltage-gated Na+ channels Fig.48,pg.92 AcFonPotenFalsareStereotypical What'sHappeningDuringanAcFon PotenFal? IonPermeabilityCHANGES x VoltageGatedNa+andK+Channels Caused a + influ Rising pha se d by N TheChangeOccursina TEMPORALMANNER Threshold potential Resting potential Falling phas + lux by K eff Cause Fig.49,pg.92 e SubThresholdResponses Graded potential (change in membrane potential relative to resting potential) Threshold! Resting potential Time Magnitude of stimulus Fig.42,pg.87 Stimuli applied OpeningofVoltageGatedNa+Channels DepolarizestheCell Voltage-Gated Sodium Channel Extracellular fluid (ECF) Plasma membrane Inactivation gate Activation gate Intracellular fluid (ICF) Rapid opening triggered at threshold Open (activated) From threshold to peak potential (50 mV to +30 mV) Slow closing triggered at threshold Closed and not capable of opening (inactivated) From peak to resting potential (+30 mV to 70 mV) Closed but capable of opening At resting potential (70 mV) Fig.47,pg.91 Na+InfluxDepolarizestheCellandOpens MoreVoltageGatedChannels Na+ activation gate opens At resting potential Threshold reached Action potential begins Depolarizing triggering event ImagesfromPhysioEdgeCD ThePeakoftheAcFonPotenFal Na+ inactivation gate begins to close Na+ inactivation gate begins to close K+ gate opens K+ gate opens Peak of action potential; potential reversed Peak of action potential; potential reversed ImagesfromPhysioEdgeCD +Channel TheVoltageGatedK Extracellular fluid (ECF) Plasma membrane Intracellular fluid (ICF) Thischannelalso openswith depolarizaFon Delayed opening triggered at threshold Open Closed At resting potential; delayed From peak potential through opening triggered at threshold; after hyperpolarization remains closed to peak potential (+30 mV to 80 mV) (70 mV to +30 mV) Abitslower Hasasingle acFvaFongate Fig.47,pg.91 RepolarizaFon Na+ inactivation gate opens; Na+ activation gate closes Repolarization begins Action potential complete; after hyperpolarization begins ImagesfromPhysioEdgeCD AeerhyperpolarizaFon a + influ x Caused se Falling phas d by N Rising pha + flux by K ef hyperpolarization is complete; return to resting potential Cause After e Threshold potential Resting potential ImagesfromPhysioEdgeCD Fig.49,pg.91 HowdoWeStopaPosiFveFeedback Process? Voltage-Gated Sodium Channel Extracellular fluid (ECF) Plasma membrane Inactivation gate Intracellular fluid (ICF) Rapid opening triggered at threshold Open (activated) From threshold to peak potential (50 mV to +30 mV) Slow closing triggered at threshold Closed and not capable of opening (inactivated) From peak to resting potential (+30 mV to 70 mV) Activation gate Closed but capable of opening At resting potential (70 mV) Fig.47,pg.91 AtAnyPointoftheAcFonPotenFal, TheEmisaFuncFonofPNa+ANDPK+ Absolute refractory period Relative refractory period Action potential Na+ permeability K+ permeability Fig.413,pg.97 ProperFesofVGatedChannelsAffectthe NeuronalFiringRate Absolute Relative refractory refractory period period RefractoryPeriods Action potential Na+ permeability AnewacFonpotenFal usuallycannotbeiniFatedin aregionthatjusthadan acFonpotenFal Why?InacFvaFonofthe populaFonofvoltagegated Na+channels K+ permeability Fig.413,pg.91 ProperFesofVGatedChannelsAffectthe NeuronalFiringRate Absolute Relative refractory refractory period period AbsoluteRefractoriness Action potential Na+ permeability AnewacFonpotenFal ABSOLUTELYcannotbe iniFatednomajerhowmuch sFmulaFonisgiven Why?Notenoughvoltage gatedNa+channelshave recoveredfrominacFvaFon K+ permeability Fig.413,pg.91 ProperFesofVGatedChannelsAffectthe NeuronalFiringRate Absolute Relative refractory refractory period period RelaFveRefractoriness Action potential AnewacFonpotenFal MIGHTBEiniFated ThesFmulusmustbe strongerthannormal Na+ permeability K+ permeability Fig.413,pg.91 ProperFesofVGatedChannelsAffectthe NeuronalFiringRate Absolute Relative refractory refractory period period RelaFveRefractoriness Action potential WHY?MorevoltagegatedNa +channelshaverecovered frominacFvaFon. BUT,ahyperpolarizing currentsFllflowsthroughthe voltagegatedK+channels. Na+ permeability K+ permeability Fig.413,pg.91 RefractoryPeriodsLimittheAcFon PotenFalFrequency Thisisimportantfortellingusthingssuchas sFmulusstrength(MORELATER) Briefly SFmuliofdifferingintensiFeselicitAPsinsensory neurons TheSTRONGERsFmulustriggersamoreAPsper second TheSIZEoftheAPwillNOTchange,regardlessthe sFmulusstrength. SoAPfrequencyisonewaytoencodeasignal TheMechanismof AcFonPotenFalPropagaFon AcFonPotenFalPropagaFon Active area at peak of action potential Adjacent inactive area into which depolarization is spreading; will soon reach threshold Remainder of axon still at resting potential Local current flow that depolarizes adjacent inactive area from resting to threshold Direction of propagation of action potential ImagesfromPhysioEdgeCD AcFonPotenFalPropagaFon Previous active area returned to resting potential Adjacent area that was brought to threshold by local current flow; now active at peak of action potential New adjacent inactive area into which depolarization is spreading; will soon Remainder of axon still at resting potential reach threshold ImagesfromPhysioEdgeCD ...
View Full Document

This note was uploaded on 04/17/2008 for the course NPB 101 taught by Professor Fuller,charles/goldberg,jack during the Spring '08 term at UC Davis.

Ask a homework question - tutors are online