L5_NPB_101

L5_NPB_101 - Lecture5 OnlineHandouts: Lec4&5Notes...

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Unformatted text preview: Lecture5 OnlineHandouts: Lec4&5Notes Review AcEonPotenEal Announcements: None Reading(Required): Reading:Ch4(pp104108) Neurotransmi1ers& Neuromodulators AcEonPotenEal(cont'd) ConducEonofAP Synapse Reading(Recommended): Reading:Ch4(pp101111) REV:AcEonPotenEal 1. RapidstereotypedchangeinEm,whichoccursin responsetoasEmulus. 2. Thereare6primarycharacterisEcsofanAP: a) LargeregeneraEveincreaseinPNaviaPosiEve Feedback b) RapidrepolarizaEonofEmbyslowincreaseinPK c) EveryAPfollowedby2refractoryperiods d) EveryAPisAllorNone e) APconductedovertheaxon f) APareconductedrapidly AtAnyPointoftheAcEonPotenEal, TheEmisaFuncEonofPNa+ANDPK+ Absolute refractory period Relative refractory period Action potential Na+ permeability K+ permeability Fig.413,pg.97 VoltageGatedChannelProperEesAffectthe NeuronalFiringRate Absolute Relative refractory refractory period period RefractoryPeriods Action potential Na+ permeability AnewacEonpotenEal usuallycannotbeiniEatedin aregionthatjusthadan acEonpotenEal Why?InacEvaEonofthe populaEonofvoltagegated Na+channels K+ permeability Fig.413,pg.97 VoltageGatedChannelProperEesAffectthe NeuronalFiringRate Absolute Relative refractory refractory period period AbsoluteRefractoryPeriod Action potential Na+ permeability AnewacEonpotenEal ABSOLUTELYcannotbe iniEatednomaferhowmuch sEmulaEonisgiven Why? NotenoughvoltagegatedNa+ channelshaverecoveredfrom inacEvaEon K+ permeability Fig.413,pg.97 VoltageGatedChannelProperEesAffectthe NeuronalFiringRate Absolute Relative refractory refractory period period RelaEveRefractoryPeriod Action potential AnewacEonpotenEal MIGHTBEiniEated ThesEmulusmustbe strongerthannormal Na+ permeability K+ permeability Fig.413,pg.97 VoltageGatedChannelProperEesAffectthe NeuronalFiringRate Absolute Relative refractory refractory period period RelaEveRefractoryPeriod WHY? Action potential Na+ permeability MorevoltagegatedNa+ channelshaverecoveredfrom inacEvaEon. K+ permeability BUT, ahyperpolarizingcurrentsEll flowsthroughthevoltagegated K+channels. Fig.413,pg.97 RefractoryPeriodsLimitAPFrequency Thisisimportantfortellingusthingssuchas sEmulusstrength(MORELATER) Briefly SEmuliofdifferingintensiEeselicitAPsinsensory neurons TheSTRONGERsEmulustriggersamoreAPsper second TheSIZEoftheAPwillNOTchange,regardlessthe sEmulusstrength(RememberAPisstereotypical). SoAPfrequencyisonewaytoencodeasignal ConducEonofAcEonPotenEal AcEonPotenEalPropagaEon 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 AcEonPotenEalPropagaEon 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 ConducEonVelocity(CV)ofAP TwotypesofpropagaEon ConEguousconducEon ConducEoninunmyelinatedfibers AcEonpotenEalspreadsalongeveryporEonofthe membrane SaltatoryconducEon RapidconducEoninmyelinatedfibers ImpulsejumpsoversecEonsofthefibercoveredwith insulaEngmyelin ConEguousConducEon Fig.412,pg.97 ConducEonVelocity 3factorsaffectAPConducEonVelocity(CV) Axonresistance: o o diameter leaks CV CV resistance CV Membrane(Current)leaks: Membranecapacitance(abilitytostorecharge): o capacitance SaltatoryConducEon Fig.414,pg.99 SaltatoryConducEon PropagatesacEonpotenEalfasterthan conEguousconducEonbecauseacEonpotenEal doesnothavetoberegeneratedatmyelinated secEon Myelinatedfibersconductimpulsesabout50 Emesfasterthanunmyelinatedfibersof comparablesize Myelin Primarilycomposedoflipids FormedbyoligodendrocytesinCNS FormedbySchwanncellsinPNS CurrentFlowinUnmyelinatedand MyelinatedAxons "Smallsteps" Saltatory conducEon TheSynapse AxonCommunicaEon MorphologyofaChemicalSynapse Synaptic inputs (presynaptic axon terminals) Input Zone Dendrites and Cell body Nucleus Trigger Zone Axon hillock Conducting Zone Axon (may be from 1mm to more than 1m long) Dendrites Cell body of postsynaptic neuron Axon hillock Axon Arrows indicate the direction in which nerve signals are conveyed. Output Zone Axon terminals Myelin sheath Fig.410a,pg.94 Fig.415,pg.102 SynapEcConvergenceandDivergence Presynaptic inputs Convergence of input (one cell is influenced by many others) Postsynaptic neuron Presynaptic inputs Divergence of output (one cell influences many others) Postsynaptic neurons Arrows indicate direction in which information is being conveyed. Fig.420,pg.111 Synapses JuncEonbetweentwoneurons Primarymeansbywhichoneneurondirectlyinteracts withanotherneuron GeneralAnatomyofasynapse Presynap7cneuronconductsacEonpotenEaltoward synapse SynapEcknobcontainssynapEcvesicles SynapEcvesiclesstoresneurotransmifer(carriessignalacrossa synapse) Postsynap7cneuronneuronwhoseacEonpotenEalsare propagatedawayfromthesynapse Synap7ccle:spacebetweenthepresynapEcand postsynapEcneurons GeneralSynapse AP SYNAPTICCLEFT Fig.416a,pg.103 POSTSYNAPTICCELL AnatomyofaChemicalSynapse Presynaptic axon terminal Voltage-gated Ca2+ channel Synaptic knob Ca2+ Neurotransmitter molecule Synaptic vesicle Synaptic cleft Subsynaptic membrane Chemically gated ion channel for Na+, K+, or ClReceptor for neurotransmitter Postsynaptic neuron Fig.416a,pg.103 SynapsePhysiology SynapEctransmission ProcessofconversionofelectricalAPinformaEon intochemicalEmchangeinpostsynapEccell. Occursin8steps 1) AxonAPdepolarizesAxonterminal. 2) Ca+2permeabilityincreasedbyopeningvoltage sensiEveCa+2channels(ECaisPosiEveEm). 3) ChemicalNeurotransmiferreleasedasCa+2incell leadstofusionofsynapEcvesiclestopresynapEc membraneandexocytosisofvesicles. SynapsePhysiology(cont'd) 4) DiffusionofNTacrosssynapEcclep. Release/diffusiontakeEme(~0.5mSec);synapEcdelay. 5) NTbindstoreceptorsinpostsynapEcmembrane. 6) PostsynapEcresponse: open/closechemicallygatedionchannels. increase/decreaseionpermeability. Increase/decreaseionflowthroughpostsynapEcmembrane. Quantal/gradedresponsenotallornone. 7) 2basictypesofresponseExcitatory&Inhibitory 8) RemovalofNTfromsynapEcclepspecialized mechanismslimitamountofEmeNTispresent. TheChemicalSynapse Presynaptic axon terminal Voltage-gated Ca2+ channel Synaptic knob Ca2+ Neurotransmitter molecule Synaptic vesicle Synaptic cleft Subsynaptic membrane Chemically gated ion channel for Na+, K+, or Cl- Postsynaptic neuron Fig.416a,pg.103 Receptor for neurotransmitter PresynapEcandPostsynapEcMembranes Vesicularfusionand NTrelease NTdiffusion BindingapostsynapEc receptor Ionflow Fig.416b,pg.103 Neurotransmifers Varyfromsynapsetosynapse SameneurotransmiferisalwaysreleasedataparEcularsynapse QuicklyremovedfromthesynapEcclep Somecommonneurotransmifers Acetylcholine Dopamine Norepinephrine Epinephrine Serotonin Histamine Glycine Glutamate Aspartate Gammaaminobutyricacid(GABA) SynapEcPotenEals Signalatsynapseeitherexcites(+)orinhibits ()thepostsynapEcneuron SigndependsupondirecEonofEmchange EisdepolarizaEonclosertoThreshold IishyperpolarizaEonfartherfromThreshold Twotypesofsynapses Excitatorysynapses Inhibitorysynapses ExcitatoryPostsynapEcPotenEals EPSP:cellmoreexcitable NTopensachemically gatednonspecificcaEon channel. IncreasePNaandPK GreatertendencyforNa+ toentercell(rememberEi) ResultsindepolarizaEon SmallchangeinEm GradedpotenEal Fig.417a,pg.104 InhibitoryPostsynapEcPotenEals IPSP:celllessexcitable NTopensachemically gatednonspecificK+orCl channel. IncreasePKorPCl GreatertendencyforK+to leavecellorCltoentercell (rememberEi) ResultsinhyperpolarizaEon SmallchangeinEm GradedpotenEal Fig.417b,pg.104 SummaEonofSynapEcInput Excitatory presynaptic inputs Recording potential of postsynaptic cell Temporal summation Spatial summation EPSPIPSP cancellation Recording potential of postsynaptic cell Inhibitory presynaptic input Threshold potential Resting potential Fig.418,pg.106 SummaEonofSynapEcInput MorphologyofanElectricalSynapse Cell 1 cytosol Cell 2 cytosol Connexon Gap junction Diameter of channel = 1.5 nm Longitudinal section of connexon Passage of ions and small molecules No passage of large molecules 24 nm Interacting plasma membranes Fig.36,pg.60 ...
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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.

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