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UCSD BILD 2 - Lecture

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LE 48-5DendritesCell bodyNucleusAxon hillockAxonSignaldirectionPresynaptic cellMyelin sheathSynapticterminalsSynapsePostsynaptic cellLE 48-9MicroelectrodeReferenceelectrodeVoltagerecorder–70 mVLE 48-10CYTOSOL EXTRACELLULARFLUID[Na+]15 mM[K+]150 mM[A–]100 mM[Na+]150 mM[K+]5 mM[Cl–]120 mM[Cl–]10 mMPlasmamembraneLE 7-16 Cytoplasmic Na+ bonds tothe sodium-potassium pumpCYTOPLASMNa+[Na+] low[K+] highNa+Na+EXTRACELLULARFLUID[Na+] high[K+] lowNa+Na+Na+ATPADPP Na+ binding stimulatesphosphorylation by ATP.Na+Na+Na+K+ Phosphorylation causesthe protein to change itsconformation, expelling Na+to the outside.P Extracellular K+ bindsto the protein, triggeringrelease of the phosphategroup.PP Loss of the phosphaterestores the protein’soriginal conformation. K+ is released and Na+sites are receptive again;the cycle repeats.K+K+K+K+K+LE 48-11150 mMKClInnerchamberOuterchamber–92 mVPotassiumchannelMembrane selectively permeable to K+Membrane selectively permeable to Na+5 mMKClArtificialmembraneK+Cl–150 mMNaClInnerchamberOuterchamber+62 mVSodiumchannel15 mMNaClNa+Cl–LE 48-12HyperpolarizationsGraded potential hyperpolarizations Graded potential depolarizations5Time (msec)Restingpotential43210Threshold–100–500Membrane potential (mV)Stimuli+50Depolarizations5Time (msec)Restingpotential43210Threshold–100–500Membrane potential (mV)Stimuli+50Action potential5Time (msec)Restingpotential43210Threshold–100–500Membrane potential (mV)Stronger depolarizing stimulus+50Actionpotential6LE 48-13_5Resting potentialThresholdMembrane potential(mV)ActionpotentialTime–100–50+500PotassiumchannelExtracellular fluidPlasma membraneNa+Resting stateInactivationgateActivationgatesSodiumchannelK+CytosolNa+DepolarizationK+Na+Na+Rising phase of the action potentialK+Na+Na+Falling phase of the action potentialK+Na+Na+UndershootK+Na+LE 48-14cAn action potential is generated as Na+ flows inwardacross the membrane at one location.Na+Action potentialAxonNa+Action potentialK+The depolarization of the action potential spreads to theneighboring region of the membrane, re-initiating theaction potential there. To the left of this region, themembrane is repolarizing as K+ flows outward.K+Na+Action potentialK+The depolarization-repolarization process is repeated in thenext region of the membrane. In this way, local currents ofions across the plasma membrane cause the action potentialto be propagated along the length of the axon.K+• After the depolarization of an action potential,repolarization occurs due to the– A. closing of sodium activation and inactivationgates.– B. opening of sodium activation gates.– C. refractory period in which the membrane ishyperpolarized.– D. delay in the action of the sodium-potassiumpump.– E. opening of voltage-gated potassium channelsand the closing of sodium channels.LE 48-8AxonNodes ofRanvierSchwanncellMyelin sheathNucleus ofSchwann cellSchwanncellNodes of RanvierLayers of myelinAxon0.1 µmLE 48-15Cell bodySchwann cellDepolarized region(node of Ranvier)MyelinsheathAxon2. How is an increase in the strength of a stimuluscommunicated by a neuron?– A. The spike of the action potential reaches a highervoltage.– B. The frequency of action potentials generated alongthe neuron increases.– C. The length of an action potential (the duration of thedepolarization phase) increases.– D. The action potential travels along the neuron faster.– E. All action potentials are the same; the nervous systemcannot discriminate between different strengths


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UCSD BILD 2 - Lecture

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