Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane...

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Action Potential Lesson 12

Transcript of Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane...

Page 1: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

ActionPotentialLesson12

Page 2: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

LearningGoals

1. Whatisanactionpotential

2. Howdoeselectricalimpulsemoveacrossaneuron

Page 3: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

Actionpotential

Actionpotential• Atemporaryshiftinthemembranepotential• Resultsfromthevoltagedifference acrossamembranewhenthenerveisexcited• Theelectricalcurrent(impulse)travelsthelengthofanaxon

Membranepotential(voltage)• Differences inelectricalpotentialacrossamembrane(chargeseparation)• Unequalsodium(Na+)andpotassium(K+)ionsinsideandoutsidethecell

Page 4: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

MembraneRestingpotential(MRP)

•Membranepotentialofaneuronatrest (-70mV)

Sodium-potassiumpump• Activetransportthatmoves3Na+outofthecelland2K+intothecellacrosstheirconcentrationgradients

Page 5: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

RestingMembranePotential

• Atrest,themembraneinside aneuronhasanegative charge

• Atrest,outside oftheneuronmembraneispositively charged

Page 6: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

Axonhillock

AxonHillock• Specializedpartofthecellbodythatconnectsittotheaxon• Thesitewheretheaxonbegins

Page 7: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

Thresholdlevel

• IncomingNa+fromastimulusraisesmembranepotentialuntilitreachesthethresholdpotentialof-50 to-55mV

Thresholdlevel• Minimumlevelofastimulus

requiredtoproducearesponse(depolarization)

• Causeallvoltage-gatedNa+channelstoopen

Page 8: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

ActionPotential

• Themagnitudeofapotentialstaysthesameasittravelsalonganaxon• Theall-or-nothingcharacteristicoftheAPmeansthattheintensityorstimulusisreflectedinthefrequencyofAPratherthanintheirmagnitude

• Thegreaterthestimulus,thefastertheAP

Page 9: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

Depolarization

Depolarization• Diffusionofsodiumionsintothenervecellresultinginachargereversal• Insidethecellbrieflybecomespositive

Page 10: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

Repolarization

• Whenthemembranepotentialreaches+30mV,theNa+voltage-gatedionchannelsclose

Repolarization• Processofrestoringtheoriginalpolarityofthenervemembrane

• K+voltage-gatedchannelsopenandK+ionsexitalongitsconcentrationgradient

• Depolarizationandrepolarizationonlytakesabout5milliseconds!

Page 11: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

Hyperpolarization

Hyperpolarization• Processofrestoringtheoriginalpolarityofthenervemembrane• K+channelscloseslowly =K+outflow=-80mV

RefractoryPeriod• Recoverytime requiredbeforeaneuroncanproduceanotheractionpotential• Thresholdtodepolarizetheneuronishardertoreach

Page 12: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

RestingMembranePotential

• Na+/K+pump returnstheneurontorestingpotential

• Neuronisreadyforanewactionpotential

Page 13: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

“All-or-Nothing”response

• Anactionpotentialisonlyproducedifthestimulusisstrongenoughtocausedepolarizationatthethresholdlevel(-55mV)

• Neuronswillfiremaximallyornotatall

• Intensityofimpulseandspeedoftransmissionisindependent ofstimulusstrengthoncethresholdisreached

Page 14: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

ActionPotentialPropagation

• Depolarizationofonesitecausesnearbyvoltage-gatedNa+channelstoopenà resultingindepolarizationofanadjacentsite

• Actionpotential“travels”byrepeatedregenerationalongaxon

• Refractoryperiodensurestheactionpotentialtravelsinonedirectiononly =unidirectional

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SpeedofTransmission?

Axondiameter

• Larger=fasterconduction• Lessresistance

Myelination(myelinsheath)

• Voltage-gatedionchannelsonlyinnodesofRanvier• Axonsonlyexposedtoionsinextracellularfluid(ECF)nodes• Noactionpotentialinregionsbetweennodes

Page 16: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

UnmyelinatedConduction

Page 17: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

MyelinatedConduction

• Currentgeneratedbyactionpotentialatanode“leaps”tonextnode

• Na+andK+exchangecanonlyoccurwheretheaxonsareexposedtotheECF

• Allowsforfastersignalconductionalongtheaxon

Page 18: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

Synapse

• Asmallregionthatcontrolscommunicationbetweentwoneuronsorbetweenneuronsandeffectors

• Actionpotentialistransmittedthroughthesynapsebyneurotransmitters thatarereceivedbyreceptors ontheothersideofthesynapse

• Neurotransmitters=chemicalmessengers containedinvesicles• Releasedfromthepresynapticneuron

anddepolarizesthepostsynapticneuron

• Moresynapses=slowertransmission• Veryfewsynapsesinareflexarc,butMANYinvolvedinproblemsolving!

Page 19: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

ActionPotential

• Themagnitudeofapotentialstaysthesameasittravelsalonganaxon• Theall-or-nothingcharacteristicoftheAPmeansthattheintensityorstimulusisreflectedinthefrequencyofAPratherthanintheirmagnitude

• Thegreaterthestimulus,thefastertheAP

ActionPotentialSummary

Page 20: Lesson 2.15 - Action Potential (PPT) · 2019-10-26 · Membrane Resting potential (MRP) •Membrane potential of a neuron at rest(-70 mV)Sodium-potassium pump •Active transport

Homework

1. Worksheetquestions

2. UnitTaskResearch:DueTuesday• ComputerlabwillbeopenonMondayatlunch

3. Reproductive(female)assignment:DueMonday


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