the resting potential (rp) -：静息电位（rp）—

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1、Dr.AnnE.Stuart966-0272;stuart@med.unc.eduSIMULATING(1)ASTATIONARYAPINANORMALAXONAND(2)APROPAGATINGAPINANAXONAFFECTEDBYMULTIPLESCLEROSISThepatch(stationary)actionpotentialsimulationQ.1.Decreasethe[Na]outtotrytomakeENamovetowardszeroandthepeakoftheAPgetsmaller.(NotethatthepeakoftheA

2、PdoesnotquitereachENabecausetheKconductanceisstartingtobringitbackdown).Think--Atwhatvalueof[Na]outwillENaequalzero?Seeifyouwerecorrect.[Na]out=????ENa=0=58log----------------------[Na]out=_______mM[Na]in=14mMQ.2.Increasethe[K]outandwatchwhathappenstoEkandtothefallingphase(repolar

3、ization)oftheAP.IncreaseitsomuchthatEkbecomespositive.Nowincreaseitaridiculousamount—say,to2000mM—andwatchwhathappenstothe“fallingphase”oftheAP.Whatdoyouconclude?(a)ThefallingphaseinunaffectedbyEk.(b)ThefallingphaseoftheAPgoestowhereEkis.(c)TheAPfails.Q.3.WhathappenstotheAPasthene

4、rvegetscolder?(a)ThepeakoftheAPgetssmaller(b)ThedurationoftheAPgetslonger(c)TheAPfailsThepropagatingactionpotentialsimulationinapartiallydemyelinatedaxon.Using“Continuefor”(seeinstructions),stoptheAPabouthalfwaydownthebareaxon,drawit,andlabel3importantphasesoftheAP:therisingphase(

5、the“front”oftheAP,thepeak,andthe“fallingphase”(the“back”oftheAP).RememberthatthisAPisplottedasafunctionofspace,nottime.Q.4.Whereisthe“front”ofthisAP(therisingphase)?(a)Right-handportionoftheAP(b)Left-handportionoftheAPQ.5.WheredoestheinwardNacurrentgreatlyexceedtheoutwardKcurrent?

6、(a)Right-handportionofAP(b)Left-handportionofAPQ.6.WheredoestheoutwardKcurrentgreatlyexceedtheinwardNacurrent?(a)Right-handportionofAP(b)Left-handportionofAPQ.7.Onwhichportionofthewaveformwouldyouexpectthethresholdtobe?(a)Right-handportion(b)Left-handportionStoptheAPwhenitspeakisi

7、nthebareaxonandthenagainwhenitisinvadingthemyelinatedportionandmeasuretheapproximatelengthofaxon(inmicrons)thatisreversedinpolarity(insidepositive)atanyonetime.ThelengthofaxonwherethepotentialisreversedgivesagoodfeelingforhowspreadouttheAPisintheaxonandthushowfastitistraveling.Q.8

8、.Abouthowmuchoftheaxonhasreversed