Silicon for computer chips is grown in large cylinders called "boules" that are in diameter and in height. The density of silicon is . Silicon wafers for making integrated circuits are sliced from a boule and are typically thick and in diameter. (a) How many wafers can be cut from a single boule? (b) What is the mass of a silicon wafer? (The volume of a cylinder is given by , where is the radius and is its height.)

NervousSystem:TheFundamentalsPart2 4/10/1610:29PM RestingMembranePotential • Restingmembranepotentialliesataround-70mV • Differenceinelectricalchargeacrossthemembrane • Alwaysnegative • Insideofthecellismorenegativethatoutside RoleofIonChannelsInMembranePotential • Leakychannelsarealwaysopen • Gatedchannelsarenotalwaysopen • VoltageGatedchannelsonlyopeninresponsetoavoltagechange TwoFactorsContributetoRMP • Concentrationgradient:ionswillmovedowntheirconcentrationgradient • Electricalgradient:ionswillmovedowntheirelectricalgradient • Balancebetweenthetwoistheelectrochemicalgradient • IonConcentrationinRMP • Moresodiumontheoutsideandmorepotassiumontheinsideofthecell • RoleofPlasmaPermeabilityinRMP • Notpermeabletoproteinanions • VerylittleNa+ispermeable • MostlypermeabletoK+ions • K+andNa+contributemosttoRMP • WhathappenstodisruptRMP • Gradedpotentialswhichoccurindendritesandareincomingsignals(varyinstrength) • Actionpotentialsoccurinaxonsandareoutgoingsignals(allornothing) • ChangesinPolarity • Depolarization:membranepotentialismorepositive • Hyperpolarization:membranepotentialismorenegativethanresting • Repolarization:membranepotentialismorenegativeafterdepolarization • GradedPotentials • Shortandlocalized • Magnitudeanddistancearedeterminedbythestrengthofthestimulus • TwoInstancesofGradedPotentials • ReceptorPotentialorGeneratorPotential:whenasensoryneuronfires • PostsynapticPotential:whenanaxonmeetswiththedendritesofanotherneuron • Axosomatic,axoaxonal,axodendriticsynapses • ActionPotentials • 1.RestingState:nomembranepotentialchange • 2.Na+flowsintothecellbecausethevoltagegatedchannelshaveopened • 3.Repolarization:sodiumchannelsclose,andpotassiumchannelsopen,allowing potassiumtoflowoutofthecell • 4.K+ionscontinuetoleavethecellcausinghyperpolarization • 5.Sodiumpotassiumpumprestoresrestingmembranepotential • Threshold • Actionpotentialsdonotoccurifvoltagedoesnotreach-55mV • Notalldepolarizationscauseactionpotentials • PropagationofActionPotentials • Localvoltagechangecausessodiumchannelstoopen • Thoseopenchannelscausethesodiumchannelsfurtherdowntheneurontoopen • Thishappensallthewaydowntheneuron • Strongerstimuliresultinmoreactionpotentials • RefractoryPeriods • Timewhenanotheractionpotentialcan’thappen • Absolute:actionpotentialwillnotoccur,regardlessofstimulusstrength • Relative:actionpotentialwillonlyoccurwithasuperstrongstimulus • HowFastDoActionPotentialsTravel • Factors:diameterofaxonandamountofmyelination • RoleofMyelinationinActionPotentialVelocity • Innon-myelinatedaxons,actionpotentialshavetoconstantlyregenerate,so conductionisslow • Inmyelinatedaxons,themyelinsheathhousesareasoftheaxonwithnoleakychannels, meaningthevoltageoftheactionpotentialdoesnotdecayasittravels.Thisleadstofast conduction • MultipleSclerosis • Whitebloodcellsattackmyelin • Causespoornervesignaling • Mostlyseeninwomen 4/10/16 10:29 PM 4/10/16 10:29 PM