andrew allen - studentvip · andrew allen neur30002 neurophysiology: neurons and circuits 2...
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AndrewAllen
NEUR30002Neurophysiology:NeuronsandCircuits
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CellularComponentsoftheBrain
Thenervoussystemconsistsofseveraltimesmoregliathanneurons.
AstrocytesThe number of astrocytes per neuron of the CNS of an organism is proportional to the
complexityoftheCNSoftheorganism.
Astrocytesareinvolvedininformationprocessing.
SpatialBufferingGapjunctionsconsistoftwoconnexons,whicheachconsistofsixconnexins.
Astrocytes take up potassium, which is released by active neurons, and dissipates it
throughoutneighbouringastrocytesviagapjunctions.
Astrocytes can transmit electrical and chemical signals toneighbouringastrocytes via gap
junctions.
ResponsiveAstrocytesAstrocytescanrespondtostimulationbyactivatingintracellularcalciumviaIP3.
Inresponsetostimulation,astrocytescanreleasegliotransmitters,whichcanstimulateother
astrocytes,bycalcium-dependentexocytosis.
Glialcellsofthenervoussystem.
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Astrocytic responses to stimulation by glutamate
(http://www.sciencedirect.com.ezp.lib.unimelb.edu.au/science/article/pii/S0166223603002376).
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RestingMembranePotentialTherestingmembranepotentialofatypicalneuronis−65%&.
Extracellular and Intracellular Ion Concentrations and EquilibriumPotentialsPotassiumtypicallyhasanECFconcentrationof5%',anICFconcentrationof150%',and
anequilibriumpotentialof−90%&.
SodiumtypicallyhasanECFconcentrationof150%',anICFconcentrationof10%',and
anequilibriumpotentialof+60%&.
ChloridetypicallyhasanECFconcentrationof100%',anICFconcentrationof10%',and
anequilibriumpotentialof−60%&.
CalciumtypicallyhasanECFconcentrationof1%',andanICFconcentrationof0.0001%',
andanequilibriumpotentialof+120%&.
IonTransportersandIonChannelsIon transportersmove ionsagainst theirconcentrationgradient,andcreateconcentration
gradients.
IonPumpsIonpumps,suchassodium-potassiumpumpsandcalciumpumps,areiontransporters.
Sodium-potassiumpumpsmovethreesodiumionsoutofacellandtwopotassiumionsinto
a cell per molecule of ATP, and are primarily responsible for creating the sodium and
potassiumconcentrationgradientsofcells.
Sodium-potassium pumps consist of an alpha subunit that has an Ouabain binding site, a
phosphorylationsite,asodiumbindingsite,apotassiumbindingsite,andanATPbindingsite,anda
betasubunit.
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IonExchangersIonexchangersareiontransporters,andmoveionsagainsttheirconcentrationgradientby
allowinganotheriontodiffusedownitsconcentrationgradient.
IonChannelsIonchannelsallowionstodiffusedowntheirconcentrationgradient,canbevoltage-gated,
canbeligand-gated,andcanbemechanically-gated.
Therestingmembranepotentialofaneuron isprimarilyaproductof theelectrochemical
gradientestablishedbythediffusionofpotassiumionsthroughpotassiumchannels.
Ionexchangers.
Theselectivityporeofanionchannelreplicatestherestinghydrationstateof
itsselectedion.
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PotassiumChannels
Kv, HERG, inward rectifier, calcium-activated, and two-pore potassium channels form
tetramers.
Kv,HERG,andinwardrectifierpotassiumchannelsarevoltage-gated.
Two-porepotassiumchannelscanbesensitivetoanaesthetics,lipids,heat,voltage,stretch,
andpH.
Inward rectifier and two-pore potassium channels contribute to the resting membrane
potentialofacell.
ThestructuresofKv,HERG,inwardrectifier,calcium-activated,andtwo-porepotassiumchannels.
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IonotropicReceptorsFastsynaptictransmissioninvolvesionotropicneurotransmitterreceptors.
FastExcitatorySynapticTransmission
IonotropicGlutamateReceptorsIonotropicglutamatereceptorsaretheprincipalfastexcitatoryneurotransmitterreceptors
of the central nervous system, are non-selective cation channels, and are tetramers of
subunitsthateachhavethreetransmembranehelicesandare-entrantloop.
AMPAglutamatereceptorsarepermeabletosodium,arepermeabletopotassium,andare
minimallypermeabletocalcium.
KainateglutamatereceptorsaresimilartoAMPAglutamatereceptors.
NMDA glutamate receptors are permeable to sodium, are permeable to potassium, are
permeable to calcium, have a glycine binding site, and are voltage-dependent due to a
magnesiumbindingsiteinthechannelporethatblockstheporewhenboundtomagnesium.
Therecyclingofglutamateatasynapse.
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NicotinicAcetylcholineReceptorsNicotinicacetylcholinereceptorsarefoundonskeletalmusclefibres,arenon-selectivecation
channels,andarepentamersofsubunitsthateachhavefourtransmembranehelices.
TheEPSCsproducedbytheopeningofAMPAandNMDAglutamatereceptors.
Therecyclingofacetylcholineatasynapse.
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FastInhibitorySynapticTransmissionFastinhibitorysynaptictransmissioninvolveschlorideionchannels,whichmaintainresting
membranepotentialbyshuntingEPSPs.
GABAAReceptorsGABAAreceptorsaretheprincipalfastinhibitoryneurotransmitterreceptorsofthebrain,are
pentamers,andarepermeabletochlorideions.
ThefunctionofGABAAreceptorsisaffectedbybenzodiazepines,barbiturates,steroids,and
picrotoxin.
TherecyclingofGABAatasynapse.
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GlycineReceptorsGlycinereceptorsaretheprincipal fast inhibitoryneurotransmitter receptorsof thespinal
cord,arepentamers,andarepermeabletochlorideions.
Therecyclingofglycineatasynapse.
GABAAreceptorsproduceEPSPsinimmatureneurons.