Student questions of the dayStudent questions of the day……..Q: Can’t an initial depolarization traveldown the length of the axon? A: No, the ions entering the cell diffuse awayA: No, the ions entering the cell diffuse awayfrom the depolarization site, which then needs to be from the depolarization site, which then needs to be regenerated.regenerated.Q: How does reaching threshold potential lead to massive opening of voltage-gated Na+ channels?A: At threshold potential, there is a conformational A: At threshold potential, there is a conformational change in the channels, so they open fully. change in the channels, so they open fully. 7.0134.20.07Systems INervous system 2Creteko and BehringerNervous system in developing bat: neurons stained for neurofilament protein1Chemical synapse Pre-synapticterminalPost-synaptic terminalSee Purves 44.132axondendrite+Outside cellInside cell++++++++-+++++++++++++++++++++++++CHANNELS THATGENERATE RESTING POTENTIAL++++++HIGH Na+LOW K+LOW Na+HIGH K+3Na+ pumped out2K+ pumped inNa/K ATPase++H. Sive MIT 2007+3+++openK+ channel K+ - outward diffusion- inward electric forceOutside cellInside cell+++++++++++++++++++++++++++++++++++CHANNELSTHAT GENERATE ACTION POTENTIAL++++H. Sive MIT 2007Na+ involtage-gated Na+channelsopen4++Threshold potential causes….Outside cellInside cell+++++++++++++++++CHANNELS THATREPOLARIZE+++H. Sive MIT 2007++++++++ +K+ outvoltage-gated K+channelsopen+5+++open K+, Na+, Cl- channelsNa/K ATPaseNa+ out Cl- in----------+After an action potential…..Outside cellInside cell+++++++++++++++++++++++++++++++++++CHANNELSACTIVATED ON PRE-SYNAPTIC MEMBRANE++++H. Sive MIT 2007Ca2+ involtage-gated Ca2+channelsopen6++Action potential (Na+ influx) in axon leads to…Neuron (cell body and dendrites) with each synapse shown as a dot7Increase in synaptic density in early childhood8Excitatory vs inhibitory synapsesPurves 44.15: post-synaptic membrane sums inputover time and space >> action potential9/inhibitoryOutside cell:synaptic cleftPostsynapticcell H. Sive MIT 2007Excitatory synapses:CHANNELS THAT HYPOPOLARIZE: increase resting potential closer to threshold potentialResting potential-55mVThreshold potl-50mVGated Ca2+channels openGated Na+channels openhigh Na+, low K+, high Ca2+, high Cl-low Na+, high K+, low Ca2+, low Cl-10Normal resting potential = 60mVOutside cell:synaptic cleftPostsynapticcell Inhibitory synapses:CHANNELS THAT HYPERPOLARIZE: decrease resting potential away from threshold potentialResting potential-65mVGated outward K+channels openThreshold potl-50mVGated Cl-channels openH. Sive MIT 2007high Na+, low K+, high Ca2+, high Cl-low Na+, high K+, low Ca2+, low Cl-11Normal resting potential = 60mVAcetylcholinecan be an excitatoryor inhibitoryneurotransmitter12Summationspatial temporalPurves 44.15: synaptic summation13Neuronal firing:modulation of frequency, notamplitude14NeurotransmittersNeurotransmitters (see Purves Table 44.1)15ReceptorsPurves 44.14: acetylcholine (Ach) receptor is ionotropic (= ion channel) (nicotinic)16Purves 44.16: metabotropic receptors activate ion channels indirectlyAch can also be metabotropic (muscarinic)17Controlling neurotransmitteractivityAcetylcholineneurotransmitterAtropineinhibits acetylcholine receptor(antidote to nerve agent)18Acetylcholine/receptor binding and degradation by acetylcholinesterase19Inhibition of acetylcholine degradationby nerve agent20Inhibition of acetylcholine/receptor bindingby atropine21Serotonin= neurotransmitterProzacSpecific serotoninre-uptake inhibitor(SSRI)MDMA= ecstacy3,4-METHYLENEDIOXY-N-METHYLAMPHETAMINECauses massive serotonin release22Normal serotonin reuptakeWithserotonin reuptake Inhibitor PresynapticneuronPostsynapticneuron23Adenosine brain function sleepyCaffeinecompetitive inhibitor
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