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Lecture 06, 11 Sept 2003Chapters 6 and 7Vertebrate PhysiologyECOL 437University of ArizonaFall 2003instr: Kevin Boninet.a.: Bret PaschVertebrate Physiology 4371. Nervous System (CH6, CH7)5-2 Randall et al. 2002Chapter 6 (con’t)Neuronal Communication- neurons- support cells- neuronal circuits- synapses6-1 Randall et al. 2002Action Potentials-Accommodation5-19 Randall et al. 2002Silverthorn 2001. 2nd ed. Human Physiology. Prentice HallGLIAL:-Schwann cells in peripheral nerves-Oligodendrocytes in CNSNodes of Ranvier and Saltatory Conduction6-7 Randall et al. 2002 (Electrotonic vs. Regenerative)Silverthorn 2001. 2nd ed. Human Physiology. Prentice Halllongitudinal currentvs. cross membrane#3 on Bret’s lab handoutWill transmembrane current at C (when AP at B)be greater, less, or the same compared totransmembrane current at B when AP at A??A B C D EAPmyelinateddemyelinatedNode of RanvierMultiple sclerosis caused by demyelinationRandall et al. 2002A given nervebundle can havemultiple axons,each withdifferentconductionvelocities.6-8 Randall et al. 2002p. 214, Silverthorn2001. 2nd ed.Human Physiology.Prentice HallSynapsesChemical1- fast (direct)2- slow (indirect; 2nd messenger)Ligand-gated ion channels(psp); NT from active zoneBiogenic amines orneuropeptidessynaptic cleftsynaptic vesiclesRole of Ca2+6-11 Randall et al. 2002SYNAPSES-communication between neurons or between neuron and effector organ1-electrical (rapid)2-chemical(‘fast’ or slow)1. De- or hyper-polarize2. Change # ion channels in membrane3. Alter rate of ion channel activity4. Modify sensitivity to activation signalsIn postsynaptic neuron:6-22 Randall et al. 2002Electrical Synapse (rapid) - direct ionic coupling via gap junctions-examples in retina, CNS, smooth muscle, cardiacmuscle, etc.gap junctions6-22 Randall et al. 20026-9 Randall et al. 2002SynapsesChemical Example1- fast (direct)Neuromuscular Junctions(Motor Endplates)Thousands of VesiclesAcetylcholine (ACh)AcetylcholinesteraseLots of usefulpharmacological agentsfor study ofneurophysiology (p.173)6-11 Randall et al. 20026-12 Randall et al. 2002SynapsesChemical Example1- fast (direct)Neuromuscular Junctions(Motor Endplates)Postsynaptic current (psc)Alter Membrane PotentialK+ and Na+ through sameACh activated channelpsc shorter than psp(b/c time constant)6-12 Randall et al. 2002Released by presynaptic neuron and causes postsynapticresponse (EPSP or IPSP) by altering ion channelpermeabilityNeurotransmittersLots of NTs conserved throughout animal kingdom1. Fast and direct (~ligand-gated channel)ACh, Glutamate, Aspartate, ATP2. Slow and indirect (biochemical pathways) Norepi, GABA, glycineKnow an example or two of eachNeurotransmitters1. Fast and direct2. Slow and indirectIncluding several neuropeptides act as NTsbut are also hormones etc.Presynaptic neuron may releaseboth a fast and a slow NTThese neuropeptides often synthesized insoma and transported down axon to site ofreleaseAgonist (mimics) vs.Antagonist (blocks) (-curare blocks ACh reception)Acetylcholine6-31 Randall et al. 2002AcetylcholinesteraseCholinergicNorepinephrine6-31 Randall et al. 2002AdrenergicPostsynaptic Neurotransmitter Effects1. Fast and direct2. Slow and indirecte.g., ACh receptors1 Nicotinic(muscles, autonomic/sympathetic NS)2. Muscarinic (parasympathetic, indirect)NT role depends primarily on receptorcharacteristics on postsynaptic neuronPostsynaptic Neurotransmitter Effectse.g., fast nicotinic ACh receptors1. Fast and direct6-32 Randall et al. 20026-34 Randall et al. 2002Postsynaptic Neurotransmitter Effects2. Slow and indirect e.g., G-protein mediated cascade6-36 Randall et al. 2002Silverthorn 2001.2nd ed. HumanPhysiology.Prentice HallSlowFastPostsynapticNeurotransmitterEffectse.g., indirectmuscarinic AChreceptors actingto reduce heartcell excitability6-37 Randall et al. 2002Integration at SynapsesThousands ofPresynaptic NeuronsSummation- Spatial- Temporal> 1 neuron 1 neuron 6-42 Randall et al. 2002Integration at SynapsesTemporal summation6-44 Randall et al. 20026-45 Randall et al. 2002Integration at SynapsesDecay of potentialsLocation of Synapse(e.g., IPSP with veto power)Thousands ofPresynaptic NeuronsSpatialSummation/IntegrationIPSPEPSP6-43 Randall et al. 2002EPSP and IPSPExcitatory orInhibitoryPostsynapticPotentialsNa+Ca2+K+Cl-EPSPIPSPpscpscpspGraded currentcausing gradedpotential:6-19 Randall et al. 2002Reversal PotentialOpening channel for a given ion species Xmeans Vm will move toward ExErev is the reversal potentialUse Nernst to calculate for one ion speciesGoldman equation for multiple ionsCan’t change membrane potential beyondErev for a given ion(s) and its channelsACh opens for K+ and Na+, so Erev between EK and ENaAltering Excitability or Synaptic


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UA ECOL 437 - Nervous System

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