Presentation on theme: "Neurotransmitter Release Signal Received (EPSP/IPSP)"— Presentation transcript:
1 Neurotransmitter Release Signal Received (EPSP/IPSP) What is an Action Potential?Break Down:Resting Membrane PotentialAP GenerationSignal PropagationNeurotransmitter ReleaseSignal Received (EPSP/IPSP)Repeat
2 The arrival of an action potential at the terminal will cause calcium, Ca+, to enter the cell and release vesicles filled with neurotransmitter.So, what will it do to the post-synaptic membrane? -change it’s potential, EPSP or IPSP
6 Receptor (ion channel) NeurotransmitterReceptor (ion channel)Neurotransmitter engages a receptor (lock-and-key)Receptor may be an ion channelIf it opens an ion channel…
7 Sodium ion flow inward is responsible for the generation of an EPSP. Would Na+ cause depolarization at -90? 0? +20? – yes, although -55 is threshold, after that Na+ is still depolarizing, as well as overwhelmingHow does this make the cell more likely to fire?Sodium ion flow inward is responsible for the generation of an EPSP.
8 IPSPWhy is it inhibitory? What does it do to the post-synaptic membrane? – lets in more neg ion into neg cell, and makes it more neg than before.Chloride ion flow inward is usually responsible for the generation of an IPSP
10 Multiple InputsPost-synaptic membrane may receive an excitatory post-synaptic potential (EPSP) and become depolarizedorPost-synaptic membrane may receive an inhibatory post-synaptic potential (IPSP) and become hyperpolarizedor BOTH Multiple excitatory and inhibitory inputs onto dendrites and the soma summate.
11 What about when you’re getting multiple signals of the same kind What about when you’re getting multiple signals of the same kind? When there are many neurons, what decides if another fires an AP?
12 EPSP summation is decrimental- it is proportional to input Spatial SummationAn action potential is not decrimental. Once threshold is crossed, the AP is always the same size and is not proportional to the input.So, is it a democracy? (Spacial…) or is it ruled by special interests and lobbyists (temporal)?EPSP summation is decrimental- it is proportional to inputTemporal Summation
14 SummaryNeurotransmitter released causes change in ion permeability on post-synaptic membrane.Depending on ion, causes an EPSP or IPSPEPSPs and IPSPs are summated spatially and temporally
15 Summary - Action Potential Initially the cell is resting at around -70 mV.Cell receives EPSPs and IPSPs from other neurons.The cell becomes excited (depolarized) enough…Threshold (-55 mV) is reached, voltage-gated Na+ channels open and action potential is sent down axon from the axon hillock.Inward rush of Na+ depolarizes adjacent area of axon and preps new AP site.The AP peaks (+35 mV), Na+ channels close and voltage-activated K+ channels open.K+ efflux follows Na+ influx down the axon and causes hyperpolarization that prevents the AP from traveling backwards.AP reaches axon terminal. Ca+ enters and releases vesicles filled with neurotransmitter.NT crosses the synapse and binds receptor on post-synaptic cell
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18 What is a membrane potential? -difference in voltage across the membraneWhat is the value of the RMP of a neuron?-it’s -70mVWhat inside the cell is large, immobile, and negative?-proteins, A-What does selective permeability mean?
19 is different from positive ion and negative ion . is negative. Which way is concentration force of ?Which way is electrical force of ?
20 Cl- Outside IN OUT K+ Inside Na+ Define the Chemical and Electrical forces on these ions in a neuron at RMP (-70inside)More concentrated on the…Concentration gradient pushes it…Electrical gradient pushes it…Cl-OutsideINOUTK+InsideNa+
21 Determine Chemical and Electrical forces on K+ at different membrane potentials (*remember it’s still highly concentrated on the inside)Chemical force pushes it…Electrical force pushes it…At RMP (-70 mV)OUTINAt peak (+35 mV)
22 Depolarize or Hyperpolarize? Membrane potential travels from -70 → -55DepolarizeMembrane potential travels from -70 → 10Membrane potential changes from -70 → -80HyperpolarizeNa+ enters cell DepolarizeNegative Cl- enters resting cell (-70) Hyperpolarize
23 EPSPs (generator potential) What Phase?EPSPs (generator potential)Return to RMPRapid DepolarizationRMPRepolarizationThresholdHyperpolarizationAt this point, not looking for info about channels, just basically, is it depol, hyper, threshold, etc.
24 Na+/K+ pump working (Na+ out and K+ in) non-v-gated and v-gated Na+ IN What channels are open? Which ions are moving? Which direction?Na+/K+ pump working (Na+ out and K+ in)non-v-gated and v-gated Na+ INK+ leak ↨Na+ INK+ OUTK+ OUTAt this point, not looking for info about channels, just basically, is it depol, hyper, threshold, etc.
25 The permeability (leaking) of which ion is proportional to the RMP Which ion enters the cell, depolarizes the membrane and starts the APNa+Which ion repolarizes the membrane by leaving the cellHyperpolarization is the function of which ion channels remaining openWhat channel/pump maintains and reestablishes the RMP?Na+/K+ pump
26 K+ leaks out across the membrane more easily than Na+ leaks in The Na+/K+ pump trades 3 Na+ for 2 K+, does this really restore balance?Yes, because the neuron does not stay at RMP for long, it will fire APs, and eventhough there is an efflux of K+ from the neuron, there is so much Na+ influx that a 3:2 by the pump restores the correct balance.
27 True or FalseIon distribution at resting in the axon is like that of the dendrites and soma TRUEElectrical and chemical gradients act differently on ions in the axon than in the soma FALSEK+ efflux follows Na+ influx as it proceeds down the axon. TRUENa+ starts entering the next site while K+ is hyperpolarizing the old site. TRUE
28 Myelination pushes the field of depolarization from Na+ entry further than it would go in an unmyelinated axon. TRUEIn saltatory conduction, the depolarization jumps over the outside of the myelin. FALSENa+ is already depolarizing the next node while K+ is beginning to efflux. TRUEAn AP starts out at full force and gets weaker as it travels down the axon. FALSE
29 Depolarization from Na+ is not localized, but also effects nearby membrane. What does it do there? What is the importance?Depolarizes neighboring membrane to threshold so that it opens v-gated Na+ channels and fires AP next.If you put an electrode into the middle of an axon and stimulate (depolarized it), the AP would go in what direction? Why? Both. There wouldn’t be any hyperpolarization from K+ efflux following it until after the AP is started by the electrode.The hyperpolarization will follow it in both directions.
30 An AP is sent from the axon hillock. Entry of which ion besides Na+ is important for release of vesicles containing neurotransmitter?Calcium, Ca+Name two ways in which EPSPs and IPSPs summateTemporal and spatialIf there are enough EPSPs, what happens?An AP is sent from the axon hillock.
31 EPSP or IPSP? GABA receptor lets Cl- into cell IPSP Ach receptor lets Na+ into the cell EPSPAch receptor lets Ca+ into the cell EPSPGlycine receptor lets Cl- into the cell IPSPA different GABA receptor causes K+ to leave the cell IPSP
32 Be able to…Determine which direction K+, Na+, and Cl- would travel at various membrane potentials (ex. -70, -55, 0, 30)Describe which ions are moving and why at each stage of the APPredict change in AP profile under influence of neurotoxins (Ex. TTX that blocks v-gated Na+, a toxin that blocks K+ efflux)Predict the effect of a neurotransmitter on the post-synaptic membrane, ie EPSP or IPSP (Ex. Ach → NA+ influx and GABA →Cl- influx)
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