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psy383_Action_Potential

If you want to understand drugs, you have to understand the action potential.
by

Will Moore

on 10 February 2013

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Transcript of psy383_Action_Potential

ion EPSP ion voltage gated ligand gated permeability depends on membrane potential permeability depends on presence of drug/NT allow ions to cross the cell membrane (permeability) excitatory -70 mV +55 mV passive permeability depends on structure of the pore -45 mV inhibitory IPSP 1. 2. 3. 5. 6. 0 mV 4. positive
feedback
loop Na channels are more likely to open
when the membrane is depolarized when Na channels open, the
membrane gets depolarized probability action potential probability action potential INCREASE DECREASE summation charged atom
(or molecule) Na K Ca Cl equilibrium at resting potential
(passive channels)

restores resting potential through efflux (voltage gated chanels)

Na/K pump maintains equilibrium equilibrium at peak
(voltage-gated channels)

influx causes depolarization (voltage-gated channels) influx causes depolarization
(voltage-gated channels)

acts as 2nd messenger

causes vesicles to fuse w/ presynaptic membrane Cl hyperpolarizes cell (inhibitiory effect)

voltage-gated & ligand gated ion channels Cl hyperpolarizes cell (inhibitiory effect)

voltage-gated & ligand gated ion channels passive K channel K gated voltage Na Na -70 mV Na gated voltage Na Na K equilibrium at resting potential
(passive channels)

restores resting potential through efflux (voltage gated chanels)

pump maintains equilibrium gated voltage K K Ca gated voltage +30 mV Ca Ca Ca Cl voltage gated Cl Na K Ca Cl equilibrium at resting potential
(passive channels)

restores resting potential through efflux (voltage gated chanels)

pump maintains equilibrium equilibrium at peak
(voltage-gated channels)

influx causes depolarization (voltage-gated chanels) influx causes depolarization
(voltage-gated channels)

acts as 2nd messenger

causes vesicles to fuse w/ presynaptic membrane hyperpolarizes cell (inhibitiory effect)

voltage-gated & ligand gated ion channels K -70 mV K K Na Na Ca Ca Cl Cl 1. 2. 3. 4. 5. 6. Action Potential channels Resting Potential Action! Na +30 mV K K When voltage-gated calcium channels open... $#@& gets crazy!!! Na Na 1. 2. Na gated voltage Na Na Na K Ca Cl equilibrium at resting potential
(passive channels)

restores resting potential through efflux (voltage gated chanels)

pump maintains equilibrium equilibrium at peak
(voltage-gated channels)

influx causes depolarization (voltage-gated chanels) influx causes depolarization
(voltage-gated channels)

acts as 2nd messenger

causes vesicles to fuse w/ presynaptic membrane hyperpolarizes cell (inhibitiory effect)

voltage-gated & ligand gated ion channels K -70 mV K K Na Na Ca Ca Cl Cl Resting Potential Na What if you administer a drug that
blocks voltage gated Na channels? -70 mV +55 mV -45 mV 0 mV +30 mV because TTX blocks the channel usually, voltage determines permeability... but now, change in voltage doesn't matter Tetrodotoxin ( TTX ) ~ 10 x more poisonous than potassium cyanide

LD50: 334 ug / kg (oral) ; 8 ug/kg (IV)

used in Vodou to create zombies? ug = millionth of a gram in mice 豚 fugu posion puffer fish liver, ovaries, skin contain high concentrations of TTX

license requires 2-3 years of training

praised for umami flavor Wait, toxin? That doesn't sound like a drug.
Who would willfully ingest poison? also associated with tingling sensation or numbness of mouth and tongue

less often discussed: euphoric / psychedelic effects of fugu experience

expectaion effects? TTX: voltage-gated sodium channel blocker bare necessities: neurons are negatively charged at rest (polarized) -70 mV +55 mV -45 mV 1. 2. 3. 5. 0 mV 4. +30 mV What if a drug blocks potassium channels? chlorine influx still allows repolarization, but it's sloooowwww How else might you achieve this effect? What are the downstream consequences? this is clutch for serotonergic activity Clarivius Narcisse pronounced dead in 1962

returned to home village in Haiti in 1980

claimed to have been turned into a zombie slave Wade Davis Harvard ethnobotanist

cold busted for robbing a kid's grave

claimed to have discovered recipe for... Datura stramonium wide variety of substances secreted by genus bufo ('true toads') tetrodotoxin deleriant containing
bella donna alkaloids bufotoxins zombie powder Would TTX induce mindless, slave-like, zombie behavior? the RECEPTOR does! even though GABA is the primary inhibitory neurotransmitter, the transmitter itself doesn't really matter... + + potassium efflux restores the resting potential (along with metabolic pumps) when the cell becomes positively polarized, calcium can enter at the axon terminals, leading to NT release if a neuron becomes depolarized to threshold (-45mV), positive feedback from sodium influx causes a 'spike' * * Calcium causes vesicles to fuse to the presynaptic membrane,
releasing NT into the synapse structure determines function gates which can be open or closed
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