Exam 2: Ch 5 Notes Flashcards by Molly Gallagher

what is a neuron

specialized cell that communicates via electrical activity

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how does the nervous system work

input –> dendrite –> soma processing –> output –> synapse

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is shape (morphology) important

yes

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can inputs be excitatory or inhibitory?

yes

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graded potential

vary in size

generated by inputs

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action potential

invariant in size in a particular neuron

all or none

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what do glia do and how many are there

support neuronal function

10x more than neurons

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functions of glia

regulate extracellular ion concentrations, regulate neurotransmitter concentration

buffer reactive oxygen species

metabolic support, insulation

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astrocytes

glia that are more numerous in the brain

fills paces between neurons

influence neurite growth, survival, and function

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resting potential

inside the cell its negative -45mV to –80mV

maintained at all times by concentration gradient of K through leak channels

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passive membrane properties

resistance

capacitance

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what is gating

a stimulus that opens the gate (channel etc)

voltage or transmitter gated

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what is responsible for passive/active electrical membrane properties

channels w/ gating and selectivity

leak channels open at rest (K+)

voltage-gated Na, K, Ca channels move ions down [ ] gradient

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resistance is related to …

channels

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capacitance is related to

insulating nonpolar lipid tails and conducting polar lipid heads

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how do resistance and capacitance work

when voltage is applied, current goes to the capacitor b/c there is no resistance

resistance inc as charge builds, and current goes to a resistor

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2 driving forces of resting potential

[ ] gradient

electrical driving force

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what is equilibrium potential

[ ] driving force is equal and opposite to the electrical driving force

no net movement of charge

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at resting potential what channels are not open in a neuron

voltage-gated

NT-gated

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at resting potential what channels are open in a neuron

mostly K+ leak (flows out due to [ ] gradient, mostly neg resting pot)

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at resting pot is the [ ] gradient changed by K+ leak channels?

no, only takes a few diffusing K+ ions to set up inside neg resting pot

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what is essential to maintaining [ ] gradient of Na+ high out and K+ high in

Na/K ATPase of 3 Na out/2 K in per 1 ATP

Na leaks in so must be pumped out to keep [Na] in cell low

ouabain tipped arrow can kill a hippo

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what is the nernst equation used for

calculate exact value of equilibrium potential for a single ion in mV

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what does nernst equation depend on

temp (K)

charge of ion (pos or neg)

[ ]s of each ion of either side of the membrane

nernst equation formula

Ek = (RT/zF) ln ( [ion out] / [ion in] ) Ek = voltage z = charge of ion

in squid giant axon Ek+ = -93 mV and ENa = 56 mV... which one "wins"?

depends on permeability of membrane to each ion cell resting pot is ~ -70 mV so K+ contributes more than Na+ this is due to large K+ conductance and small Na+ conductance (many K+ leaks channels and only a few Na+ leak channels)

nernst potential indicates which ions are involved in...

resting potential membrane potential

action potentials change the ______ of the membrane

permeability

what is the Goldman equation used for

calculate the voltage contributions of multiple ion species to equilibrium potential

what does goldman equation depend on

[ ] gradient of each ion permeability (P) of the membrane to each ion

3 things to maintain resting potential

[ ] gradients mechanism to maintain gradients (Na/K ATPase) selective permeability`

if theres a smaller [ ] gradient then there is a _____ driving force and less _____ resting potenetial

smaller, negative

permeability of K and Na at rest

K high Na low

electrical driving force on ion equation

E = Vm - E(ion) ex. if cell is at -70 mV and ENa = 62 then E = 132 mV

6 properties of an action potential

all or none same size all the time (1 exception) regenerative above threshold (pos reinforcement loop) go above 0 mV post-AP hyperpolarization refractory period

when an input depolarizes a cell what happens in general

voltage-gated Na channels open (changes conductance) and the voltage changes if input depolarizes above threshold you get an AP if input does not reach threshold there is no AP

what is the positive feedback loop of reaching threshold

depol --> open voltage-gated Na channels --> Na in --> depol

which voltage-gated channels are faster to open

Na+ conductance is rapid K+ conductance has a slower onset (slower to open) due to chem. properties

what is AP shape dictated by

channel properties Na looks normal Ca looks like a plateau

at rest, leak channels maintain...

rising phase: voltage gated Na falling phase: voltage gated K

full cycle of depol

input --> open voltage gated Na and Na moves in ---1 ms---> voltage-gated Na channels inactivated and no Na moves ---back to -----> -60mV due to K+ channels -----> Na channels close and cell ready to be depol again

what causes voltage-gated Na channel inactivation

absolute refractory period during AP

inward current makes a _______ inflection

downward

outward current makes an _______ inflection

upward

what does measuring AP current look like

initial inward current from Na ions later outward current from K ions

if sustained stimulus

rapidly adapting ---> only fires at change slowly adapting ---> continuous fiing

fugu sushi (pufferfish)

tetrodotoxin TTX blocks voltage-gated Na channels blue ringed octopus california newt

lidocaine blocks...

Na channels (dentists)

what if double stimulus

2nd AP smaller than the 1st if the stimulus is during the relative refractory period K channels still open not all Na channels have closed, still some inactivated

squid giant axon (giant diameter) voltage clamping hypothesis

Na+ drives depol to cause AP made artificial seawater w/o Na+

squid giant axon voltage clamping experiment results

rising phase of AP driven by inward Na current falling phase of AP driven by outward K+ current Na open fast K open with lag/delay

squid giant axon voltage clamping experiment

stimulation electrode passes current to hold cell at 60 mV ---> channels open ---> current flows ----> voltage clamp measures current ---> plays same current back to cell

voltage gated ion channels respond to ________

depol

are Na channels ion specific?

yes voltage sensor activation gate ball + chain mechanism

ion specificity

dimensions charge at mouth selectivity filter lining the channel ions lose H2O of dehydration and interact w/ charges inside channel

Patch clamping

voltage clamp a patch of membrane single channel neurons and channels

problem with patch clamping neurons

multiple types express protein in an artificial bilayer or cell w/o channel (frog oocyte)

K channel structure

each gene codes for a subunit (4)

na channel structure

all 4 subunits are the same and coded for by the same gene