Exam 2: Ch 5 Notes Flashcards
what is a neuron
specialized cell that communicates via electrical activity
how does the nervous system work
input –> dendrite –> soma processing –> output –> synapse
is shape (morphology) important
yes
can inputs be excitatory or inhibitory?
yes
graded potential
vary in size
generated by inputs
action potential
invariant in size in a particular neuron
all or none
what do glia do and how many are there
support neuronal function
10x more than neurons
functions of glia
regulate extracellular ion concentrations, regulate neurotransmitter concentration
buffer reactive oxygen species
metabolic support, insulation
astrocytes
glia that are more numerous in the brain
fills paces between neurons
influence neurite growth, survival, and function
resting potential
inside the cell its negative -45mV to –80mV
maintained at all times by concentration gradient of K through leak channels
passive membrane properties
resistance
capacitance
what is gating
a stimulus that opens the gate (channel etc)
voltage or transmitter gated
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
resistance is related to …
channels
capacitance is related to
insulating nonpolar lipid tails and conducting polar lipid heads
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
2 driving forces of resting potential
[ ] gradient
electrical driving force
what is equilibrium potential
[ ] driving force is equal and opposite to the electrical driving force
no net movement of charge
at resting potential what channels are not open in a neuron
voltage-gated
NT-gated
at resting potential what channels are open in a neuron
mostly K+ leak (flows out due to [ ] gradient, mostly neg resting pot)
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
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
what is the nernst equation used for
calculate exact value of equilibrium potential for a single ion in mV
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
