Kims objectives Flashcards
how is membrane potential established
Vm based on charge imbalance driving for and permeabililty basically just ions being uneven ground is outisde cell
Equilibrium potential, Ex
nernst potential so based on concentration and charge
K is like -95
Na is like 35
Cl is near -Vm
Driving force
DF=Vm-Ex VmEx outward (DF>0) Vm=Ex no net
voltage clamp
decide the voltage
record current needed to maintain
squid axon example
current clamp
decide the current, measure the voltage
action potential generation
EPSP have AMPA receptor that opens to letting Na in to depolarize
IPSP have GABA receptor letting in Cl to hyperpolarize
rising, falling, undershoot
voltage gated channels
K has 4 subunits and one gate, slow to activate and deactivat, opens with depolatiation just slowlly
Na has alpha and beta subunits, two gates, one opens opens at threshold and then the other closes after 1ms and stays closed until repolarization
currents underlying action potential phases
rising phase is inward current of Na
falling phase and undershoot - K outward current
refractroy periods
make it unidirectional because of Na inactivation
conductance
flow of ions through channels
conductance
flow of ions through channels
g in R=1/g
capacitor
stores charge
analogous to neuronal membrane
negative inner, positive outter
capacitor
stores charge
analogous to neuronal membrane
negative inner, positive outter
What happens when depollarized Vm=-40
Force on Na decreases because it closer
Force on K increases because further
force on Cl increases
outward current inward Cl
current
flow of positive charge so direction of Na and opposite of Cl
hyperpolarized to -90
Force on Na increases because further
no net force on K because nearer
force on Cl reverses
inward current outward cl
Permeabliity
determines resting membrane potetnial
basically if youre more permeable then Vm is closer to Ex
K>Na»Cl so Vm is near K but not K because of Na
so flux of Na and K aer equal and opposite at rest
what determines resting potential
GHK
Concentration and permeability of Na and K
what factores determin net movement
driving force and permeablity
DF=Vm-Ex
what influences driving force
concentration
electrostatic force
membrane potential
patch clamps
by either just grabbing or pinching off sections you can measure current from different directions
time constatn
Tau=RC
time it takes to get to 63% of ss value
big C so slow build up
Big R large charge requiered to change
cable theory
larger diameter and more myelination makes more efficient conductor
TTX
blocks Na channels
so no depolarization
