Trans - Neuronal Excitability I Flashcards
cytoskeletal fast transport uses
kinesin
cytoskeletal fast retrograde transport uses
dynein
special feature of axon hillock
large number of Na gates for start of impulse propagation
end of axon
terminal bouton
normal resting membrane potential
-70 mv at rest
resting membrane potential is mainly influenced by
- permeability of the membrane for each diffusible ion species
- cncentration of ions inside and outside the cell
3 mechanisms to generate RMP
- transmembrane K gradient through nongated leak channels
- Donnan effect.
- Na-K pump
main mechanism to generate RMP
transmembrane K gradient through nongated leak channels
Na-K pump contributes how much to RMP
20%
concentration gradient of K
high inside the cell - tends to move out
concentration gradient of Na
high outside the cell - tends to move in
concentration gradient of Cl
high outside the cell - tends to move in
Gibbs-Donnan equilibirum
in the presence of a nondiffusible ion, diffusible ions distribute themselves so that at equilibrium, their concentrations are equal
consequence of Gibbs-Donnan equilibrium
differential distribution of diffusible ions when a nondiffusible ion is present
Donnan effect
asymmetric distribution of permeant ions at equilibrium resulting in an electrical difference across the cell membrane
Donnan effect - to maintain electrical neutrality, there will always be a (1)______ K concentration inside the cell and a (2)_____Cl concentration outside
- greater
2. greater
side effect of donnan effect
accumulation of osmolytes in ICF - corrected by Na-K pump
Donnan effect - proteins within the cell limit diffusion of what ion down its concentration gradient
Cl
Donnan effect - what two forces are created in relation to movement of K
- force pulling K in –> due to electrical gradient
2. force pulling K out –> due to chemical gradient
force that moves solutes
diffusion pressure
Nernst equation - requirements
semipermeable membrane, diffusible species present, electrical and chemical gradient present
relationship of diffusion pressure and electrical pressure in equilibrium
equal
equilibrium potential of K
-90mv - tends to go out
equilibrium potential of Na
60mv - tends to move in
equilibrium potential of Cl
-70mv - does not move (diffusion pressure = electrical pressure)
what ion is really responsible for resting membrane potentials? why?
K, because it is freely diffusible at rest (K leak channels)
why is the equilibrium potential of K different from the RMP?
Na channels are not completely closed –> small influx of positive ions, bringing the potential up from -90 to -70
Goldman Constant Field Equation
takes into consideration all ions involved, used to calculate the true value of RMP
why can’t the Nernst equation be used to find the value of RMP
Nernst takes into account only one ion; there are many in this system
most flux of the 3 major ions
K (high permeability)
least flux of the 3 major ions
Cl (does not move)
[T/F] resting membrane potential is in absolute equilibrium
F
[T/F] resting membrane potential is constant
T
with lack of energy from ATP, what will happen to RMP? why?
it will dissipate because the ions are not in absolute equilibrium
which ions have almost no contribution to RMP according to the Goldman Equation
Na, Cl
action of Na-K pump
3 sodium out, 2 potassium in
function of Na-K pump
- prevent cell swelling
2. maintain RMP at -70mV
[T/F] energy is required to maintain the steady state equilibrium of RMP
T
