Nerve cells and excitability Flashcards
How does the concentration of potassium ions vary inside and outside the cell?
K+ is high inside the cell but low outside the cell.
How can sodium or potassium be transported across the membrane?
Using sodium-potassium ATPase transporters that use ATP to transport the ions against the concentration gradient.
What is the resting membrane potential?
The potential difference (mV) between two electrodes placed inside and outside the cell.
What is depolarisation?
Increase in membrane potential.
Hyperpolarisation?
Decrease in membrane potential (more negative).
Where are pyramidal neurones found?
The hippocampus.
Where are Purkinje neurones found?
The cerebellum.
What does the Nernst equation allow?
The equilibrium potential for any ion to be calculated.
What is the Nernst equation?
Eion = 2.30RT/zF x log [ion]outside/[ion]inside. where F = faradays constant, z=charge on ion, T=absolute temperature and R=gas constant.
What is the refractory period?
When Na+ channels become inactivated as the membrane depolarizes and cannot be activated again until the membrane is repolarized.
What are graded (local) potentials?
Changes in the membrane potential that are confined to a small region of the membrane.
Distribution of charged ions
sodium potassium atp transporter maintains gradient, pumps against concentration gradient
3 Na+ out, 2 K+ in
using active transport
3 transporters
active transporters
ion channels- selectively permeable, ions diffuse down concentration gradient
voltage gated channels: passive, selective, rapid
what drives conformational change of channels
phosphorylation
How can Vm (RMP) be calculated
Goldman equation
repolarisation
potential moving back to RMP
propagation
movement of AP along axon
How many states do Na+ VGC’s exist in
3
open, closed, inactivated
once inactivated can’t go back to being open, have to go back to being closed, then open
how many states for K+ VGC
2
open and closed
Sequence for and action potential ( Na+ VGC’s)
Na+ open rapidly with depolarisation- influx of Na+ ions. Inactivation gate rapidly blocks Na+ permeability during continued depolarisation
Inactivated gates move to closed on repolarisation
Sequence for and action potential ( K+ VGC’s)
open slowly on depolarisation, K+ move out of cell, drawing +ve charge out
close slowly on repolarisation
K+ continue to move out till reach equilibrium potential for K+. no net movement
At this point K+ VGC closed and Na+ inactivated
Then pump establishes concentration gradient from the beginning
Threshold
point at which AP is generated
determined by extent of depolarisation
refractory period- why is it absolute?
because Na+ VGC are inactivated, unable to be opened (unlike in a close state) so cannot generate another membrane because it would require the membrane potential to be at rest and Na+ VGC’s to be open
refractory period- why is it relative?
because the membrane is hyperpolarised until K+ channels close, so an AP can only be generated if stimulus is stronger than usual