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 and how is it measured
- The potential difference (mV) between two electrodes placed inside and outside the cell.
2, A sharp electrode in the soma records the electrical potential across neuronal membrane - ~-70 mV in most neurones
4, Depends on separation of charge across lipid bilayer membrane - Charge resides on ions inside and outside cell
- Permeability of membrane is crucial
What is depolarisation?
- Increase in membrane potential.
2. The potential moving from RMP to less negative values
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 = RT/zF x log [ion]outside/[ion]inside.
- F = faradays constant
- z=charge on ion
- T=absolute temperature
- 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, 2. pumps against concentration gradient
- 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
- Vm= RT/F *(Pk[K+]out+ PNa[Na+]out+ PCl-[Cl-]in/Pk[K+]in+ PNa[Na+]in + PCl-[Cl-]out)
- Pion- relative permeability of membrane to ion
- [ion]out- concentration of ion outside the cell
- [ion]in- concentration of ion inside the cell
- F = faradays constant
- T=absolute temperature
- R=gas constant.
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
2. open and closed
Sequence for an 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