Resting Membrane Potential Flashcards
What does membrane potential do?
Provides the bass of signalling in the nervous system as well as other cell types
How do we measure membrane potential?
Use a micro electrode (fine glass pipette)
It is full of conducting solution (KCl)
Voltage outside cell = 0
Electrode penetrates membrane and measures cell voltage inside cell (always -ve)
Define membrane potential. What is the unit of measurement for membrane potential?
The electrical charge hat exists across a membrane and is always expressed as the potential inside the cell relative to the extracellular solution.
Measured in mV
What is the resting potential of cardiac myocytes?
-80mV
What is the eating potential of neurones?
-70mV
What is the eating potential of skeletal muscle myocytes?
-90mV
What is the resting potential of smooth muscle myocytes?
-50mV
What are some properties of ion channels?
1) selectivity for one (or few) ion species
2) gating, pore can open/close by conformational change in the protien
3) rapid ion flow, always down electrochemical gradient
Hw do cells set up resting potential?
Open K+ channels dominate the membrane at rest.
The chemical gradient wants K+ out, the electro gradient wants it in.
When these gradients are equal and opposite, there is no movement of K+ but there is a -ve membrane potential.
Therefore, resting potential Arises because membrane is selectively permeable to K+.
What is the Nernst Equation for?
Finding the equilibrium potential of an ion.
Can rearrange to RT/zF times Log10 of ((K+ outide)/(K+ inside))
Why in a real cell is resting potential not the same as K+’s equilibruim potential?
As real cells are leaky.
The K+ channel is voltage insensitive so always open.
But Na+/Ca+ are voltage gated, so occasionally spontaneously open for small amount of time causing leaking that depolarises the cell.
Cl- is also leaky so causes slight polarising of the cell
Why is the cardiac muscle and nerve cells rest Potentials at -80mV and -70mVs?
Both resting potentials quite close to E(K+).
However, not exactly as E(K+) as the membrane isn’t perfectly selective for K+. (Leaky)
Why do some cells have low resting potentials? (Eg smooth muscle at 50mV)
They have a lower selectivity for K+, so there’s increased contribution from other channels
Why does skeletal muscle have a resting potential of -90mV?
As Thereare many open Cl- and K+ channels open.
So resting potential is close to both E(Cl-) and E(K+)
