9) Resting Potential Flashcards
Resting potential
This is when the electrical potential differs between the interior and exterior.
Usually from -50 - -100 mV
Measurement of resting potential
A glass microelectrode is inserted into cytoplasm
A second microelectrode is placed in the surrounding fluid
Potential different is amplified and measured
As resting potential the potential difference is 0
Bernstein hypothesis
The cell membrane is permeable to potassium ions
The resting potential is the equilibrium potential for the potassium ion
Nernst equation
⚠️🔱= 🔱I-🔱e
= KT/e ln cke/cki
Grounds for Bernstein’s hypothesis
The concentration is higher inside the cell than outside the cell
So it moves potassium out of cell
The inside will have a negative charge so electric field moves potassium into the cell
Equilibrium is possible
Equilibrium conditions
The resting membrane is permeable to potassium ions only
Or
All other ions are also in equilibrium
Discrepancy between Bernstein hypothesis and experiment
The potassium hypothesis is incomplete the membrane is permeable to other types aswell
Distribution of sodium ions
The cell membrane at rest is slightly permeable to sodium ions
The sodium ions are not in equilibrium
Both the electric and concentration gradients move them into the cell
The Hodgkin Katz theory
The resting potential is the potential of a steady state, not of an equilibrium state
The resting potential is the net result of the fluxes of potassium,sodium, chloride.
Charge flux across a membrane
The charge flux across the membrane is due mainly to the monovalent potassium sodium and chlorine ions
J= jk+kna-jcl
Steady state flux
J = jk + jna - Jcl = 0
The ion flux changes the membrane potential
The conditions for a steady state
Jcl = 0
Jk+jna = 0
The cl close to rest is at equilibrium
Driving forces for potassium and sodium
The conc and electrical potential gradient moves potassium ions in opposite directions
The conc and electrical potential tail gradient moves sodium in the same direction
Xk«_space;Xna
Membrane permeability for potassium and sodium
Some potassium channels in the resting membrane is open
All the sodium channels are closed
-permeability to sodium is very small
Pk» Pna
The potassium and sodium fluxes for steady state
Pkxk= PnaXna
It is possible for the potassium and sodium fluxes to be equal and opposite to each other
