L4 Equilibrium Potential Flashcards
Electrical potential energy
Voltage difference across membrane
More charges you separate
The higher membrane potential energy
What’s the distribution of ions across the plasma membrane?
Slightly pos outside
Slightly neg inside
Ion channels
Polypedtide chain that forms water-filled pore
Are selective
3 general types of channels
Ungated/leaky channels
Ligand gated channels
Voltage gated channels
Ungated/leaky channels drive
Resting membrane potential
Ligand/chemical gated channels drive
Graded potentials
Voltage gated channels drive
Action potentials
Two driving forces for diffusion of ions through open channels
Chemical driving force (conc gradient)
Electrical driving force (separation of charges)
Electrochemical gradient
Chemical and electrical driving forces combined
Can act in same or opposite directions
How long will the net flux of an ion continue?
Once concentration and electrical gradient are equal and opposite AKA when it’s in electrochemical equilibrium
Equilibrium potential
Refers to diffusion potential (electrical force) that exactly balances or opposes the tendency for diffusion down an ions concentration gradient
Magnitude of potential is directly proportional to
Magnitude of concentration gradient
K+ equilibrium potential
K+ conc greater inside cell
Conc gradient moves K+ outside cell forming electrical gradient across membrane
Outside + , inside -
The electrical gradient then moves K+ back inside cell
No further movement when inward electrical gradient exactly counterbalances the outward conc gradient
-90mV
Na+ equilibrium potential
Na+ greater outside than inside
Conc gradient moves Na+ inside, creates electrical gradient that then moves Na+ back into cell
Once equal and opposite no further movement
+65mV
Nerst Equation
Gives equilibrium potential for one ion
E ion = (60/z) log ([ion]out /[ion]in)
Z= ionic valence or charge Na=+1, K=+1, Ca=+2, Cl=-1
[ion]out = extracellular conc for ion mM [ion]in = intracellular conc for ion mM
Log 10^x =
X
Only ions that move across the membrane contribute to
Equilibrium potential
If a membrane is permeable to both ions then there is
No separation of charge
You can only get a potential energy of membrane is
Permeable to something and
Impermeable to something else
Do organisms want to be at equilibrium?
No
Na+, K+, and Cl- ions are not in equilibrium
Organisms spend much of their energy establishing and maintaining various gradients
What’s the Ek+
-90mV
What’s the Na+ equilibrium potential ?
+65mV
Where is Na+ greater?
ECF 150mM/L
In ICF 15 mM/L
