Resting Membrane Potential Flashcards
Membrane Potential
-All living cells have a plasma membrane potential (millivolts, mV)
-Separation of opposite charges across plasma membrane allows a potential to do work
-The membrane potential is due to differences in concentration and permeability of key ions (inside: neg; outside: pos)
Magnitude of Membrane Potential
Dependent on the number of opposite charges separated. The greater number of charges, the greater the potential
Ion Channels
-Polypeptide chains that form water-filled pores
-Channels are selective
-Some are open in the absence of stimuli (“leak” channels)
-Some have gates that respond to specific stimulus
-Multiple channels for a single ion
Diffusion of Ions through an Open Channel
-Chemical driving force: the concentration gradient
-Electrical driving force: separation of charges causes an electrical gradient
-Combined = electrochemical gradient
-Forces can act in the same of opposite directions
-Diffusion through open channel is passive and requires no energy
Equilibrium Potential (Single Ion)
-Diffusion potential that exactly balances or opposes the tendency for diffusion of an ion down its concentration gradient
-Equilibrium when chemical and electrical driving forces are EQUAL and OPPOSITE
-Magnitude of potential is DIRECTLY proportional to magnitude of concentration gradient
Na+ across plasma membrane
-Greater in the ECF (145) than ICF (12)
-Can passively cross the membrane through some protein channels, even at rest
K+ across the plasma membrane
-Greater in the ICF (150) than the ECF (4)
-Can passively cross the membrane through some protein channels, even at rest
-Much easier to cross the membrane b/c cell has more channels open for K+ than Na+
-At resting membrane potential, permeability 50-75x more greater
A- (neg charge ions) across plasma membrane
-ECF (110)
-ICF (4)
Potassium Equilibrium Potential
-Tends to be pushed out of cell via CONCENTRATION gradient
-Outside becomes more pos
-Anion can’t cross membrane, inside becomes more neg
-The resulting ELECTRICAL gradient moves K+ back into cell
-Net movement when gradients are counterbalanced
-Membrane potential for K+ (Ek+) = -90mV
Sodium Equilibrium Potential
-Na+ pushed into cell via CONCENTRATION gradient
-Inside of cell becomes more pos
-Outside of the cell becomes more neg
-ELECTRICAL gradient tends to move Na out of cell
-No further net movement occurs when gradients exactly counterbalance each other
-Equilibrium Potential for Na+ (Ena+) = 65mV
Nernst Equation
Used to calculate the equilibrium potential for an ion at given concentration difference across the membrane
Eion = (60/z) log([ion]out/[ion]in)
Eion = equilibrium potential for ion (mV)
Z = ionic valence for ion (charge + or -)
[ion]out = extracellular concentration for ion (mmol/L)
[ion]in = intracellular concentration for ion (mmol/L)
Resting Membrane Potential
-All living cells have the SAME resting membrane potential
-Constant membrane potential present in cells of non-excitable tissues
-RMP refers to the diff. that exists across the membrane of excitable cells at steady-state
-Nerve and muscle cells have the ability to produce rapid, transient changes when excited
Ohm’s Law / Goldman Equation
Estimates membrane potential knowing the equilibrium potentials and conductance (permeability) for each ionic species in question
Em = (gKEk + gNaEna) / (gK + gNa)
g = conductance depends on K channels being open or closed
E = equilibrium potential for ion
Sodium-Potassium Pump
-Role on Membrane potential is to maintain ion gradient
-Pump makes relatively small contribution to membrane potential
-Membrane potential is caused by the diffusion of K and Na down their concentration gradients through channels
What happens to RMP if ionic concentrations change?
-Changes are due to total ion concentrations in ECF & ICF
Increased ECF K+ (hyperkalemia) = depolarization
Increased ECF Na+ (hypernatremia) = depolarization
Decreased ECF K+ (hypokalemia) = hyperpolarization
Decreased ECF Na+ (hyponatremia) = hyperpolarization
