Lecture 3: Resting Membrane Potential Flashcards
How membrane potential is measured (units)
Millivolts
What allows membrane potential to do its work
Separation of opposite charges across membrane
What causes membrane potential
Differences in concentration and permeability of key ions
Charge of the inside of the cell
Negative
Charge of the outside of the cell
Positive
Where are separated charges arranged
Near cell membrane
Magnitude of membrane potential is proportional to
Number of charges
Ion channels: definition
Polypeptide chains that form water filled pores
Are ion channels selective
Yes
4 types of ion channels
-carrier
-undated
-ligand gated
-voltage gated
In the absence of a stimulus, ion channels can be
Ungated or leaky
Carrier ion channel: how it works
-Material carried by transport protein that binds tightly to material
-complex moves through lipid bilayer
Ungated channel: how it works
-allow certain ion to leak through pore
Ligand gated ion channel: how it works
-transport protein forms pore through membrane
-access to pore is controlled by gate
-opening and closing of gate is controlled by binding of ligand to channel
Voltage gated channels: how it works
-opening and closing of gate controlled by electrical field around channel
2 types of driving forces for diffusion of ions through open channel
-chemical
-electrical
What causes electrochemical gradient
Combination of chemical and electrical forces
Is diffusion of ion through an open channel a passive or active process
Passive
What will happen in a cell where membrane is permeable to K+ but not Cl- (3)
-Cl remains in cytosol but K+ diffuses across membrane inside cell
-will get greater negative charge inside cell
-influx of K+ containers until electrochemical equilibrium for K+ is reached
Equilibrium potential for single ion: definition
Diffusion potential that exactly balances or opposes the tendency for diffusion of an ion down its concentration gradient
When is an ion in equilibrium
When chemical and electrical driving forces are equal and opposite
Which ion is the most permeable
K+
What is the Nernst equation used for
Calculate equilibrium potential for an ion at a given concentration difference across membrane
What is one assumption of Nernst equation
Membrane is permeable to ion
What does Nernst equation determine
Electrical force required to just balance a given diffusion force
Nernst equation: alphanumeric
Eion = (60/z)log([ion]out / [ion]in)
Nernst equation: meaning of symbols
Eion = equilibrium potential for ion (mV)
Z = ionic valence for ion
[ion]out = extracellular concentration for ion
[ion]in = intracellular concentration for ion
What causes an ion to have 0 membrane potential
No permeability
Which ion has the greatest influence on resting membrane potential and why (Na+ vs K+)
K+ because of leaky ion channels (highest permeability)
Ohm’s law aka
Goldman equation
What does ohm’s law/Goldman equation estimate
Membrane potential knowing the equilibrium potential and conductive for each ionic species in question
2 main symbols in ohm’s law/Goldman equation
G = conductance
E = equilibrium potential
Ohm’s law/Goldman equation: alpha numeric
Em = (g of ion x E of ion) + (g of ion x E of ion) + … / (g of ion + g of ion + …)
Ohm’s law/Goldman equation: symbols explained
Membrane potential = sum of (conductance x equilibrium potential for each ion) divided by total conductance
Simplified version of resting membrane potential equation/ohm’s law (Since we focus on Na+ and K+)
‘Em = (gKEK + gNaENa) / (gK + gNa)
Hyperpolarization
-when membrane potential becomes more negative or closer to equilibrium potential of ion
Hypokalemia definition
Decreased potassium in ECF
Hypokalemia: clinical correlation with resting membrane potential
-leads to hyper polarized RMP
-muscle cells can’t contract properly
-leads to paralysis, diaphragmatic suffocation, asystole
Role of sodium potassium pump on membrane potential
Maintain ion gradient
Na/K pump: Membrane potential is caused by
Diffusion of K+ and Na+ down concentration gradients through ion channels
Increased ECF K+ called
Hyperkalemia
Hyperkalemia leads to (depolarization or hyperpolarization)
Depolarization
Hyponatremia definition
Decreased ECF Na+
Hyponatremia leads to (hyperpolarization or depolarization)
Hyperpolarization
Hypernatremia leads to (hyperpolarization or depolarization)
Depolarization
