Membrane Potential

Potential (E)

separation of charge, Volts

gives ability to do work

Resting membrane potential def

at a steady state requires what to maintain?

Difference in charge between inside and outside of cell at rest

Continual work and energy

Depolarization

A change in the membrane potential so that it is closer to 0 (either from + or -)

Hyperpolarization

change in membrane potential so that it is further from 0

current

movement of charge (amps)

Resistance

Opposition to the flow of charge, (Ohms)

Ex: ion channels that are closed

Ohm’s law

V = IR (voltage = current * resistance)

Permeability

ease at which a particular ion moves through an open channel

Conductance

Ease of flow of current through an ion channel (opposite of resistance)

the resting membrane potential depends on what 3 things?

• Na/K+ ATPase: direct and indirect roles

• Distributions of ions across membrane

  • Na: high outside cell, low inside cell

  • K: high inside cell, low outside cell

• Membrane permeabilities of certain ions

electrogenic?

electrogenic: contributes to net electric charge difference

Na/K ATPase is electrogenic, as it pumps out 3 Na+, and in 2 K’s+, which means it has a net -1 charge in the cell (effect = +1 out of cell)

Na/K ATPase roles in resting membrane potential

Major contributor to indirect effect on Resting potential: Establishes gradients of Na and K

minor contributor: Direct effect on resting potential: net flow of charge +1 out of cell, makes inside 5-10 mv more negative

Na and K relative permeability

Na: 1

K: 50-75

electroneutrality

cations and anions must exactly balance

MP is due to a difference of charge at the membrane

Only a small number of ions need to move to change MP: T/F

True

Electrical vs chemical potential

Electrical: difference in charge of all charged particles

Chemical: difference in concentration outside vs inside a cell of an ion

What is balanced at equilibrium?

electrical gradient vs concentration gradient (K moves out of cell, which makes it less positive, moves back into cell)

Equilibrium reversal potential

Membrane Potential at which no net flux of an ion occurs

The voltage at which the direction of ion through a channel is reversed is when?

Equilibrium reversal potential

nernst equation at 37 degrees C

61/z(charge)* log (conc out/conc in)

(if taking log of greater than 1: positive result, if between 0 and 1: negative)

what would Nerst equation of -90 mV mean

At -90 mV, the chemical gradient of K trying to leave the cell (as it has higher conc in cell) would be perfectly balanced by K trying to enter the cell to balance out the charge

• more negative than -90 mV : K moves in

• more positive than -90 mV: K moves out

Ion permeability: increasing the membrane permeability of a particular ion will drive the membrane potential toward ?

positive ions: potentials more negative than its Erev will cause?

negative ions: potentials more negative than its Erev will cause?

the equilibrium potential of that ion

net influx

net outflux

what has the biggest effect on resting membrane potential?

K

why is the resting potential more depolarized compared to K equilibrium potential?

K: -94, Na: +60, the Na leaks in and makes it more depolarized, but K still dominates as its resting permeability is much more

The smaller the Na permeability…

the closer Em will be to Ek