3.1: Origin of the Resting Membrane Potential

Equilibrium Potential

for a given ion, is the membrane potential at which the net flow of that ion across open channels is zero

At EQ potential

- The electrical force exactly balances the diffusive force for the ion (no net driving force)
- The electrochemical potential difference between the two sides of the membrane is zero for the ion.

Resting membrane potential

occurs when the net current across the membrane is zero (steady-state)

Membrane potential arises when...

there is an uneven distribution of ions between the inside and the outside of the cell, and from the difference in the permeability of the membrane to different types of ions.

Negative/inward current =

positive charges enter the cell

Positive/outward current =

positive charges exit the cell

Conductances relate

membrane potential to ion flow/fluxes.

Conductances are not ____, they vary with ___

constant; Em

Conductance and permeability are ____

directly related.

if the concentration gradient is positive, the

diffusive force is negative/inward

Why are cell membranes more permeable to K+ than Na+?

They have more K+ leak channels than Na+ leak channels.

Slope conductance vs Chord conductance

The chord conductance characterizes the ionic permeability of the membrane while the slope conductance reflects an electric property directly affecting the membrane input resistance.

What happens to the membrane potential when the conductance to a particular ion changes?

The membrane potential also changes. The greater the conductance of an ion, the more that ion will influence the membrane potential of the cell.

What is the current of an ion at its equilibrium potential?

zero

If Cl- enters the cell, does it make a positive or negative current?

Influx of negative charges = efflux of positive charges, so a positive current

If the conductances of the membrane to K+ were increased, what would happen to Ek? to Em?

No changes to Ek, and Em would move closer to Ek

If a cell’s membrane carries a negative electric potential (voltage), the cell’s surroundings are more _____________ charged than the cell’s interior.

positively

As ions flow across a membrane, they drive the membrane potential toward the ____________ potential of the ion

equilibrium

What are the variables in the “definition of the chord conductance” equation Ii = gi (Em - Ei)?
i is the ion symbol.
Ii is the ______ of ion i through the membrane.
gi is the chord conductance of ion i
Em is the _______ potential
Ei is the ______ potential for ion i

current; membrane; equilibrium

The sodium-potassium pump uses ATP to actively move ____ Na+ ions out of a cell, and ____ K+ ions into the cell. This would cause the cell membrane to have a _____ electric potential.

3 ; 2; negative