Membrane potential Flashcards
What are the two ways in which ions are separated?
diffusion or through ion channels
What is the voltage at the outside of the cell?
Zero, by convention
The inside of a cell at
rest is always [blank] relative to the outside, so the cell’s membrane potential is a
[blank] number.
The inside of a cell at
rest is always negative relative to the outside, so the cell’s membrane potential is a
negative number.
What are the two forces that act on an ion?
The electric, and the chemical
What causes the electrical driving force?
unequal distribution of ions
If a cells membrane potential is negative, where will cations be drawn to?
Inside the cell
Assume that a cell membrane is only permeable to K. What will happen?
K will diffuse out until chemical and electrical forces are balanced.
What is the equilibrium potential of an ion, e.g. E(K+)?
The potential (V) of an ion
What is the Nernst equation?
Look at it!
Where does the membrane potential fall, relative to the equilibrium potentials for Na and K?
Between them, but closer to Ek d/t a higher number of K transporters
True or false: Ek changes with [K] changes
True
What happens when an action potential to the Na and K ions?
the membrane becomes more permeable to Na
When is the Goldman-Hodgkin equation used?
When there are several ions affecting the resting membrane potential
Look at the GHK equation
look at it
As the relative permeability of the membrane to an ion increases, the
membrane potential of the cell moves closer to what?
the equilibrium potential of that ion.
State whether the intracellular or the extracellular concentration is higher for the following ions: K+ Na+ Cl- Ca++
K+ - intracellular higher
Na+ -extracellular
Cl- extracellular
Ca++ - intracelllar
True or false: At resting potential, the cell is at an equilibrium
False - At the cell resting membrane potential, cell is NOT at equilibrium but at steady state. K+ is leaking out and Na+ is leaking in. This
leakage is exactly balanced by the Na+
-K+ pump that pumps Na+ out and K+
in. Metabolic energy is necessary to maintain ion gradients.
What is the chemical driving force?
The force on an ion to move down its concentration gradient
What is the electrical driving force?
Electrical force that ions exert
What is the equilibrium potential?
When the chemical driving force = the electrical driving force
What is the membrane potential?
The potential that a membrane exerts d/t separation of charges and varying degrees of permeability of the membrane
Why can we simplify the nernst equation and not take into account that particles are lost from the inside to the outside?
The number of ions that have to move to establish an equilibrium is extremely small
What is the principle of electric neutrality?
any macroscopic region
of a solution must have equal number of positive and negative charge
What maintains the concentration gradient when the cell is permeable to both potassium and Na?
Na/K pumps
Why is there a negative resting potential of cells when is it permeable to both K and Na?
K has more pumps, and the Na/K pumps, pumps out 3 Na for every 2 K brought in
What is the toxin that can inhibit the Na/K pump?
Ouabain
How fast does ouabain work?
gradually
What is the permeability coefficient of the goldman-Hodkin equation?
how well a given ion passes through a membrane–it is a constant
What happens in hyperpolarization?
Potential becomes more negative
What happens in depolarization?
Potential becomes more positive
What happens to the membrane potential if the permeability of an ion is increased?
the resting potential falls closer to that ion
Whenever ECl- is made more negative than the membrane potential, what is true?
the chemical force on the ion is
stronger than the electrical force exerted by the membrane potential
Do Ca ion contribute to resting membrane potential? Why or why not?
no, the membrane is not permeable
