NUR968 Membrane Potentials & Action
Potentials - Cell Signaling & Second Messenger
Systems Test With Solution
What is the membrane potential? - ANSWER Defined as the electrical
potential difference across a cell's plasma
How are ions classified? (2) - ANSWER 1. Cations (positively charged)
2. Anions (negatively charged)
Although all positive & negative charges establish membrane potential, what
are the 2 key players (ions)? - ANSWER 1. Sodium
2. Potassium
True or false: The net flux of ions is a continuous dynamic process (never
static) - ANSWER True
How much more permeable is the plasma membrane to potassium? -
ANSWER 100x more permeable
True or false: The Sodium Potassium ATPase Pump moves ions AGAINST
their concentration gradient - ANSWER True
The plasma membrane contains protein channels called "leak channels."
What do these do? - ANSWER They leak ions (they are always open)
Which ions are leaked is dependent on what 3 factors? - ANSWER 1. The
polarity of the electrical charge of the ion & the charge on either side of a
membrane
,2. The permeability or "selectability" (specificity) of the leak channels to an
ion
3. Concentration gradient on either side of the leak channel
With potassium & sodium, which ion has the greatest concentration INSIDE
the cell? What about OUTSIDE the cell? - ANSWER Inside = Potassium
Outside = Sodium
So, why is potassium (a cation) more likely to leak out of the cell? - ANSWER
Because of the permeability to potassium
-As potassium leaves, it takes with it a positive charge leaving the inside of
the cell "more negative". This negativity then pulls potassium back in
Recall from Module 1:
When the Sodium Potassium Pump runs, 3 Na+ move OUT; 2 K+ move IN.
What is happening inside/outside of the cell each time this happens? -
ANSWER The inside of the cell becomes more NEGATIVE & the outside
becomes more POSITIVE (Separation of Charges)
What is a key player in maintaining the concentration gradients?*** -
ANSWER Sodium Potassium Pump
-Overall, sodium is predominately on the outside of the cell
-Potassium is predominately kept on the inside
Nernst Equation
-Nobel prize in 1920
-Relates the __ __ to the electrical force
, -Electromagnetic force (EMF) __ diffusion despite the ion concentration
gradient
So what does the Nernst equation help us equate? - ANSWER Helps us
equate the potential created by separating ions across a membrane ("helps
us determine what the resting membrane potential is")
-Recall that electrical charges can oppose diffusion
So what is the Resting Membrane Potential (RMP)? - ANSWER The electrical
difference between the inside & the outside of the cell
What is potassium's concentration on the inside to the outside? - ANSWER
35 : 1
What is sodium's concentration on the inside to the outside? - ANSWER 0.1 :
1
True or false: If we took all of the ions on either side of the cell & ran them
through the Nernst equation & then added them up, we would theoretically
get the actual resting membrane potential - ANSWER True
Why is the Nernst Equation considered too simple or flawed? - ANSWER It
only takes into account two ions (sodium & potassium)
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