2 - Membrane Potential Flashcards
Is the intracellular or extracellular concentration higher for K+?
Intracellular
Is the intracellular or extracellular concentration higher for Na+?
Extracellular
Is the intracellular or extracellular concentration higher for Cl-?
Extracellular
Is the intracellular or extracellular concentration higher for Ca++
Extracellular (or intracellular if it is sequestered in the SER)
What does the strength of the chemical concentration gradient depend on?
The chemical that is diffusing and the membrane it is diffusing through
If an ion was responding to just a chemical force, how would it respond?
It would move down its concentration gradient
If an ion was responding to just the electrical potential, how would it move?
It would move its electrical gradient
What is the net effect of the electrical and chemical forces?
You can have equilibrium, slight diffusion or rapid diffusion
What happens to EK+ when the extracellular concentration of K+ is raised?
Remember that the intracellular concentration of K+ is typically higher than the extra cellular concentration
When the extracellular concentration of K+ is raised, the EK+ value is decreased
What happens to EK+ when the extracellular concentration of K+ is lowered?
Remember that the intracellular concentration of K+ is typically higher than the extra cellular concentration
When the extracellular concentration of K+ is lowered (lower than it already is), the EK+ value is increased
What happens to ENa+ when the extracellular concentration of Na+ is raised?
Remember that the extracellular concentration of Na+ is typically higher than the intracellular concentration
When the extracellular concentration of Na+ is raised, the ENa+ is increased
What happens to ENa+ when the extracellular concentration of Na+ is lowered?
Remember that the extracellular concentration of Na+ is typically higher than the intracellular concentration
When the extracellular concentration of Na+ is lowered, the ENa+ is decreased
What happens to the membrane potential if the extracellular K+ is raised?
The membrane potential is decreased
The cell is depolarized
What happens to the membrane potential if the extracellular K+ is lowered (more than it already is)?
The membrane potential is increased
The cell is hyperpolarized
What happens to the membrane potential if the extracellular Na+ is raised (more than it already is)?
The membrane potential is decreased (small effect)
The cell is depolarized (slightly)
What happens to the membrane potential if the extracellular Na+ is lowered?
The membrane potential is increased (small effect)
The cell is hyperpolarized
How does the membrane potential change when it becomes more permeable to K+?
Remember that as the relative permeability of the membrane to an ion increases, the membrane potential of the cell moves closer to the equilibrium potential of that ion
Depolarization of the cell
How does the membrane potential change when it becomes more permeable to Na+
Hyperpolarizes the cell
How does the membrane potential change when it becomes more permeable to Cl-?
Hyperpolarizes the cell
As the EK+ value decreases, the membrane potential __________.
Also decreases
As the ENa+ value decreases, the membrane potential __________.
Also decreases
The actual membrane potential is balanced between two values, what are they?
EK+ and ENa+
In the resting state, the cell is much more permeable to ____ than it is to _____.
More permeable to K+
Less permeable to Na+
What does this mean about the actual membrane potential?
It is closer to EK+ than it is to ENa+
During an action potential, the membrane becomes more permeable to ____.
Na+
The increased permeability to Na+ makes the actual membrane potential move closer to _____.
ENa+
So, in general, how is the membrane potential affected by its permeability?
If the membrane becomes more permeable to either sodium or potassium, the membrane potential of the cell becomes closer to the equilibrium potential for that particular ion
The well known sodium-potassium pump is “electrogenic” - what does that mean?
It changes the electric potential of the membrane
How does the Na+-K+ pump change the electric potential of the membrane?
It pumps 3 Na+ OUT of the cell for every 2 K+ is pumps INTO the cell
What is the net effect of the Na+-K+ proton pump on the membrane potential?
Over time, the membrane potential will become more negative or more hyperpolarized because more Na+ is going out than the K+ coming in (there is a net eflux of positive ions)
What is the MAIN role of the sodium-potassium pump?
Important
The role of the sodium-potassium pump is to maintain the membrane potential in an INDIRECT way - it is able to do this simply by maintaining the Na+ and K+ concentration gradients
What does it mean when a cell is at its resting membrane potential?
The cell is NOT at equilibrium but at a STEADY state
Describe the “steady state” of a resting membrane potential
The cell is “leaky”
- K+ is leaking out
- Na+ is leaking in
What balances the “leakiness” of the cell in order for it to maintain its resting membrane potential?
This “leakage” is EXACTLY balanced by the actions of the sodium-potassium pump that is pumping Na+ out and K+ in
This process of maintaining the membrane potential requires _________________.
Metabolic energy
What else does the sodium-potassium pump maintain?
Cell volume
How does the sodium-potassium pump also maintain cell volume?
By pumping sodium out of the cell, it decreases the osmotic pressure in the cytoplasm, which increases the osmotic pressure in the extracellular fluid
What is hyperkalemia?
High potassium
What is hypokalemia?
Low potassium
What is hypernatremia?
High sodium
What is hyponatremia?
Low sodium
What is hypercalcemia?
High calcium
What is hypocalcemia?
Low calcium
What does membrane polarization mean?
At rest, a cell has negative charges on the inside of the membrane and positive charges on the outside of the membrane
This makes the cell membrane POLARIZED
What does membrane depolarization mean?
Depolarization is when the membrane becomes less negative inside the cell (or more positive)
Example: the membrane potential would change from -80 mV to -50 mV due to an influx of positive ions into the cell
What does membrane hyperpolarization mean?
Hyperpolarization is when the membrane becomes more negative inside the cell
Example: the membrane potential changes from -80 mV to -90 mV
