Membrane potentials Flashcards
What is resting membrane potential?
RMP is the electrical gradient across the membrane.
What is membrane potential?
The voltage across the membrane at any moment.
Can change over time.
Typical Vm at rest is -70mV.
What does the cell membrane do?
Cell membrane is impermeable to hydrophilic particles.
Cell membrane influences the composition of the intracellular environment.
Establishes a distinct internal environment (specific cations and anions).
What are the concentrations of ions in and outside of the cell?
Na+ - low inside, high outside
K+ high inside, low outside
Cl- low inside, high outside
Ca2+ low inside, high outside
What are the chemical gradients across the membrane?
An open channel for Na+ would mean Na+ moves down concentration gradient into the cell, bringing in a positive charge.
K+ would go out the cell and leave a negative charge.
How is the ionic gradient maintained?
The Na+K+ATPase ion pump uses ATP to pump ions against their concentration gradient to establish and maintain ionic concentrations.
How does K+ move into the cell?
When the K+ channel is open, K+ moves out of the cell, leaving a negative charge behind.
The negative charge then attracts K+ back into the cell.
No net movement K+ is the equilibrium potential of K+ (EK+), and there is a balance of electrical and concentration gradient).
What is membrane permeability?
The ease of an ion to move across the membrane.
How is an electrical potential difference across the membrane generated?
The membrane is more permeable to K+, so there is a negative charge at Vm, because it is close to K+.
How does the concentrations of ions in the membrane change?
The bulk concentration of ions does not change, because only a small concentration of ions moves at one time.
The amount the ions moves across the membrane depends on membrane potential and the equilibrium potential of the ion.
What is electrical neutrality?
Inside and outside the cell the anions and cations are balanced so there is a neutral charge.
The membrane potential is close to the inside membrane so can be measured.
What is equilibrium potential?
When there is no net movement of an ion (Eion).
This is the point at which an ion can maintain equal and opposite forces.
What is the Nernst Equation?
Determines Equilibrium potential.
see picture
How can the Nernst equation be simplified?
At 37.C:
Just need to know the concentration of the ion inside and outside the cell.
see picture
What is the Equilibrium potential for the ions?
If the cell was only permeable to each specific ion:
K+ is -80mV.
Na+ is +62mV.
Cl- is -65mV.
Ca2+ is +123mV
Why are the equilibrium potentials of each ion the particular sign?
K+ is high inside cell so moves out and leaves negative charge.
Na+ moves in and brings positive charge.
Cl- moves in and brings negative charge.
Ca2+ moves in and brings positive charge.
Why is the membrane potential -70mV?
-70mV because it is most permeable to K+, but also permeable to other ions.
Na+ which is +60mV leaks in so Vm is slightly more positive.
What is the Goldmann equation?
Calculates membrane potential when considering all the ions:
The sum of permeability of each ion determines Vm.
see picture
What happens when the ECF ion concentrations change?
Hypokalemia - reduced [K+] outside the cell, more K+ efflux, Vm more negative.
Hyperkalemia - increased [K+] outside the cell, less drive to reach equilbrium, Vm more positive.
