Lecture 5: Membrane Potentials and the Goldman Equation

What causes the neuronal electrical potential and when is it active?

It is caused by the separation of charges across the membrane and it is active at all times

T/F: The electrical potential stops during the peak of the action potential

False. It is active at all times

What are the two things that the Nernst equations predicts will generate a potential?

1. There are concentration difference in ions separated by a membrane
2. At least one of those ion species is permeable, or can move across the membrane

What does the potential across a membrane depend on?

* differences in concentrations of specific ions across nerve cell membranes
* How permeable, or are free to cross the membrane that an ion species is

How is tight control of electrical signaling allowed?

It is allowed because of the tight control of differences in concentrations of ions and permeability of the membrane

Which ion is mostly limited to the outside of the cell?

Sodium (Na+)

Which ion is much more concentrated on the inside of the cell?

Potassium (K+)

What do Na+ and K+ pumps mainly do?

They move Na+ that is in the cell, out, and the K+ that is out of the cell, back in

What do the pumps of the ions Na+ and K+ produce?

The concentration gradient for each of the ions

T'/F: Concentration gradients change substantially overtime

False

At rest, which ion is the only ion that the cell membrane is permeable too? What does that mean?

It is permeable to K+ only (mostly) which means that only K+ can influence the membrane potential at that time

What happens when only one ion species is permeable?

The membrane potential will be driven to that species equilibrium potential

Whats the Nernst (Equilibrium) Potential for K+, Na+, and Cl-?

K+ = -75

Na+ = 50

Cl - = -60

How do we know the resting potential is due to K+?

If we increase the extracellular concentration of K+, then this should influence the resting membrane potential in a predictable way (in proportion to the log K+ in vs. K+ out)

* K+ in stays constant

How do we know that the action potential is due to Na+ permeability?

* take away extracellular Na+, action potential is reduced
* If there is no extracellular sodium, it can’t flow through the membrane to create an action potential
* If we decrease the difference in sodium concentration inside and outside the cell, the equilibrium potential goes down

Does extracellular Na+ concentration affect the height of the action potential?

Yes. The lower the extracellular Na+ concentration, the lower the height of the action potential

How does sodium affect membrane potential?

As sodium enters, the membrane potential of the cell decreases and becomes more positive