Review Nernst and Goldman Equations

Whenever you change the inside ion concentration, the Vm always increases. If you change the outside ion concentration, the Vm will always decrease. A. True B. False

B. False Depends on charge of an ion. If you increase the inside concentration of a negative ion then the log value increases and the membrane potential increases. For negative ions, take the log value of the inside/outside ion concentration times P.

When simplifying the Nernst equation, the number over z will always be 58. A. True B. False

B. False Only at 19 deg C. A change in temperature will change this number.

Vm is ... A. for each ion B. sum for all ions

B. sum for all ions

At a Vm of +50mV, which of the following is likely to occur? Vrest= -65mV ENa= +50mV Ek= -80mV A. The driving force on sodium is relatively high B. The sodium current is relatively high C. All of the above D. None of the above

D. None of the above. Vm is equal to ENa. By definition, at Ex DF=0 and I=0.

Under normal biological condition, how could a cell move its membrane potential to -150mV? Vrest= -65mV ENa= +50mV Ek= -80mV A. Open all K+ channels B. Open all Na+ channels C. Close all the K+ channels D. Close all Na+ channels E. None of the above

E. None of the above. If you open all the K channels, Vm--> Ek = -80mV. But it wouldn't go any lower. If you open all Na channels, Vm--> ENa = +50. If you close all the channels then Vm wouldn't change at all.

How does increasing the temperature affect Vm?

Increasing temperature will decrease Vm. As temperature decreases, Vm increases (less negative). (e.g. at 37 deg Vm=-59.2, at 19 deg Vm= -55.8)

Does the Vm change 10 fold with each 10 fold change in PNa+ or PK+?

No. A 10 fold change in Px causes less than a 10 fold change in Vm. This is because there are many types of ions that affect Vm.

According to the Goldman equation, does a ten fold increase in outside concentration change Vm by 58 mV?

Not always. Vm is affected by the concentrations and permeabilities of multiple ions.

According the the Goldman equation, when the inside concentration of a positive ion increases...?

The log value decreases so Vm decreases.

According the the Goldman equation, when the outside concentration of a positive ion increases...?

The log value increases so Vm increases.

The Nernst equation can be used to determine:

The membrane potential at which there is no net current for an ion.

What is the definition of Ex?

The membrane potential at which there is no net current for an ion.

What is the Goldman equation?

Vm= 58 log (P outside ion/P inside ion) + each ion

How can changing the Px have the opposite effect of changing Py?

Will have to do with relative outside and inside concentrations, the equilibrium potentials and the DF. The equilibrium potentials are equal and opposite to each other. The greater the permeability for an ion, the closer Vm is to the Ex for that ion.

Using the Nernst Equation, how does Ek change when extracellular K+ changes from 5 to 50 mM?

A ten fold increase in outside concentration of K will increase the Vm by 58mV.

Ex is A. specific for each ion B. the sum of all ions

A. specific for each ion

How might running a fever (i.e. increased temperature) affect the function of the nervous system?

As temperature increases, Vm of neurons will decrease, making it more difficult to fire an action potential.

At Ex, how does ion x move?

At Ex, there is no net movement of ion x.

If the permeability for potassium is raised by 20 fold and the conductance for sodium is raised by 10 fold, what will happen to the resting membrane voltage? A. The Vm would increase by 10 fold. B. The Vm would increase by 30 fold. C. The Vm would increase by multiple of 58 mV. D. The Vm would decrease by multiple of 58 mV. E. None of the above.

E. none of the above Use the Goldman equation. Permeability is the same as conductance. Permeability only partially contributes to Vm. There is no ten fold rule for Goldman equation.

Nernst Equation

Ex= 58/z log (outside/inside)