# Help: Nernst and reversal potentials

In summary, the Nernst equation is a mathematical formula used to calculate the equilibrium potential of an ion across a membrane, taking into account the concentration gradient, temperature, and charge of the ion. The Nernst potential is significant because it represents the voltage at which there is no net flow of ions across the membrane, and is important in determining the resting membrane potential and excitability of cells. It is related to the reversal potential, which refers to the point at which the membrane potential changes direction. The Nernst potential is affected by various factors, such as ion concentration gradient, temperature, and charge, and is used in biological systems to determine resting membrane potential and understand ion movement and its impact on cellular processes.
I know the following
ion/inside cell/outside cell
Cl- 5mM 150 mM
K+ 130mM 5mM
Na+ 20mM 140mM
Ca2+ 10^-4mM 2mM

How would I find the reversal potential for conductance equally permeable to sodium and potassium?
How do I find the reversal potential for a conductance equally permeable to sodium, potassium, and chlorine?
Also, how do I find the nernst potential for each ion at the below external and internal concentrations?

bump- for great justice!

To find the reversal potential for conductance equally permeable to sodium and potassium, you would use the Goldman-Hodgkin-Katz equation, which takes into account the concentrations and permeabilities of each ion. In this case, the reversal potential would be around -50mV, which is the average of the Nernst potentials for sodium (-61mV) and potassium (-89mV).

For a conductance equally permeable to sodium, potassium, and chlorine, you would again use the Goldman-Hodgkin-Katz equation, but this time also taking into account the permeability of chloride. The reversal potential would be around -65mV, which is the average of the Nernst potentials for sodium, potassium, and chloride (-35mV, -89mV, and -61mV, respectively).

To find the Nernst potential for each ion at the given concentrations, you would use the Nernst equation, which takes into account the charge and concentrations of the ion. For Cl-, the Nernst potential would be around -63mV; for K+, it would be around -86mV; for Na+, it would be around +61mV; and for Ca2+, it would be around +120mV. These values represent the equilibrium potential for each ion, where there is no net movement of the ion across the membrane.

## 1. What is the Nernst equation and what does it calculate?

The Nernst equation is a mathematical formula used to calculate the equilibrium potential of an ion across a membrane. It takes into account the concentration gradient, temperature, and charge of the ion to determine the potential at which there will be no net movement of ions across the membrane.

## 2. What is the significance of the Nernst potential?

The Nernst potential is important because it represents the voltage at which the electrochemical gradient of an ion is balanced, meaning there is no net flow of ions across the membrane. This is a key factor in determining the resting membrane potential and the excitability of cells.

## 3. How is the Nernst potential related to the reversal potential?

The Nernst potential and the reversal potential are often used interchangeably, as they both refer to the same concept of the equilibrium potential for an ion. The reversal potential specifically refers to the point at which the membrane potential changes direction, from being more negative to more positive, as the concentration gradient of the ion changes.

## 4. What factors affect the Nernst potential?

The Nernst potential is affected by the concentration gradient of the ion, the temperature, and the charge of the ion. Other factors that can influence the Nernst potential include the presence of other ions, channel permeability, and changes in the membrane potential.

## 5. How is the Nernst potential used in biological systems?

The Nernst potential is used in biological systems to determine the resting membrane potential of cells, which is important for maintaining cell function and communication. It is also used to understand the movement of ions across cell membranes and how changes in the Nernst potential can affect cellular processes such as muscle and nerve cell activity.

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