Nernst and Goldman Equations Quiz

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Questions and Answers

What ions are primarily involved in the Goldman equation for calculating membrane potential?

Chloride, Magnesium, and Sodium

Sodium, Potassium, and Chloride (correct)

Calcium, Sodium, and Potassium

Potassium, Chloride, and Calcium

What happens to the membrane potential if the membrane has zero permeability to sodium and chloride ions?

It becomes dominated by the concentration gradient of sodium.

It will show equal contribution from all ions.

It becomes equal to the Nernst potential for sodium.

It becomes entirely dominated by potassium concentration gradient. (correct)

What effect does a positive ion concentration gradient from inside to outside the membrane have?

It creates a neutral potential across the membrane.

It increases the permeability of chloride channels.

It causes electronegativity inside the membrane. (correct)

It results in a positive potential inside the membrane.

During the transmission of a nerve impulse, how do the sodium and potassium channel permeability change?

They undergo rapid changes. Signup and view all the answers

How does a chloride ion gradient from the outside to inside affect membrane potential?

It causes negativity inside the cell. Signup and view all the answers

What is primarily responsible for signal transmission in neurons?

Rapid changes in sodium and potassium permeability. Signup and view all the answers

In which type of cells is the membrane potential continuously changing?

Cardiac pacemaker cells Signup and view all the answers

What does the Goldman equation help determine regarding nerve and muscle fibers?

The calculated membrane potential based on ion concentration. Signup and view all the answers

What does the Nernst potential represent?

The diffusive potential that opposes the net diffusion of a specific ion Signup and view all the answers

Which factor does NOT influence the magnitude of the Nernst potential?

The permeability of the membrane to that ion Signup and view all the answers

In the Nernst equation, what does the variable 'z' represent?

The electrical charge of the ion Signup and view all the answers

If the concentration of potassium ions inside the cell is 10 times greater than outside, what is the Nernst potential inside the membrane?

−61 millivolts Signup and view all the answers

What does the Goldman equation help to calculate?

The overall diffusion potential when multiple ions are involved Signup and view all the answers

What is assumed about the potential outside the membrane when using the Nernst equation?

It remains at zero potential Signup and view all the answers

How does the sign of the Nernst potential change for positive and negative ions?

It is determined by the direction of ion diffusion Signup and view all the answers

Which of the following factors does the Goldman equation NOT take into account when calculating diffusion potential?

Membrane thickness Signup and view all the answers

Study Notes

Nernst Equation

The Nernst potential is the diffusion potential across a membrane that exactly opposes the net diffusion of a particular ion through the membrane.
The magnitude of the Nernst potential is determined by the ratio of the concentrations of that specific ion on the two sides of the membrane.
The greater this ratio, the greater the tendency for the ion to diffuse in one direction and therefore the greater the Nernst potential required to prevent additional net diffusion.
The Nernst equation can be used to calculate the Nernst potential for any univalent ion at the normal body temperature of 98.6°F (37°C):
- EMF millivolts = ± 61 × (log(Concentration inside/Concentration outside) / z)
- where EMF is the electromotive force and z is the electrical charge of the ion.
- The sign of the potential is positive (+) if the ion diffusing from inside to outside is a negative ion, and it is negative (−) if the ion is positive.

Goldman Equation

The Goldman equation (or Goldman-Hodgkin-Katz equation) is used to calculate the diffusion potential when the membrane is permeable to several different ions.
The formula for the Goldman equation for two univalent positive ions - sodium (Na+) and potassium (K+) - and one univalent negative ion - chloride (Cl−):
- EMF millivolts = -61 × (log((CNa(i) * PNa + CK(i) * PK + CCl(o) * PCl) / (CNa(o) * PNa + CK(o) * PK + CCl(i) * PCl)))
- Where:
  - CNa(i): Sodium inside
  - CNa(o): Sodium outside
  - PNa: Sodium Permeability
  - CK(i): Potassium inside
  - CK(o): Potassium outside
  - PK: Potassium permeability
  - CCl(i): Chloride inside
  - CCl(o): Chloride outside
  - PCl: Chloride permeability
The Goldman equation shows that:
- Sodium, potassium, and chloride ions are the most important ions involved in the development of membrane potentials in nerve and muscle fibers, as well as in the neuronal cells.
- The concentration gradient of each of these ions across the membrane helps determine the voltage of the membrane potential.
- The quantitative importance of each of the ions in determining the voltage is proportional to the membrane permeability for that particular ion.
- If the membrane has zero permeability to sodium and chloride ions, the membrane potential becomes entirely dominated by the concentration gradient of potassium ions alone, and the resulting potential will be equal to the Nernst potential for potassium. The same holds true for each of the other two ions if the membrane should become selectively permeable for either one of them alone.
- A positive ion concentration gradient from inside the membrane to the outside causes electronegativity inside the membrane because excess positive ions diffuse to the outside when their concentration is higher inside than outside the membrane. This diffusion carries positive charges to the outside but leaves the non-diffusible negative anions on the inside, thus creating electronegativity on the inside.
- The opposite effect occurs when there is a gradient for a negative ion. That is, a chloride ion gradient from the outside to the inside causes negativity inside the cell because excess negatively charged chloride ions diffuse to the inside while leaving the non-diffusible positive ions on the outside.

Resting Membrane Potential

In some cells, such as the cardiac pacemaker cells, the membrane potential is continuously changing, and the cells are never “resting”.
In other cells, even excitable cells, there is a quiescent period in which a resting membrane potential can be measured.
The resting membrane potentials of different cell types vary.
Rapid changes in sodium and potassium permeability are primarily responsible for signal transmission in neurons.

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Description

Test your knowledge on the Nernst and Goldman equations, essential concepts in understanding ion potential and membrane dynamics. This quiz covers the calculations, applications, and implications of these equations in biological systems. Enhance your understanding of electrochemistry and its role in physiology.