1. What is the Nernst Equation?

The Nernst equation calculates the equilibrium potential for an ion across a membrane - the membrane potential at which there is no net flow of that particular ion. It's fundamental in understanding cellular electrophysiology.

2. How Does the Calculator Work?

The calculator uses the Nernst equation:

Where:

• \( E_{eq} \) — Equilibrium potential (mV)
• \( R \) — Universal gas constant (8.314 J/mol·K)
• \( T \) — Absolute temperature (K)
• \( z \) — Valence of the ion
• \( F \) — Faraday's constant (96485 C/mol)
• \( [out] \) — Extracellular concentration (mM)
• \( [in] \) — Intracellular concentration (mM)

Explanation: The equation calculates the membrane potential that exactly balances the concentration gradient for a specific ion.

3. Importance of Equilibrium Potential

Details: Understanding equilibrium potentials is crucial for studying action potentials, synaptic transmission, and membrane transport processes in cells.

4. Using the Calculator

Tips: Enter ion concentrations in mM, valence as integer (+1 for Na+, +2 for Ca2+, -1 for Cl-, etc.), and temperature in °C. All values must be valid (concentrations > 0, valence ≠ 0).

5. Frequently Asked Questions (FAQ)

Q1: What are typical values for common ions?
A: Na+ (~+60mV), K+ (~-90mV), Ca2+ (~+120mV), Cl- (~-70mV) in mammalian cells at 37°C.

Q2: Why does temperature matter?
A: The Nernst equation depends on thermal energy (RT), so results vary with temperature.

Q3: What if my ion is divalent?
A: Use z=2 for Ca2+ or Mg2+, which will halve the potential compared to monovalent ions.

Q4: What about anions vs cations?
A: Use negative z values for anions (like Cl-), which reverses the sign of the potential.

Q5: How does this relate to resting membrane potential?
A: Resting potential is a weighted average of all permeable ions' equilibrium potentials.