1. What is the Nernst Equation?

The Nernst equation calculates the equilibrium potential for an ion across a membrane based on its concentration gradient. It's fundamental for understanding electrical signaling in neurons and other excitable cells.

2. How Does the Calculator Work?

The calculator uses the Nernst equation:

Where:

• \( V_m \) — Membrane potential (mV)
• \( R \) — Universal gas constant (8.314 J/mol·K)
• \( T \) — Absolute temperature (K)
• \( z \) — Valence of the ion (1 for Na+, K+; 2 for Ca2+)
• \( F \) — Faraday's constant (96485 C/mol)
• \( [out] \) — Extracellular concentration (mM)
• \( [in] \) — Intracellular concentration (mM)

Explanation: The equation shows how the electrical potential balances the concentration gradient for a specific ion.

3. Importance of Membrane Potential

Details: Membrane potentials are crucial for nerve impulses, muscle contractions, and cellular signaling. Different ions (Na+, K+, Ca2+, Cl-) have different equilibrium potentials.

4. Using the Calculator

Tips: Enter concentrations in mM, temperature in °C, and select ion type. Typical values for neurons: K+ (out=5, in=150), Na+ (out=145, in=12).

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between Nernst and Goldman equations?
A: Nernst calculates equilibrium potential for one ion, while Goldman calculates resting membrane potential considering multiple ions.

Q2: Why is potassium important for membrane potential?
A: K+ has the greatest permeability at rest, so resting potential is closest to E_K (-70 to -90 mV).

Q3: How does temperature affect membrane potential?
A: Higher temperature increases the potential magnitude slightly (RT/F term).

Q4: What are typical values for common ions?
A: E_Na ≈ +60 mV, E_K ≈ -90 mV, E_Ca ≈ +120 mV, E_Cl ≈ -65 mV.

Q5: When is the Nernst equation not applicable?
A: When multiple ions contribute significantly to the potential, or when active transport (pumps) are involved.