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 in understanding membrane potentials in cells, particularly in neuroscience and physiology.

2. How Does the Calculator Work?

The calculator uses the Nernst equation:

Where:

• \( E \) — Nernst potential (mV)
• \( R \) — Gas constant (8.314 J/mol·K)
• \( T \) — Absolute temperature (K)
• \( z \) — Ion charge (dimensionless)
• \( F \) — Faraday's constant (96485 C/mol)
• \( [out] \) — Extracellular concentration (mM)
• \( [in] \) — Intracellular concentration (mM)

Explanation: The equation calculates the membrane potential at which the electrical and chemical gradients for an ion are balanced.

3. Importance of Nernst Potential

Details: Nernst potentials are crucial for understanding resting membrane potentials, action potentials, and synaptic transmission in excitable cells like neurons and muscle cells.

4. Using the Calculator

Tips: Enter concentrations in mM, temperature in Kelvin (310K = 37°C), and ion charge (e.g., +1 for Na⁺, -1 for Cl⁻). All values must be positive, and charge cannot be zero.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical Nernst potential for K⁺?
A: With [K⁺]out = 5 mM and [K⁺]in = 140 mM at 37°C, E_K ≈ -90 mV.

Q2: Why is temperature important?
A: The Nernst potential is directly proportional to absolute temperature. Physiological calculations typically use 310K (37°C).

Q3: How does ion charge affect the potential?
A: The potential is inversely proportional to charge. A divalent ion (z=2) will have half the potential of a monovalent ion with the same concentration ratio.

Q4: What if concentrations are equal?
A: When [out]=[in], the potential is 0 mV as there's no concentration gradient.

Q5: How does this relate to the Goldman equation?
A: The Goldman equation extends the Nernst concept to calculate membrane potential considering multiple permeable ions.