Establishing Resting Membrane Potential
📌 The resting membrane potential is established by differences in ion concentration and charge across the cell membrane, as well as membrane permeability.
💧 Key concentration differences include higher $\text{Na}^+$, $\text{Cl}^-$, and $\text{Ca}^{2+}$ outside the cell, and higher $\text{K}^+$ and negative anions ($\text{A}^-$) inside.
🛠️ The sodium-potassium pump maintains gradients by moving three $\text{Na}^+$ ions out for every two $\text{K}^+$ ions moved in, utilizing ATP.

Ion Equilibrium Potential (Nernst Potential)
⚖️ The equilibrium potential for an ion is reached when the outward concentration gradient force equals the inward electrostatic gradient force.
🔑 For $\text{K}^+$, this equilibrium potential is approximately -92 mV, balancing its high internal concentration against the negative charge attracting it back inside.
🧪 The equilibrium potential ($V_m$) for a single-charge ion is calculated using the Nernst equation: $V_m = 61.5 \times \log \left(\frac{[\text{Ion}]_{\text{out}}}{[\text{Ion}]_{\text{in}}}\right)$.

Calculating Resting Membrane Potential
📊 For ions with double charges like $\text{Ca}^{2+}$, the equation uses a different multiplier: $V_m = 30.75 \times \log \left(\frac{[\text{Ion}]_{\text{out}}}{[\text{Ion}]_{\text{in}}}\right)$.
📉 Based on typical concentrations, the equilibrium potentials for $\text{K}^+$, $\text{Na}^+$, $\text{Cl}^-$, and $\text{Ca}^{2+}$ are $\mathbf{-92 \text{ mV}}$, +67 mV, -86 mV, and +123 mV, respectively.
🌐 The actual resting membrane potential is a weighted sum of these individual equilibrium potentials, determined by the relative permeability of each ion through the membrane channels.

Key Points & Insights
➡️ $\text{K}^+$ permeability generally dominates, making the resting membrane potential closest to the $\text{K}^+$ equilibrium potential (e.g., -86 mV in the example calculation).
➡️ Changing the cell's permeability to specific ions (by adding or removing ion channels) is the mechanism by which a cell can alter its resting membrane potential.
➡️ The resting membrane potential is fundamentally a summation based on each ion's relative permeability across the membrane.

📸 Video summarized with SummaryTube.com on Oct 27, 2025, 14:32 UTC