📊 Understanding the Displays

Oscilloscope (Bottom Panel)

Green trace : Normal membrane potential (below -60mV)

Red trace : Action potential (above -60mV threshold)

Red dashed line : Fixed threshold at -60mV

Yellow sweep line: Current recording position

Membrane Potential Graph (Right Panel)

Red dashed line : Action potential threshold (-60mV, fixed)

Red dotted line : Sodium equilibrium potential (ENa, ~+60mV, moves with concentrations)

Blue dotted line : Potassium equilibrium potential (EK, ~-90mV, moves with concentrations)

⚡ Creating Action Potentials

Step-by-Step:

1. Set stimulus strength to 50-70 mV

2. Click "Stimulate" button

3. Watch voltage rise above -60mV threshold

4. Observe the complete spike cycle: depolarization → repolarization → hyperpolarization

Troubleshooting:

• If no spike occurs: increase stimulus strength or Na⁺ channel permeability

• For bigger spikes: increase Na⁺ permeability

• For longer spikes: decrease K⁺ permeability

🔬 Ion Channels & Transport

Voltage-Gated Channels:

Na⁺ channels (red ions): Open rapidly above -60mV, cause depolarization

K⁺ channels (blue ions): Open slowly above -60mV, cause repolarization

Leak channels: Always open, allow mixed ion flow

Green channels: Open and allow ion passage

Gray channels: Closed, block ion flow

Na⁺/K⁺ Pumps (5 purple pumps numbered 1-5):

Function: Transport 3 Na⁺ out for every 2 K⁺ in

Energy: Uses ATP (yellow pulsing circles)

Purpose: Maintains concentration gradients

Animation: Red arrows (Na⁺ out), blue arrows (K⁺ in)

🎛️ Control Panel Guide

Ion Channel Permeability:

Na⁺ Channels: Controls action potential amplitude (default: 0.04)

K⁺ Channels: Controls repolarization speed (default: 1.0)

Cl⁻ Channels: Minor effect on resting potential (default: 0.05)

Ion Pump Activity:

Pump Rate: Speed of Na⁺/K⁺ gradient maintenance (0-3x normal)

Temperature: Affects ion movement speed (20-40°C)

Stimulation:

Stimulus Strength: Depolarization amount (0-100 mV)

Offset: Shifts display by ±100mV (simulates measurement artifacts)

📈 Reading the Data

Current Status Panel:

Voltage: Current membrane potential (includes offset)

Phase: Current state (Resting, Depolarizing, Action Potential, etc.)

Na⁺ Conductance: Whether sodium channels are open

Ion Flux: Rate of ion movement across membrane

Ion Concentrations:

Shows real-time Na⁺, K⁺, and Cl⁻ levels inside and outside the cell

Equilibrium potentials (ENa, EK) update based on these concentrations

🧪 Experimental Ideas

• Block Na⁺ channels: Set Na⁺ permeability to 0, try to stimulate

• Block K⁺ channels: Set K⁺ permeability to 0, observe prolonged spikes

• Disable pumps: Set pump rate to 0, watch gradients decay

• Temperature effects: Change temperature, observe ion movement changes

• Offset experiments: Use offset to simulate different recording conditions

• Multiple stimuli: Create trains of action potentials

🔬 Scientific Accuracy

This simulation uses real neurophysiological parameters:

• Hodgkin-Huxley channel kinetics

• Goldman-Hodgkin-Katz voltage calculations

• Realistic ion concentrations and equilibrium potentials

• Accurate Na⁺/K⁺ pump stoichiometry (3:2 ratio)

• Physiological temperature dependence