3D Action Potential - Myelinated vs Unmyelinated

🔬 Electrode Reading

-70mV

Resting State

Ready to Fire

⚡ Na⁺/K⁺-ATPase: Standby

AP Waveform at Electrode

-100 ms t=0 @ AP arrival 500 ms

📊 Hillock Voltage (Long Scale)

0 Threshold: -55mV 5s

Membrane / Cytoplasm

Na⁺ (extracellular → influx)

K⁺ (intracellular → efflux)

Cl⁻ (IPSP / inhibitory)

Refractory (channels inactivated)

NT vesicles & release

Ca²⁺ (extracellular)

Myelinated Neuron (Bottom):

Myelin sheath (insulating)

Node of Ranvier (channels)

⚡ Saltatory vs Continuous Conduction

Unmyelinated (continuous)

Myelinated (saltatory)

Unmyelinated

-- ms

Myelinated

-- ms

Speed Ratio: --x faster

Why myelination speeds conduction:
• AP "jumps" between nodes (saltatory)
• No ion exchange under myelin
• Reduced capacitance → faster charging
• ~6x faster in myelinated axons

Animation Controls

Loop Animation

🧠 Comparison Mode

Show Myelinated Neuron

Adds a second neuron below with myelin sheaths to compare saltatory vs continuous conduction

Animation Speed 1.0x

Synaptic Input

Spontaneous EPSP Rate 50%

Spontaneous IPSP Rate 30%

Extracellular Ion Visibility

Show Extracellular Ions

Hide Na⁺/Cl⁻/Ca²⁺ in extracellular space to save GPU memory

Na⁺ (extracellular) 50%

K⁺ (intracellular) 35%

Cl⁻ (extracellular) 40%

Ca²⁺ (extracellular) 45%

Neuron Properties

Na⁺ Channel Density 100

K⁺ Channel Density 100

Propagation Speed 100

Transit (1.5mm): -- unmyel | -- myel

Real: 0.75ms (1μm) | 0.013ms (20μm)

Synaptic Integration:
• EPSPs (red glow) depolarize dendrites
• IPSPs (blue glow) hyperpolarize
• Soma integrates spatially & temporally
• Threshold at hillock: -55 mV → AP!
• Dark regions = refractory period

Ion Flow During AP:
• 🔴 Red = Na⁺ (rushes IN during depol.)
• 🟡 Yellow = K⁺ (rushes OUT during repol.)
• 🔵 Blue = Cl⁻ (IPSPs)

Na⁺/K⁺-ATPase Pump:
• 3 Na⁺ pumped OUT : 2 K⁺ pumped IN
• Restores resting concentrations

FPS: 60

Soma V: -70 mV

Hillock V: -68 mV

[Na⁺]ᵢ: 15.4 mM

Hillock +ions: 0

Active Ions: 0

Wave Position: 0%