Capacitance and Myelination vs.

Conduction Velocity

Mengqi Xing, Basheer Subei, Rafael Romero

Membrane Thickness

• Soliton Model of Action Potentials– Soliton (mechanical wave) propagates

along membrane that causes AP– Thermodynamically sound– Δ in membrane thickness = Δ in

Capacitance• Piezoelectricity

𝐶=ε r ε 0𝐴𝑑

Myelin Distribution• Myelin sheaths– Δ membrane thickness Δ membrane

capacitance – Speed up AP propagation

• Distribution of Myelin– Nodes of Ranvier• Hodgkin-Huxley Model

–Myelination• Passive Cable Model

Methods• Testing Spatial Distribution of Myelin:– 6 Different Distributions– Control, Full, Short, Long, Mid Gap,

Multiple Gap– Scaled up axon dimensions

• Studying:– Effect of Membrane Thickness/Distribution– Significance of Nodes of Ranvier– Conductance velocity

Different Distributions

Control

Short Myelin

Full

Long Myelin

Mid Gap Multiple Gap

Control

Full Myelin

Short Myelin

Long Myelin

Mid Gap Myelin

Multiple Gap

Average Conduction Velocity

Control Multiple Gap Mid Gap Full0

1000

2000

3000

4000

5000

6000

7000

2 mA Current

Myelin Distribution

Aver

age

Velo

city

(m/s

)

Control Multiple Gap Mid Gap FullVelocity (m/s) 191.36 438.55 620.4 6049

Discussion• Main Points:–Myelination • Fast conduction BUT AP decays• No gates ∴ no current to recharge AP

– No myelination • Signal Slow• Gates throughout axon allow propagation

• Nodes of Ranvier– Recharge AP & prevent signal decay

Thanks!