Discussion Overview
The discussion centers around the role of myelin in increasing resistance and decreasing capacitance across the cell membrane, particularly in relation to the speed of action potentials in myelinated versus demyelinated axons. Participants explore the implications of these changes on signal velocity and the underlying mechanisms involved, including the structure of neurons and the behavior of capacitors in series.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
- Mathematical reasoning
Main Points Raised
- Some participants reference Wikipedia's claim that myelin increases resistance by a factor of 5,000 and decreases capacitance by a factor of 50, questioning the reasoning behind the decrease in capacitance.
- One participant suggests that myelin may increase the distance between capacitor plates more than it changes the dielectric constant, affecting capacitance.
- Another participant provides experimental data indicating that action potentials travel at approximately 25 m/s in unmyelinated axons and can increase to about 50 m/s in myelinated axons.
- It is noted that myelin reduces capacitance because the multiple layers of myelin around a neuron act like capacitors in series, leading to a decrease in total capacitance.
- Some participants discuss the implications of demyelination, suggesting that it could prevent action potentials from propagating effectively due to a lack of voltage-gated channels beneath the myelin sheath.
- There is a suggestion that the depolarization at nodes of Ranvier may be greater in demyelinated axons compared to myelinated axons, raising questions about the dynamics of action potential generation.
- One participant emphasizes that while myelin increases resistance and decreases capacitance, action potentials will still decay over time and need to be regenerated at the nodes of Ranvier.
Areas of Agreement / Disagreement
Participants express various viewpoints on the effects of myelin on capacitance and action potential propagation, with no clear consensus reached. Some agree on the basic principles of how myelin affects conduction velocity, while others raise questions about the specifics of demyelination and its consequences.
Contextual Notes
Participants acknowledge that the discussion involves complex interactions between capacitance, resistance, and the structure of neuronal membranes, with some limitations in the assumptions made about the behavior of demyelinated axons and the presence of voltage-gated channels.
