Axon Diameter and Myelination Determine Nerve Impulse Speed
- Axon Diameter
- Larger axons have less resistance to ion flow, allowing impulses to travel faster.
- Smaller axons have higher resistance, slowing down signal transmission.
- Myelination
- Myelinated fibers are wrapped in a fatty layer called myelin, which insulates the axon and enables saltatory conduction, the jumping of impulses between nodes of Ranvier.
- Non-myelinated fibers lack this insulation, causing impulses to travel more slowly in a continuous wave.
Definition
Myelin
Myelin is a fatty substance that wraps around the axons of neurons, forming an insulating layer.
- Think of myelin as the insulation on electrical wires.
- It prevents signal loss and speeds up transmission.
Comparing Different Types of Nerve Fibers
1. Giant Axons in Squid vs. Smaller Non-Myelinated Fibers
- Giant Axons in Squid
- Diameter: Up to 500 µm.
- Speed: Approximately 25 m/s.
- Function: Rapid escape responses (e.g., jet propulsion).Rapid escape responses (e.g., jet propulsion).
- Smaller Non-Myelinated Fibers
- Diameter: Around 1 µm.
- Speed: About 1 m/s.
- Function: General signal transmission in smaller animals or less urgent responses.
Squid use their giant axons to trigger quick muscle contractions for escape, while smaller fibers handle routine tasks.
2. Myelinated vs. Non-Myelinated Fibers
- Myelinated Fibers
- Speed: Up to 100 m/s.
- Mechanism: Saltatory conduction, where impulses jump between nodes of Ranvier.
- Non-Myelinated Fibers
- Speed: 1–2 m/s.
- Mechanism: Continuous wave-like propagation along the axon.
