Learning Objective
By the end of this section, the learner should be able to explain the factors affecting conduction velocity in neurons, describe the role of cell diameter and myelination, and understand how saltatory conduction enhances action potential propagation.
Factors Affecting Conduction Velocity
1. Cell Diameter
- Principle: Larger diameter axons conduct action potentials faster.
- Mechanism: Greater cross-sectional area → lower internal electrical resistance → faster current flow along the axon.
- Clinical correlation: Large-diameter myelinated fibers (e.g., motor neurons) transmit impulses faster than small-diameter sensory fibers (e.g., pain fibers).
2. Myelination
- Principle: Myelin increases conduction velocity.
- Mechanism:
- Myelin insulates the membrane, reducing current leakage.
- Nodes of Ranvier are unmyelinated gaps where fast Na⁺ channels cluster.
- Action potentials “jump” from node to node, a process called saltatory conduction.
- Result: Faster propagation with minimal loss of signal.
Activity
Key Points
- Larger axon diameter → faster conduction.
- Myelination → faster, energy-efficient conduction via saltatory mechanism.
- Nodes of Ranvier are essential for the regeneration of action potentials.
- These principles apply to all synapses for effective neurotransmission.
