Saltatory Conduction

Created in September 01, 2025

2025   ·   neuroscience   myelin   axon   conduction

Saltatory conduction is a mechanism of nerve impulse propagation in myelinated axons, where the action potential “jumps” from one node of Ranvier to the next, rather than traveling continuously along the axon. This process significantly increases the speed and efficiency of neural transmission.

Key Components:

  • Myelin Sheath: A fatty, insulating layer produced by Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system. It wraps around the axon, leaving small gaps called nodes of Ranvier.
  • Nodes of Ranvier: Unmyelinated gaps rich in voltage-gated ion channels (e.g., sodium and potassium channels), essential for regenerating the action potential.

Mechanism:

  1. Ion Flow Restriction: Myelin prevents ion leakage across the axon membrane, reducing capacitive current and allowing the depolarizing signal to spread farther with less attenuation.
  2. Signal “Jumping”: The action potential depolarizes one node of Ranvier, triggering voltage-gated sodium channels to open and influx Na⁺ ions. This depolarization passively spreads through the myelinated internode to the next node, where it reaches threshold and regenerates the action potential. Thus, the impulse appears to “jump” between nodes.
  3. Energy Efficiency: Since ion exchange only occurs at the nodes, less ATP is required to restore ionic gradients via the sodium-potassium pump (Na⁺/K⁺-ATPase) compared to unmyelinated axons.

Advantages:

  • Increased Conduction Velocity: Saltatory conduction can achieve speeds up to 100 m/s, whereas unmyelinated axons typically conduct at 0.5–2 m/s.
  • Reduced Metabolic Cost: Limited ion channel activity conserves energy.

Mathematically, the conduction velocity \(v\) in myelinated axons can be approximated by \(v \propto \frac{d}{\tau}\), where \(d\) is the axon diameter and \(\tau\) is the time constant, but saltation optimizes this further by leveraging internodal distance and myelin thickness.

This process is critical for rapid response in neural systems, such as reflex arcs and motor coordination.