Nerve Fiber Classification
- Core Principle: Conduction Speed ∝ Diameter & Myelination.
- A-α fibers
- Structure: Largest diameter, most myelinated. Fastest.
- Function: Proprioception (muscle spindles, Golgi tendons) & somatic motor (α-motor neurons).
- A-β fibers
- Structure: Large, myelinated. Fast.
- Function: Fine touch, vibration, pressure.
- A-δ fibers
- Structure: Small, thinly myelinated. Slower.
- Function: Fast, sharp pain & cold temperature.
- B fibers
- Structure: Lightly myelinated.
- Function: Preganglionic autonomic fibers.
- C fibers
- Structure: Smallest diameter, unmyelinated. Slowest.
- Function: Slow, dull, burning pain, warmth, & postganglionic autonomic fibers.
Clinical Correlations
- Speed of Sensation: Touch/Pressure (A-β) > Sharp Pain (A-δ) > Dull/Aching Pain (C).
- Susceptibility to Blockade:
- Pressure/Ischemia: Large fibers are most sensitive (A > B > C). Leads to numbness first.
- Local Anesthetics: Small fibers are most sensitive (C > B > A). Blocks pain first.