Nerve fibre classification and clinical correlates (large myelinated vs small unmyelinated)
Core concept
- Erlanger-Gasser (A / B / C, all nerves) with the Lloyd sensory numbering (I-IV) in brackets
| Fibre | Myelin, diameter | Speed | Function |
|---|---|---|---|
| A-alpha (Ia, Ib) | Heavy, 13-20 um | 70-120 m/s | Alpha motor; muscle spindle Ia, Golgi tendon Ib -> proprioception |
| A-beta (II) | Heavy, 6-12 um | 30-70 | Vibration, light touch, proprioception |
| A-gamma | 3-6 um | 15-30 | Intrafusal (spindle) motor |
| A-delta (III) | Thin, 1-5 um | 5-30 | Fast sharp pain, cold |
| B | Lightly myelinated, <3 um | 3-15 | Preganglionic autonomic |
| C (IV) | Unmyelinated, 0.2-1.5 um | 0.5-2 | Slow burning pain, warmth, itch, postganglionic autonomic |
- The clinical split that matters
- Large myelinated -> vibration, joint position, light touch, reflexes, power
- Small (A-delta + C) -> pain, temperature, autonomic
3 more sections, plus exam facts
Premium unlocks every note across every specialty, and the full exam fact library behind it.
Get premium access