Transmission / Fibre classes
Classification of somatosensory nerve fibres
| Somatosensory nerve fibres can be divided into several subcategories based on their conduction velocity (which is determined by their diameter and degree of myelination). This classification system is important for understanding pain and the mechanism of action of local anaesthetics. |  |
 |
Fibre Type |
Axon Diameter (microns) |
Conduction Velocity (m/s) |
Modalities |
| Myelinated Fibres | ||||
Aβ |
14.0 |
25 |
mechanoreception |
|
Aδ |
11.0 |
17 |
mechanoreception, cold, fast pain |
|
| Unmyelinated Fibres | ||||
C |
2.5 |
0.4-0.5 |
mechanoreception, thermoreception, slow pain |
|
* for reference, B fibres ---- myelinated fibres found in autonomic nerves that are the same diameter as C fibres --- conduct at least 10X faster (3-15 m/s) than C fibres
- conduction velocity explains the timing differences among the modalities you experience when you stub your toe:
- "I hit my toe. [mechanoreception carried by Aβ fibres]. Ow! [fast pain carried by Aδ fibres]"