Fiber category

Size (microns)

Speed (meters/second)

Function

Aa

Group IA and IB afferents

15

60-100

Large motor axons Muscle stretch and tension sensory axons

Ab

Group II afferents

12-14

30-60

Touch, pressure, vibration and joint position sensory axons

Ag

8-10

15-30

Gamma efferent motor axons

Ad

Group III afferents

6-8

10-15

Sharp pain, very light touch & temperature sensation

B

2-5

3-10

Sympathetic preganglionic motor axons

C

Group IV afferents

<1

<1.5

Dull, aching, burning pain and temperature sensation