Primary afferent groups

  Muscle nerve Cutaneous nerve Fiber diameter (mm) Conduction velocity (m/s)

Myelinated

Large

Medium

Small

 

I

II

III

 

Aa

Ab

Ad

 

12-20

6-12

1-6

 

72-120

36-72

4-36

Unmyelinated IV C 0.2-1.5 0.4-2.0

Primary afferent fibers

Modality Submodality Receptor Fiber Perception
Mechanoreception

SAI

RA

SAII

PC

Merkel cell

Meissner corpuscle

Ruffini corpuscle

Pacinian corpuscle

Ab

Ab

Ab

Ab

Pressure, Form, Texture

Flutter, Motion

?

Vibration

Thermoreception

Warm

Cold

Bare nerve ending

C

Ad

Warmth

Cold

Nociception

Small, myelinated

Unmyelinated

Bare nerve ending

Ad

C

Sharp pain

Burning pain

Proprioception

Joint afferents

Golgi tendon organs

Muscle spindles

SAII

diverse

Golgi endings

Type I

Type II

Ruffini endings

Aa

Aa

Aa

Ab

Ab

Protective function

Muscle tension

Muscle length & velocity

Muscle length

?