Notes on Fiber Types and Their Characteristics

Fiber Type Classification

• Fiber Types: Classified based on their diameter, conduction velocity, myelination, and modality served.

Aa Fibers

• Modality Served: Motor efferent
• Diameter: 12-20 mm
• Conduction Velocity: 70-120 m/s
• Myelinated: Yes

Aα Fibers

• Modality Served: Proprioception
• Diameter: 12-20 mm
• Conduction Velocity: 70-120 m/s
• Myelinated: Yes

Aβ Fibers

• Modality Served: Touch, pressure
• Diameter: 5-12 mm
• Conduction Velocity: 30-70 m/s
• Myelinated: Yes

Aγ Fibers

• Modality Served: Motor efferent (muscle spindle)
• Diameter: 3-6 mm
• Conduction Velocity: 15-30 m/s
• Myelinated: Yes

Aδ Fibers

• Modality Served: Pain
• Diameter: 2-5 mm
• Conduction Velocity: 12-30 m/s
• Myelinated: Yes

Type B Fibers

• Modality Served: Preganglionic autonomic fibers
• Diameter: <3 mm
• Conduction Velocity: Data not specified
• Myelinated: Yes (implied, as they are autonomic fibers)

Type C Fibers

• Modality Served: Pain, Temperature, Touch
• Diameter: 0.3-1.3 mm
• Conduction Velocity: 0.4-1.2 m/s
  • Note: Some type C fibers have a larger diameter up to 3-14 mm, resulting in a conduction velocity of 0.5-2 m/s.
• Myelinated: No, unmyelinated fibers
• Key Characteristics: Slow conduction speed, carrying nociceptive and thermal information.

Summary of Fiber Types

• A Fibers: Myelinated; larger diameter; faster conduction speed; mainly carry motor and sensory information.
• B Fibers: Myelinated; smaller diameter; slower than A fibers; involved in autonomic functions.
• C Fibers: Unmyelinated; small diameter; slow conduction speed; associated with pain and temperature sensations.