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The Peripheral Nerve Fiber Types

The nervous system is a very complex arrangement of nerve fibers into what we recognize as nerves.  In that nervous system, we have the central nervous system made up of the brain and spinal column and the peripheral nerves consisting of the nerves extending from the spinal column.   In these peripheral nerves, the individual nerve fibers are organized into groups (called fascicles).  Each fascicle is surrounded by connective tissue (called the perineurium).   Larger nerve fibers include a myelin sheath or endoneurium that allows more rapid transport of signals.  In smaller nerve fibers, the myelin sheath is not required.   In either case, multiple fascicles can then be grouped together with a blood supply and fatty tissue into an epineurium.  

Anatomy of a Nerve
© Alila07 | Dreamstime.com - Anatomy Of A Nerve Photo

The fascicles are made up of different nerve types which are classified by size and function.   The smaller nerves are also found to have slower signal velocities that can be influenced by malfunctioning nerves.  The nerve fiber classification is as follows:

Classification Fiber Type Diameter
(microns)
Functions
A-alpha Large Fiber 10-20
  • Motor:  Alpha motoneurons
  • Sensory:  Spindle afferents (Stretch Reflexes)
    Golgi Afferents (Tendon Protection Reflex)
    Touch
    Pressure
       
A-beta Large Fiber 5-12
  • Sensory:  Spindle afferents (Stretch Reflexes)
    Touch
    Pressure
    Vibration
       
A-gamma Large Fiber 2-8
  • Motor:  Gamma motoneurons
       
A-delta Large Fiber 1-5
  • Sensory: Touch
    Pain
    Temperature
       
B Large Fiber 1-3
  • Autonomic Nervous System
       
C (unmyelinated) Small Fiber 1
  • Sensory:  Pain
    Temperature
  • Autonomic Nervous System

 

Brandt R Gibson, DPM
Podiatrist, Neuropathy Doctor, Father of 11 and Founder of Mountain West Foot & Ankle Institute