Types of Nerve Fibers

According to the size and speed of conduction, the nerve fibers are classified into three different categories, namely A, B and C. These are described in detail below:

Type A fibers:

  1. These fibers are the thickest and fastest conducting.
  2. They are myelinated.
  3. They have a diameter of 1.5-20 micron
  4. Their speed of conduction is 4-120 m/sec, which shows that they have a really fast conduction of impulse.
  5. Examples of type A fibers are skeletomotor fibers, fusimotor fibers and afferent fibers to skin.

Type B fibers:

  1. These fibers are medium in size, i.e. they are smaller than type A fibers but larger than type C.
  2. They are myelinated.
  3. They have a diameter of 1.5-3.5 microns.
  4. Their speed of conduction is 3-15 m/sec, which shows that they are slower than type A fibers.
  5. Examples of type B fibers are preganglionic autonomic efferents.

Type C fibers:

  1. These fibers are the smallest and thinnest.
  2. They are non-myelinated.
  3. They have a diameter of 0.1-2 microns.
  4. Their speed of conduction is 0.5-4 m/sec, which shows that they have the slowest conduction.
  5. Examples of type C fibers are postganglionic autonomic efferents and afferent fibers to skin.