Peripheral axons

An axon is responsible for the conduction of action potentials along its length to communicate between the central nervous system and the periphery. Afferent nerve fibres transmit signals from receptors in the periphery towards the nerve cell body. Nerve fibres are classified into Groups of A, B and C fibres. A and B type fibres are myelinated and C fibres are unmyelinated. Alternatively, a classification exists of sensory fibres only of Type I, II, III, IV (Figure 1). Conduction speed relates to the degree of myelination and axon diameter.
Figure 1
  • AAlpha fibres include type Ia and b fibres and refer to afferent fibres from skeletal muscle i.e golgi tendon organs and muscle spindles
  • ABeta and Agamma fibres are Type II fibres and are afferent fibres from stretch receptors
  • ADelta fibres are Type III fibres and are nociception fibres relating to acute pain, cold and pressure
  • B fibres are less myelinated than A fibres and are usually general visceral afferent fibres and preganglionic nerve fibres of the autonomic nervous system
  • C fibres are unmyelinated and have a small diameter and low conduction velocity. They are polymodal because they can react to temperature, mechanical or chemical stimulus. C fibres convey temperature, itch, pain


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