connective tissue

Last reviewed 01/2018

The connective tissue of the peripheral nervous system makes up to three quarters of the cross section of a peripheral nerve. It is composed of several discrete layers encapsulating neurones, glial cells and blood vessels:

• endoneurium:
  • a loose, collagenous matrix containing fibroblasts and ground substance
  • surrounds individual axons within a fascicle
  • axon size within fascicular unit varies from 0.2 micrometres (unmyelinated) to 25 micrometres (myelinated)
• perineurium:
  • surrounds a group of nerve fibres as a fascicle
  • acts as a bi-directional barrier to diffusion
  • composed of up to ten layers of mesothelial type cells that are interlinked by tight junctions
  • a strong, elastic layer
  • fascicular size can be up to 3 mm in larger nerves
• epineurium:
  • the outer layer of a peripheral nerve that provides a supportive and protective barrier
  • divided into an:
    • external epineurium surrounding the whole nerve as an outer sheath
    • internal epineurium composed of looser connective tissue that contains a longitudinal plexus of blood vessels
  • usually the layer that is stitched during nerve repairs