Peripheral Nerve Injuries

• Neurone:

  • is a nerve cell
  • it is electrically excitable and communicates with other cells via specialised connections called synapses
  • neurones receive impulses from other cells via the dendrites, and then it travels down the nerve, through the axon, and then the impulse leaves via the axon terminals
  • the cell nucleus plays an important role in nerve regeneration

  A) dendrites

  B) nucleus

  C) body

  D) myelin sheath

  E) Schwann cell

  F) Nodes of Ranvier

  G) axon terminal

  
• Neurone:

  • Schwann cells myelinate the axon of the peripheral nerve system
  • myelin is a fatty layer, it insulates the axon and it helps increase the ability of nerve conduction
  • some nerves are myelinated (faster), some nerves are non-myelinated (slower)
  • Nodes of Ranvier are gaps in between the Schwann cells
  • smaller Schwann cells = more Nodes of Ranvier = slower speed of conduction as there's smaller hops
  • bigger Schwann cells = less Nodes of Ranvier = faster speed of conduction as there's bigger hops

  
• Nerve Structure:

  • a neuron is represented as labels A (axon) and B (myelin sheath) in this diagram of a whole nerve
  • endoneurium - connective tissue that surrounds each neuron
  • epineurium - connective tissue that surrounds each nerve
  • fascicle - a group of axons
  • perineurium - connective tissue that surrounds each fascicle
  • blood vessel in the nerve - supplied by very small nerves called nervi nervorum

  A) axon

  B) myelin sheath

  C) endoneurium

  D) epineurium

  E) fascicle

  F) perineurium

  G) blood vessels

  
• Signs & Symptoms of Nerve Injury:

  • loss of reflexes (peripheral nerve initiate reflexes)
  • loss of voluntary control, leads to
  • muscle atrophy, leads to
  • deformity (different nerves have different deformities associated with their damage), leads to
  • oedema
• Surgical Repair - common after neurotmesis:

  • neurolysis - removal of scar tissue around the nerve to help it move better
  • autografting - used for severed nerves - sensory nerve from a different part of the body is used to fill the gap of the damaged nerve (using a motor nerve will impair pts function)
  • redirect nerve via short route - sometimes nerves sit in vulnerable positions, changing its location can make it less likely to be compressed
• Take Home Message:

  • Prognosis dependent on degree of nerve damage
  • Recovery can be very SLOW
  • Many different symptoms associated with nerve injury
  • Knowledge of sensory and motor supply essential to assist with diagnosis of likely level of nerve injury