Growth Injury and Repair - Peripheral Nerve Injuries Flashcards
Where can you find a motor unit?
Anterior horn cell - located in the gray matter of the spinal cord
Motor axon
Muscle fibres
Where do you find a sensory unit?
Cell bodies are in the posterior root ganglia (outised the spinal cord)
Which is anterior/posterior
Motor roots
Sensory roots
•Nerve fibres join to form
–anterior (ventral) motor roots
–posterior (dorsal) sensory roots
Where do spinal nerves exit the vertebral column?
Exit the vertebral column via an intervertebral foramen
What is defined as a peripheral nerve?
•The part of a spinal nerve distal to the nerve roots.
What are the three functional units of nerves?
AXONS (long processes of neurones) are coated with endoneurium and grouped into
FASCICLES (nerve bundles ) covered with perineurium; these are grouped to form the
NERVE which is covered with epineurium
What type of cell surrounds nerve cells?
Schwann cells
What type of information do A alpha fibres carry?
They carry large motor axons and muscle stretch and tension sensory axons
What do A beta fibres carry?
Touch pressure vibration and joint position
What do A gamma fibres carry?
Gamme afferent motor axons
What do A delta fibres carry?
Sharp pain, very light touch and temperature sensation
What type of information does B fibres carry?
Sympathetic preganglionic motor axons
What type of information does group C fibres carry?
Dull, aching, burning pain and temperature sensation
What type of injury is possible for nerves?
Compression or trauma
What are the different type of traumas to the nerve?
Direct (blow or laceration)
Indirect (avulsion, traction)
–neurapraxia (loss of nerve function due to blockage of nerve conduction)
–axonotmesis (axons and meyelin sheath are damaged however, the endoneurium, perineurium and the epineurium remain intact)
–neurotmesis (both nerve and nerve sheath are disrupted)
Give examples of common compression injuries of nerves?
Carpal tunnel syndrome - median nerve in the wrist
Sciatica - spinal root by intervertebral disc
Mortons neuroma - digital nerve in the 2nd or 3rd web space of forefoot
What is neurapraxia?
–nerve in continuity
–stretched (8% will damage microcirculation) or bruised
–reversible conduction block - local ischaemia and demyelination
–prognosis good (weeks or months)
(so there is local ischaemia and demyelination but the continuity of the nerve is still intact)
What is axonotemesis?
–endoneurium intact (tube in continuity), but disruption of axons; more severe injury
–stretched ++ (15% elongation disrupts axons) or crushed or direct blow
–Wallerian degeneration follows
–prognosis fair (sensory recovery often better than motor - often not normal but enough to recognise pain, hot & cold, sharp & blunt)
What is wallerian degeneration?
Wallerian degeneration is a process that results when a nerve fiber is cut or crushed and the part of the axon distal to the injury (i.e. farther from the neuron’s cell body) degenerates.
What is neurotemesis?
–complete nerve division
–laceration or avulsion
–no recovery unless repaired (by direct suturing or grafting)
–endoneural tubes disrupted so high chance of “miswiring” during regeneration
–prognosis poor
Summary
What is meant by a closed nerve injury?
•Associated with nerve injuries in continuity
–neuropraxis
–axonotmesis,
- spontaneous recovery is possible
- surgery indicated after 3 months
– if no recovery is identified
- Clinical
- Electromyography
- axonal growth rate (1–3 mm/day)
Can you give examples of closed nerve injuries
Typically stretching of the nerve
Brachial plexus injuries
Radial nerve - humeral fracture. A fracture in the shaft of the humerus can result in entrapment of the radial nerve in the spiral groove - clinically this is seen as a wrist drop
What are open nerve injuries?
•Frequently related to nerve division
– neurotmetic injuries
–E.g. knives /glass
- Treated with early surgery
- Distal portion of the nerve undergoes Wallerian degeneration
–Occurs up 2 to 3 weeks after the injury.
