Where can you find a motor unit?
Anterior horn cell - located in the gray matter of the spinal cord
Where do you find a sensory unit?
Cell bodies are in the posterior root ganglia (outised the spinal cord)
Which is anterior/posterior
•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?
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
What is meant by a closed nerve injury?
•Associated with nerve injuries in continuity
- spontaneous recovery is possible
- surgery indicated after 3 months
– if no recovery is identified
- 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.
What are the features of sensory loss due to nerve injury?
–dysaethesiae (disordered sensation)
•anaesthetic (numb), hypo- & hyper-aesthetic, paraesthetic (pins & needles)
What are the features of motor loss due to nerve injury?
Paresis (weakness) or paralysis with or without wasting
Dry skin - because the patient can’t sweat, loss of tactile adherence since sudomotor nerve fibres not stimulating sweat glands in the skin
How can reflexes be altered as a result of nerve injury?
Reflexes may be diminished or absent
How do nerves heal?
- very slow!!
- starts with initial death of axons distal to site of injury
–Then degradation myelin sheath
- proximal axonal budding occurs after about 4 days
- regeneration proceeds at rate of about 1 mm/day (or 1 inch/month) - poss. 3-5 mm/day in children
- pain is first modality to return
What factors affect the rate of healing of a nerve?
Prognosis for recovery depends
•whether nerve is
–“pure” (only sensory or only motor)
–“mixed” (both sensory and motor within same nerve)
•how distal the lesion is (proximal worse)
What sign can be used to monitor nerve healing?
•Tinel’s sign can monitor recovery
– (tap over site of nerve and paraesthesia will be felt as far distally as regeneration has progressed)
How can injury be assessed and recovery be monitored for nerve injuries?
•Injury can be assessed, and recovery monitored
–by electrophysiological Nerve Conduction Studies
What types of nerve repair exist?
–No loss nerve tissue
- Sural nerve (sural nerve is a pure cutaneous nerve. The sural nerve innervates lateral & posterior third of leg and lateral aspect of foot & heel, & lateral portion of the ankle. The sural nerve grafts are frequently used as cablegrafts.
What is the rule of three?
Surgical timing in a traumatic peripheral nerve injury
- Immediate surgery within 3 days for clean and sharp injuries
- Early surgery within 3 weeks for blunt/contusion injuries
- Delayed surgery, performed 3 months after injury, for closed injuries.
What are the differences between peripheral or central nerve injuries?