Peripheral nerve injuries Flashcards
The motor unit?
Motor unit (efferent):
> Anterior horn cell, (located in the gray matter of the spinal cord)
> Motor axon,
> Muscle fibres (neuromuscular junctions)
Sensory unit?
Sensory unit:
> cell bodies in posterior root ganglia
> I.e. lie outside the spinal cord
What do nerve fibres join to form?
Nerve fibres join to form:
> anterior (ventral) motor roots
> posterior (dorsal) sensory roots
Spinal nerves?
Spinal Nerves
> Anterior and posterior roots combine to form a spinal nerve.
> Exit the vertebral column via an intervertebral foramen.
Anterior/ventral nerve fibres?
Motor
Posterior/dorsal nerve fibres?
Sensory
What is considered a peripheral nerve?
Nerves distal to spinal nerve roots
What is the diameter of peripheral nerves?
Range in diameter from 0.3-22um
What are peripheral nerves?
A peripheral nerve is a highly organised structure comprised of nerve fibres, blood vessels and connective tissue
What are axons?
AXONS = Long processes of neurones
What are axons covered in?
Endoneurium
What are fascicles?
Nerve bundles
What are fascicles covered in?
Perineurium
What is a nerve covered in?
Epineurium
What are neurones surrounded by?
Schwann cells
Role of Aα, Group IA and IB afferents nerve fibres?
> Large motor axons
> Muscle stretch and tension sensory axons
Role of Aβ, Group II afferents nerve fibres?
Touch, pressure, vibration and joint position sensory axons
Role of Aγ nerve fibres?
Gamma efferent motor axons
Role of Aδ, Group III afferents
nerve fibres?
Sharp pain, very light touch & temperature sensation
Role of group B fibres?
Sympathetic preganglionic motor axons
Role of Group C, Group IV afferents nerve fibres?
Dull, aching, burning pain and temperature sensation
Types of injury to peripheral nerves?
> Compression - “Nerve palsies in the limbs” ]
> Trauma - direct (blow, laceration) or indirect (avulsion, traction)
- Neurapraxia
- Axonotmesis
- Neurotmesis
> Entrapment
Examples of classical conditions with peripheral nerve entrapment?
> Carpal tunnel syndrome
Median nerve at wrist
> Sciatica
Spinal root by intervertebral disc
> Morton’s neuroma
(digital nerve in 2nd or 3rd web space of forefoot)
What is neuropraxia?
NEURAPRAXIA -
> nerve in continuity
> stretched (8% will damage microcirculation) or bruised
> reversible conduction block - local ischaemia and demyelination
> prognosis good (weeks or months)