Peripheral Nerve Palsies Flashcards
What is a motor (efferent)
Anterior horn cell (located in the gray matter of the spinal cord)
moto axon
innervates muscles fibres (neuromuscular junction)
What is a sensory unit?
Cell bodies found in posterior root ganglia
Lie outside the spinal cord
What is a peripheral nerve?
The part of the spinal nerve distal to the nerve roots
Bundles of nerve fibres
Range in diameter from 0.3-22 micrometers
Schwann cells form a thin cytoplasmic tube around larger fibres in a multilayered insulating membrane (myelin sheath)
Multiple fibres of connective tissue surrounding the axons
Describe the anatomy of a nerve cell
Axons- long processes of neurones are coated with endoneurium and grouped into
fascicles (nerve bundles) covered with perinerium. These are grouped to form the nerve which is covered with epineurium
Describe the structure of a Aa fibres (1A and 1B fibres)
60-100m/s, large motor axons muscle stretch and tension sensory axons
Describe the structure of a Ab fibres (group II afferent fibres)
30-60 m/s Touch, pressure, vibration and joint position sensory axons
Describe the structure of a Ag fibres
15-30m/s gamma efferent motor axons
Describe the structure of a Ad fibres (group III afferents)
10-15 m/s sharp pain,
Describe the structure of a B fibres
3-10 m/s sympathetic preganglion motor axons
Describe the structure of a C fibres (group IV fibres)
1.5 m/s dullaching, burnign and temperature sensation
What are the classic places where a compression injuries are common?
Carpal tunnel syndrome- median nerve at wrist
Sciatica- spinal root by invertebral disc
Morton’s neurona- digital nerve in 2nd or 3rd web of foot
What is neurapraxia
Nerve in continuity
Stretched (8% will damage microcirculation) or bruise
Reversible conduction block local ischemia or demyelenation
Prognosis is good (weeks or months)
What is axonotmesis
Endonerium intact but disruption of axons
Stretched or crushed by a direct blow
Wallerian dengeneration follows
Prognosis fair, sensory has a better prognosis than motor
What is neurotmesis
Complete nerve division Laceration or avulsion no recovery unless repaired Endoneural tubes disrupted so high chance of miswiring Progognisis poor
What is a closed nerve injury
Associated with nerve injuries in continuity
E.g. neuropraxis, axonotmesis
Spontaneous recovery is possible
Surgery indicatd after 3 months
Axons grow around 1-3mm per day
E.g. brachial plexus injuries, radial nerve humeral fractures
