PNS Pathology Flashcards
What makes up the PNS?
Nerves, ganglia, neuronal cells bodies, nerve endings
What are the roles of ascending and descending tracts?
Ascending tracts carry sensory information to the CNS, descending tracts are responsible for motor movement
What are four types of nerve injuries?
Neurapraxia, axonal degeneration, axonotmesis, neurotmesis
What is neurapraxia?
Injury to myelinated nerve by pressure that interrupts conduction, causing temporary paralysis and loss of function with no degeneration and complete, rapid recovery
What can cause neurapraxia?
Trauma to the body, eg. hard blow to head, shoulder, or back, common in contact sports
What is axonal degeneration?
Direct injury to axon leading to axon transection/crushing resulting in Wallerian degeneration
Describe Wallerian degeneration
Injury leading to axotomy, destruction of axon and myelin, macrophages and Schwann cells remove cell debris, connection to target muscle lost (atrophy and fibrosis of muscle), macrophages release mitogens that stimulate Schwann cell division, Schwann cells align with Büngner bands and express surface molecules that guide regenerating fibres, axons sprout and reconnects, remyelination
Describe the conditions for regeneration in PNS nerves.
If soma damaged, no regeneration. If axon damaged, cell can regenerate.
What is acute axonal injury?
Nerve atrophy, resulting in decreases density of axons, which reduces amplitude strength of nerve impulses
What is acute demyelinating disease?
Segmental degeneration with axon sparing, resulting in slow nerve conduction
What is axonotmesis?
Nerve injury in which axons and myelin sheaths are damaged but endoneurium, perneurium, and epineurium remain intact
What can cause axonotmesis?
Stretch injury, i.e. limb fractures and dislocations sever peripheral nerves
What is the outcome of axonotmesis?
Wallerian degeneration, followed by regeneration and functional recovery
What is neurotmesis?
Complete severance or crushing of nerve
What is the outcome of neurotmesis?
Distal Wallerian degeneration, recovery not expected
What are peripheral neuropathies?
Heterogenous group of diseases resulting from inflammatory, toxic and metabolic conditions in addition to genetic defects
What symptoms may present in a peripheral neuropathy?
Movement impairment, sensory impairment, autonomic nerve impairment (control of organs)
What are some example of peripheral neuropathies?
Trauma (car accidents, sports injuries), diabetic neuropathy, chemotherapy induced neuropathy, viral neuropathy, autoimmune, genetic
What are the six primary mechanisms causing neuropathies?
1. Altered metabolism
2. Covalent modification
3. Altered organelle function and reactive oxygen species formation
4. Altered intracellular and inflammatory signalling
5. Slowed axonal transport
6. Altered ion channel dynamics and expression
What is Guillian-Barre syndrome?
Autoimmune diseased in which the myelin or axons are targeted by antibodies and lymphocytes (acute)
How common is Guillian-Barre syndrome?
Rare, 1-2 in 100,000
What caused Guillian-Barr syndrome?
Unknown cause, usually follows viral or bacterial infection (EBV, CMV, HIV, C. jejuni)
Why can Guillian-Barre syndrome be life-threatening?
During acute phase, 15% develop weakness of breathing muscles
Describe the progression of Guillian-Barre syndrome.
Sudden onset followed by rapid progression and slow resolution as nerves heal
What is Charcot-Marie-Tooth disease (1A)?
Genetic neuropathy caused by duplication, mutation in gene coding peripheral myelin protein PM22 (chronic and hereditary)
How common is Charcot-Marie-Tooth disease?
1 in 2500 people affected
What are symptoms of Charcot-Marie-Tooth disease?
Motor and sensory abnormalities - muscle weakness and pain, decreased reflexes, difficulty heel walking, calf atrophy, high arch and hammer toe
Describe the progression of Charcot-Marie-Tooth disease.
Subtle onset of symptoms with slow progression. Follows relapsing-remitting or progressive course. May worsen over time
