PNS Pathology

Question 1

What makes up the PNS?

Answer 1

Nerves, ganglia, neuronal cells bodies, nerve endings

Question 2

What are the roles of ascending and descending tracts?

Answer 2

Ascending tracts carry sensory information to the CNS, descending tracts are responsible for motor movement

Question 3

What are four types of nerve injuries?

Answer 3

Neurapraxia, axonal degeneration, axonotmesis, neurotmesis

Question 4

What is neurapraxia?

Answer 4

Injury to myelinated nerve by pressure that interrupts conduction, causing temporary paralysis and loss of function with no degeneration and complete, rapid recovery

Question 5

What can cause neurapraxia?

Answer 5

Trauma to the body, eg. hard blow to head, shoulder, or back, common in contact sports

Question 6

What is axonal degeneration?

Answer 6

Direct injury to axon leading to axon transection/crushing resulting in Wallerian degeneration

Question 7

Describe Wallerian degeneration

Answer 7

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

Question 8

Describe the conditions for regeneration in PNS nerves.

Answer 8

If soma damaged, no regeneration. If axon damaged, cell can regenerate.

Question 9

What is acute axonal injury?

Answer 9

Nerve atrophy, resulting in decreases density of axons, which reduces amplitude strength of nerve impulses

Question 10

What is acute demyelinating disease?

Answer 10

Segmental degeneration with axon sparing, resulting in slow nerve conduction

Question 11

What is axonotmesis?

Answer 11

Nerve injury in which axons and myelin sheaths are damaged but endoneurium, perneurium, and epineurium remain intact

Question 12

What can cause axonotmesis?

Answer 12

Stretch injury, i.e. limb fractures and dislocations sever peripheral nerves

Question 13

What is the outcome of axonotmesis?

Answer 13

Wallerian degeneration, followed by regeneration and functional recovery

Question 14

What is neurotmesis?

Answer 14

Complete severance or crushing of nerve

Question 15

What is the outcome of neurotmesis?

Answer 15

Distal Wallerian degeneration, recovery not expected

Question 16

What are peripheral neuropathies?

Answer 16

Heterogenous group of diseases resulting from inflammatory, toxic and metabolic conditions in addition to genetic defects

Question 17

What symptoms may present in a peripheral neuropathy?

Answer 17

Movement impairment, sensory impairment, autonomic nerve impairment (control of organs)

Question 18

What are some example of peripheral neuropathies?

Answer 18

Trauma (car accidents, sports injuries), diabetic neuropathy, chemotherapy induced neuropathy, viral neuropathy, autoimmune, genetic

Question 19

What are the six primary mechanisms causing neuropathies?

Answer 19

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

Question 20

What is Guillian-Barre syndrome?

Answer 20

Autoimmune diseased in which the myelin or axons are targeted by antibodies and lymphocytes (acute)

Question 21

How common is Guillian-Barre syndrome?

Answer 21

Rare, 1-2 in 100,000

Question 22

What caused Guillian-Barr syndrome?

Answer 22

Unknown cause, usually follows viral or bacterial infection (EBV, CMV, HIV, C. jejuni)

Question 23

Why can Guillian-Barre syndrome be life-threatening?

Answer 23

During acute phase, 15% develop weakness of breathing muscles

Question 24

Describe the progression of Guillian-Barre syndrome.

Answer 24

Sudden onset followed by rapid progression and slow resolution as nerves heal

Question 25

What is Charcot-Marie-Tooth disease (1A)?

Answer 25

Genetic neuropathy caused by duplication, mutation in gene coding peripheral myelin protein PM22 (chronic and hereditary)

Question 26

How common is Charcot-Marie-Tooth disease?

Answer 26

1 in 2500 people affected

Question 27

What are symptoms of Charcot-Marie-Tooth disease?

Answer 27

Motor and sensory abnormalities - muscle weakness and pain, decreased reflexes, difficulty heel walking, calf atrophy, high arch and hammer toe

Question 28

Describe the progression of Charcot-Marie-Tooth disease.

Answer 28

Subtle onset of symptoms with slow progression. Follows relapsing-remitting or progressive course. May worsen over time