Peripheral Nerves and Injury

Question 1

In a typical peripheral nerve, what type of cell generates collagen fibres?

Answer 1

Fibroblasts.

Question 2

True of false: oligodendrocytes myelinate PNS axons.

Answer 2

False. They myelinate CNS axons. Schwann Cells are used in the PNS.

Question 3

There are two types of classification methods for never fibres: physiological and anatomical. How are fibres physiologically distinguished from one another? Describe the different groups.

Answer 3

Nerve conduction times are measured. Different fibre diameters (and myelinated vs unmyelinated) have different transmission velocities.

There are 3 main types:
I) Group A, myelinated sensory and motor (alpha, beta, gamma and delta)
II) Group B, slower and thinly myelinated (pre gang, autonomic)
III) Group C, unmyelinated

Used for efferents (A-alpha) and small pain .

Question 4

Describe the anatomical system of nerve fibre type.

Answer 4

There are 4 groups based on diameter.
I, II, III (myelinated), IV (unmyelinated).

Used for or myelinated afferents (Ia from primary MS afferents, Ib from GTO, II secondary endings from MS and from some receptors of skin and joints).

Question 5

Epineurium surrounds PN fibres (up to 35% of thickness in sciatic n.) for protection. What is it primarily composed of and what does it specifically protect from compressive forces?

Answer 5

Composed of collagen fibres and fibroblasts. Protects fasiculi.

Question 6

Surrounding the fascicles and bundling them with the nerve, perineurium protects from what type of force? (see slide 11) It does this because it’s composed mainly of ___?

Answer 6

Stretch.

Composed mainly of collagen fibres and connective tissue (in tight junctions helping maintain fluid pressure).

Question 7

___ surrounds individual nerve fibres and is composed of loose connective tissue.

Answer 7

Endoneurium.

Question 8

With DM2, sensation can be loss due to vascular disease. What supplies blood to nerves (fibroblasts, Schwann cells)?

Answer 8

Arterioles.

Question 9

What is neuropraxia, and how long do its effects last? Are they permanent?

Answer 9

Localized nerve conduction block due to mild compression; temporary resulting in no local damage. Recovery in days to weeks.

Eg. Your leg falls asleep (temp ischemia).

Question 10

With this stretch injury, Wallerian degeneration usually occurs. What is the extent of the damage?

Answer 10

Axonotmesis. Axon breaks before myelin sheath (more extensive).

Question 11

In severe cut or crush injuries, ___ happens. How fast can a PN regenerate?

Answer 11

Neurotmesis. 1 inch per month with the hope of reaching the right afferent.

Question 12

What are the 3 types of compression injuries?

Answer 12

Acute, intermittent (occupational, carpal tunnel), and chronic (longstanding intermittent or constant compression).

Question 13

Name the symptoms of acute / short-term or intermittent PN compression.

Answer 13

• Neuropraxia
• Reduced NCV over compressed segment
• Paresthesia, esp. at night
• Sensory involved before motor
• Pain and temp spared
• Symptoms develop rapidly
• Symptoms short-lived / reversible

Question 14

Name the symptoms of chronic PN compression.

Answer 14

• May develop into axonotmesis
• NCV further reduced or abolished
• Motor denervation
• Pain, allodynia, hyperesthesia
• Symptoms and deficits progressive

Question 15

What are some other causes of neuropathy?

Answer 15

Disease (DM, Guillian Barre), Metabolic (thyroid, DM), Toxins (heavy metals), Genetics (Charot Marie Tooth).

Question 16

Hours after a nerve injury, the PN segment distally begins getting cleaned up and neurotubles and neurofilaments are disarrayed. How many hours does it take before no action potentials can be sent along the nerve (due to swelling)

Answer 16

48-96 hours.

Question 17

What is responsible for phagocytosis?

Answer 17

Mast cells, Schwann cells help, too (36-48 hours).

Question 18

True of false: the endoneurial sheath is not phagocytized.

Answer 18

True. It remains behind as long as it has sufficient blood flow. Can help guide regrowth (with Schwann cells).

Question 19

What is chromatolysis?

Answer 19

The breakdown of Nissl substance 6 hours after nerve injury in the proximal segment. Apoptosis can also occur.

Question 20

Axons require ___ to guide nerve regrowth.

Answer 20

Endoneurial tubes.

Question 21

With denervation of muscle, within 2 months, ___% atrophy. When re-innervated, are all fibres covered?

Answer 21

70% cross sectional area. No, only some. 1 to 1.5 years.

Question 22

Sensory receptors are loyal and wait up to a year for re-innervation. What is it dependent upon?

Answer 22

Axon growth reaching the endoneurial tube / sheath.

Question 23

Regeneration results in?

Answer 23

• More axons due to collaterals
• Smaller diameter initially
• Thinner myelin initially but eventually recovers
• More myelin segments
• Slower conduction velocity

Question 24

Name 3 diseases affecting myelin.

Answer 24

Postinfectious polyneuritis (Guillian Barre), chronic inflammatory demyelinating polyneuropathy (CIDP), multiple sclerosis.

Question 25

With post infectious polyneuritis, young adults are mainly affected and 90% fully recover. What are some symptoms of the disease?

Answer 25

Autoimmune. Fighting of infection turns on myelin. - Ascending weakness (severe) hours to days - Areflexia (loss of DTRs) - Elevated CSF protein - Possible cranial nerve and respiratory involvement - May have mild sensory loss; disproportional motor loss - Inflammatory segmental demyelination Plasmapharesis removes all antibodies.

Question 26

CIDP (autoimmune mediated inflammation) may appear initially as Guillian Barre, affects both sensory and motor and may lead to disability over the long term. What are some treatment options?

Answer 26

- Steroids (short term) - Plasmapheresis - IV IGg People don't always return to previous state of function.

Question 27

What is multiple sclerosis and what are some symptoms?

Answer 27

Neurological deficits in multiple areas of CNS due to damaged myelinated axons. - 4 different types - More common in women (2x more frequent) Symptoms - Sensory (dysesthesia, paresthesia, anesthesia) - Motor (decreased control and spasticity) - Visual - Optic Neuritis - Bladder dysfunction - Brainstem signs - Cerebellar signs - Dementia