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Patho 2 > Chap 27- Peripheral nerves and skeletal muscles > Flashcards

Chap 27- Peripheral nerves and skeletal muscles Flashcards

1
Q

structure of skeletal muscles

A

bundle of muscle fibers -> muscle fiber -> myofibril -> actin and myosin

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2
Q

fascia

A
  • CT covering entire muscle

- located over layer of epimysium

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3
Q

epimysium

A
  • CT that wraps around whole muscle

- continuation of tendon

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4
Q

perimysium

A
  • covers each bundle of muscle fibers
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5
Q

endomysium

A
  • CT that wraps each individual muscle fiber
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6
Q

sarcolemma

A
  • cell membrane of muscle fibers
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7
Q

excitation contraction coupling

A
  • electrical impulse triggers release of Ca from SR
  • ACh is released at NMJ
  • muscle contraction occurs
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8
Q

common characteristics of NMJ diseases

A
  • painless

- weakness

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9
Q

myasthenia gravis

A
  • autoantibodies against ACh receptors causes aggregation and degradation of receptors
  • bimodal age distribution young females or older males
  • leads to reduced muscle contractions
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10
Q

myasthenia gravis clinical features

A
  • progressive generalized weakness exacerbated by exertion
  • weakness starts at eyes
  • can have focal muscle weakness if anitbodies against different parts
  • highly linked to thymic disorders
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11
Q

lambert-eaton myasthenic syndrome

A
  • antibodies against presynaptic Ca channel
  • causes repetitive stimulation of muscles
  • weakness in lower extremities then moves up
  • usually have underlying malignancies
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12
Q

why is LEM associated with cancer?

A
  • antibodies are formed against cancer cells

- antibodies are similar to Ca channels

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13
Q

neurogenic disease atrophy

A
  • clusters or groups of fibers are atrophied
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14
Q

perifascicular atrophy

A
  • atrophy on periphery of muscle bundle

- seen in dermatomyositis

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15
Q

type II fiber atrophy

A
  • seen in prolonged corticosteroid use
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16
Q

dermatomyositis

A
  • autoimmune disease
  • proximal muscle weakness and skin changes
  • can also affect joints, esophagus, lungs
  • happens in children and older adults
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17
Q

clinical features of dermatomyositis

A
  • proximal muscle weakness
  • myalgia
  • elevated CK
  • heliotrope rash
  • gottron papules
  • dysphagia
  • lung disease
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18
Q

what are gottron papules?

A
  • scaling eruptions on knuckles, elbows and knees

- characteristic of dermatomyositis

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19
Q

pathogenesis of dermatomyositis

A
  • autoimmune attack against endothelium of capillaries
  • activates complement system -> MAC formation
  • endothelial necrosis -> cytokine recruitment
  • adhesion molecules expressed
  • CD4 cells and macrophages bind to adhesion molecules
  • ischemia
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20
Q

polymyositis

A
  • dx of exclusion
  • lacks distinctive cutaneous features
  • adult onset
  • proximal muscle weakness and myalgia
  • can involve other systems
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21
Q

what are the main inflammatory . mediators of polymyositis?

A

CD8+

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22
Q

inclusion body myositis

A
  • disease of late adulthood
  • slowly progressing muscle weakness of distal muscles
  • no autoantibodies
  • debate on if it is primary or secondary disease
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23
Q

what are inclusion bodies?

A

abnormal protein aggregates inside muscle cells

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24
Q

chloroquine toxic myopathy

A
  • drug induced lysosomal storage myopathy
  • inhibits autophagy
  • presents with slowly progressive muscle weakness
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25
Q

ICU myopathy

A
  • degredation of sarcomeric myosin thick filaments
  • produces profound weakness
  • commonly occurs due to corticosteroid use
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26
Q

thyrotoxic myopathy

A
  • acute or chronic proximal muscle weakness
  • excess thyroid hormone inhibits AChI
  • causes muscle fatigue due to too much activity
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27
Q

hypothyroidism myopathy

A
  • cramping or aching muscles
  • decreased movement
  • slowed reflexes
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28
Q

alcohol myopathy

A
  • binge drinking can cause rhabdo, myoglobinuria, renal failure
  • causes direct muscle fiber lysis
29
Q

congenital myopathy

A
  • defect in excitation- contraction coupling unit
  • seen at birth
  • mostly nonprogressive
  • normal CK levels
30
Q

muscular dystrophy

A
  • sx present typically later in life
  • membrane damage causes necrosis
  • progressive weakness
  • elevated CK levels
31
Q

muscular dystrophies with defects in extracellular matrix

A
  • ullrich congenital MD

- merosin deficiency

32
Q

duchene MD

A
  • mutation in dystrophin
  • x-linked
  • severe progressive phenotype
  • no inflammation except myophagocytosis
33
Q

what does dystrophin typically do?

A
  • mechanical stability to myofiber and cell membrane during contraction
  • defects causes influx of Ca
34
Q

clinical features of DMD

A
  • normal at birth
  • pseudohypertrophy
  • weakness begins in pelvic girdle then extends to shoulders
  • joint contractures, scoliosis, worsening respiratory reserve, sleep hypoventilation
  • heart and brain problems
35
Q

limb girdle muscular dystrophy

A
  • muscle weakness that preferentially involves proximal muscle groups
  • age and severity highly variable
36
Q

myotonic dystrophy

A
  • autosomal dominant
  • myotonia
  • muscle weakness, cataracts, endocrinopathy, cardiomyopathy
37
Q

pathogenesis of myotonic dystrophy

A
  • expansion of CTG triplet repeats in DMPK gene
  • DMPK is important in RNA splicing leading to defective chloride channels
  • muscle cannot easily relax
38
Q

spinal muscular atrophy

A
  • loss of motor neurons
  • causes weakness and atrophy of voluntary muscles
  • autosomal recessive
  • affects muscles closest to center of the body
39
Q

what causes spinal muscular atrophy?

A
  • loss of function mutation in SMN1 gene
40
Q

what is the hallmark of spinal muscular atrophy

A
  • generalized hypotonia -> floppy infant
41
Q

classifications of diseases of lipid/glycogen metabolism

A
  • exercise or fasting -> muscle cramping/pain and rhabdo

- slowly progressive muscle damage

42
Q

carnitine palmitoyltransferase II deficiency

A
  • most common disorder or lipid metabolism
  • causes episodic muscle damage when exercising or fasting
  • impairs transport of FFA into mitochondria
43
Q

myophosphorylase deficiency

A
  • aka McArdle disease
  • common glycogen storage diseases affecting skeletal muscle
  • causes episodic muscle damage with exercise
44
Q

Acid maltase deficiency

A
  • impaired lysosomal conversion of glycogen to glucose
  • causes glycogen to accumulate in lysosomes
  • tx with enzyme replacement therapy
45
Q

types of acid maltase deficiency

A
  • severe= Pompe disease

- mild = adult onset myopathy

46
Q

mitochondrial myopathies manifestations

A
  • weakness
  • elevated serum creatine kinase levels
  • rhabdo
  • chronic progressive external opthalmoplegia common- clue for dx
  • maternally inherited
47
Q

pathologic change seen in mitochondrial myopathies

A
  • abnormal aggregates of mitochondria
  • found in subsarcolemmal area of affected myofibers
  • looks like ragged red fibers
48
Q

ion channel myopathies

A
  • affects fn of ion channel proteins

- manifestation depends on channel affected`

49
Q

broad classifications of ion channel myopathies

A
  • increase excitability -> hypertonia

- decreased excitability -> hypotonia -> hyperk/hypok/ normok -> periodic paralysis

50
Q

KCNJ2

A
  • potassium channel mutation -> hypokalemia
  • causes andersen-twail syndrome
  • period paralysis
  • heart arryhthmias
  • skeletal abnormalities
51
Q

SCN4A

A
  • Na channel mutation

- presents as many differet disorders i.e. myotonia or hyperk periodic paralysis

52
Q

CACNA1S

A
  • Ca channel mutation

- most common cause of hypokalemic paralysis

53
Q

CLC1

A
  • Cl channel mutation

- causes myotonia congenita

54
Q

RYR1

A
  • mutation affecting Ca sensitive Ca channels
  • RYR causes release of Ca into cytoplasm from SR
  • causes malignant hyperthermia
55
Q

Axons

A

projection that transmits impulses away from cell body

56
Q

dendrites

A

projection that transmits impulses toward cell body

57
Q

terminal boutons

A

bulges at end of axon that communicate with neurons, muscle fibers, or glands

58
Q

myelin sheath

A

surrounds axons and increases rate of impulse transmission

59
Q

schwann cells

A

produce myelin sheath

60
Q

nodes of ranvier

A

separate schwann cells

61
Q

synapes

A
  • gap between neurons

- made up of presynaptic terminal, synaptic cleft, and postsynaptic cell membrane

62
Q

some causes of peripheral nerve damage

A
  • inflammatory diseases
  • infections
  • metabolic changes
  • toxic injury
  • trauma
  • paraneoplastic disease
  • inherited gene defects
63
Q

Guillain- Barre Syndrome (GBS)

A
  • demyelinating peripheral neuropathy
  • ascending paralysis
  • can affect respiratory muscles
64
Q

GBS pathogenesis

A
  • associated with certain infections or prior vaccination
  • T cell mediated immune response causes segmental demyelination that is induced by macrophages
  • circulating Ig react with peripheral nerves
65
Q

GBS clinical features

A
  • ascending paralysis
  • areflexia
  • sensory involvement- loss of pain sensation
  • slowed nerve conduction
  • elevated CSF due to increased permeability of microcirculation
66
Q

what is the most common cause of peripheral neuropathies?

A

diabetes

67
Q

pathogenesis of diabetic neuropathy

A
  • hyperglycemia -> glycosyation -> decreased protein fn and activated inflammatory signaling
  • excess glucose -> conv to sorbitol -> increased ROS -> nerve damage
68
Q

clinical features of diabetic polyneuropathy

A
  • numbness, loss of pain sensation, paresthesia, dysestheisa
  • difficulty with balance
  • ANS dysfunction
  • postural hypotension
  • sexual dysfunction
  • incomplete bladder emptying

Patho 2 (15 decks)

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