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Neurology > Muscle and Neuromuscular Junction > Flashcards

Muscle and Neuromuscular Junction Flashcards

1
Q

what are three characteristics of lower motor neurone disorders?

A

weak
low tone
fasiculations

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2
Q

where do the cell bodies of motor neurones which innervate skeletal muscle arise?

A

ventral horn of spinal cord

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3
Q

what does the terminal portion of motor neurones give rise to?

A

very fine projections that run along muscle cell

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4
Q

what name is given to the synapses formed between motor neurones and muscle?

A

motor end plate

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5
Q

how many motor neurones can one muscle cell respond to?

A

one

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6
Q

how many muscle cells may a single motor neurone control?

A

many

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7
Q

what is the presynaptic process of NMJ?

A

action potential moves along nerve

voltage gated calcium channels open allowing influx of calcium

vesicles of acetyl choline released into synaptic cleft

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8
Q

what is the post synaptic process of NMJ?

A

acetyl choline diffuses across synaptic cleft

the acetyl choline receptor opens and renders membrane permeable to Na / K ions

the depolarisation starts an action potential at motor end plate

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9
Q

what is the role of acetylcholinesterase?

A

breaks down acetyl choline into acetate and choline

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10
Q

what happens to choline after it being formed from breakdown of acetylcholine?

A

sequestered into presynaptic vesicles

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11
Q

what is name given to substance which occupies same position on ACh receptor but does not open ion channel?

A

curare (d tubocurarine)

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12
Q

what is the fatal consequence of curare?

A

no muscle contraction so no respiration

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13
Q

in what circumstances is curare toxic?

A

when given IV / IM (1-15 mins)

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14
Q

how does novichok work?

A

inhibits cholinesterase

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15
Q

what is clostridium botulinum?

A

organism present in soil

food and wounds can become infected

IVDU - black tar heroin

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16
Q

how does botulinum toxin work?

A

cleaves presynaptic proteins involved in vesicle formation and blocks vesicle docking with presynaptic membrane

rapid onset weakness without sensory loss

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17
Q

what is lambert eaton myasthenic syndrome (LEMS)?

A

antibodies to presynaptic calcium channels leads to less vesicle release

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18
Q

what cancer is strongly associated to LEMS?

A

small cell carcinoma

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19
Q

how is LEMS treated?

A

3-4 diaminopyridine

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20
Q

what is myasthenia gravis?

A

autoimmune disorder where antibodies produced to acetyl choline receptors (AChR)

this causes reduced number of functioning receptors which leads to muscle weakness and fatiguability

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21
Q

what is the pathophysiology of MG?

A

reduced number of ACh receptors and flattening of endplate folds

even with normal ACh the transmission becomes inefficient

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22
Q

when do symptoms of MG begin?

A

when ACh receptors are reduced to 30% of normal

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23
Q

in what percentage of patients with MG are ACh antibodies found?

A

80-90%

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24
Q

as well as blocking binding of ACh, what else to the antibodies do in MG?

A

trigger inflammatory cascades that damage the folds of postsynaptic membrane

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25
Q

as thymus plays a role in MG, 75% patients also have what other conditions?

A

hyperplasia or thymoma

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26
Q

MG may occur at any age but what are the two peaks of incidence?

A

females in 3rd decade

males in 6th or 7th decade

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27
Q

what is the clinical feature of MG?

A

weakness fluctuating - worse through day

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28
Q

what is most common presentation of MG?

A

extraocular weakness
facial weakness
bulbar weakness

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29
Q

limb weakness is typically proximal or distal?

A

proximal

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30
Q

what is the acute treatment of MG?

A

acetylcholinesterase inhibitor - pyridostigmine

IV immunoglobulin

thymectomy

31
Q

what is long term treatment of MG?

A

immunomodulating

steroids

steroid sparing agents - azathioprine / mycophenolate

32
Q

what is the emergency treatment of MG?

A

plasma exchange or immunoglobulin

33
Q

what is biggest drug to avoid in MG?

A

gentamicin

34
Q

what is mortality of MG?

35
Q

what is most common cause of death in MG?

A

respiratory failure and aspiration pneumonia

36
Q

what is the smallest contractile unit of skeletal muscle?

A

muscle fibre

37
Q

what is characteristics of muscle fibre?

A

long, cylindrical structure containing nucleii, mitochondria and sacromeres

38
Q

what surrounds each muscle fibre?

A

thin layer endomysium

39
Q

20-80 muscle fibres are grouped to form what?

what encapsulates these groups?

A

fascicle encapsulated by perimysium

40
Q

what surrounds skeletal muscle as a whole?

41
Q

what is type I muscle fibre also known as?

A

slow oxidative

42
Q

what is characteristics of type I muscle fibres?

A

dense capillary network
myoglobin
resist fatigue

43
Q

what is type IIa muscle fibres also known as?

A

fast oxidative

44
Q

what is characteristic of type IIa muscle fibres?

A

aerobic metabolism

45
Q

what is type IIb muscle fibres also known as?

A

fast glycolytic

46
Q

what is characteristic of type IIb muscle fibres?

A

easily fatigued

47
Q

what is fasciculations?

A

visible, fast, fine, spontaneous twitch

48
Q

can fasciculations occur in healthy muscle?

A

yes - precipitated by stress, caffeine and fatigue

49
Q

in which abnormal muscle can fasciculations occur?

A

denervated muscle which become hyperexcitable

50
Q

fasciculations are usually a sign of disease where?

A

motor neurone, not muscle

51
Q

what is myotonia?

A

failure of muscle relaxation after use

52
Q

what channel is involved in myotonia?

A

chloride channel

53
Q

what are the 4 main signs / symptoms of muscle disease?

A

myalgia
muscle weakness
wasting
hyporeflexia

54
Q

what are examples of immune mediated muscle disease?

A

dermatomyositis

polymyositis

55
Q

what are examples of inherited muscle disease?

A

muscular dystrophies
dystrophinopathies
limb girdle muscular dystrophies
myotonic dystrophy

56
Q

what are examples of congenital muscle disease?

A

congenital myasthenic syndromes

congenital myopathies

57
Q

what is the clinical feature of polymyositis?

A

symmetrical, progressive proximal weakness developing over weeks to months

58
Q

how is polymyositis treated?

A

responds to steroids

59
Q

what is the clinical feature of dermatomyositis?

A

similar to polymyositis but also has skin lesions - heliotrope rash on face

60
Q

up to 50% of patients with dermatomyositis have underlying what?

A

malignancy

61
Q

what is clinical sign of degenerative muscle disease?

A

typically slowly progressive weakness in 6th decade with characteristic thumb sparing

62
Q

what is the most common muscular dystrophy?

A

myotonic dystrophy

63
Q

what pattern of inheritance is myotonic dystrophy?

A

autosomal dominant

64
Q

what is symptoms of myotonic dystrophy?

A 
myotonia 
weakness
cataracts 
ptosis 
frontal balding 
cardiac defects
65
Q

what type of disorder is myotonic dystrophy?

A

trinucleotide repeat disorder with anticipation

66
Q

what are other 2 common muscular dystrophies?

A

duchenne and becker

67
Q

what are infective causes of muscle disease?

A

viral - coxsacchie
trypanosomiasis
cistercercosis - undercooked pork
borrelia

68
Q

what are toxic causes of muscle disease?

A

drugs

venoms

69
Q

what causes rhabdomyolysis?

A

many things eg crush injuries, toxins, post convulsions and extreme exercise

70
Q

what is the triad of clinical features of rhabdomyolysis?

A

myalgia
muscle weakness
myoglobinuria

71
Q

what are 2 complications of rhabdomyolysis?

A

acute renal failure

disseminated intravascular coagulation

72
Q

what are the 5 grades of MRC muscle power?

A

0 = no movement

1 = flicker of movement when attempting to contract muscle

2 = some movement if gravity removed but none against gravity

3 = movement against gravity but not against resistance

4 = movement against resistance but not full strength

5 = normal strength

73
Q

what is rhabdomylosis?

A

damage to skeletal muscle causes leakage of large quantities of toxic intracellular contents into plasma

Neurology (32 decks)

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