Muscle and Neuromuscular Junction Flashcards Preview

Neurology > Muscle and Neuromuscular Junction > Flashcards

Flashcards in Muscle and Neuromuscular Junction Deck (73):
1

what are three characteristics of lower motor neurone disorders?

weak
low tone
fasiculations

2

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

ventral horn of spinal cord

3

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

very fine projections that run along muscle cell

4

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

motor end plate

5

how many motor neurones can one muscle cell respond to?

one

6

how many muscle cells may a single motor neurone control?

many

7

what is the presynaptic process of NMJ?

action potential moves along nerve

voltage gated calcium channels open allowing influx of calcium

vesicles of acetyl choline released into synaptic cleft

8

what is the post synaptic process of NMJ?

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

9

what is the role of acetylcholinesterase?

breaks down acetyl choline into acetate and choline

10

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

sequestered into presynaptic vesicles

11

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

curare (d tubocurarine)

12

what is the fatal consequence of curare?

no muscle contraction so no respiration

13

in what circumstances is curare toxic?

when given IV / IM (1-15 mins)

14

how does novichok work?

inhibits cholinesterase

15

what is clostridium botulinum?

organism present in soil

food and wounds can become infected

IVDU - black tar heroin

16

how does botulinum toxin work?

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

rapid onset weakness without sensory loss

17

what is lambert eaton myasthenic syndrome (LEMS)?

antibodies to presynaptic calcium channels leads to less vesicle release

18

what cancer is strongly associated to LEMS?

small cell carcinoma

19

how is LEMS treated?

3-4 diaminopyridine

20

what is myasthenia gravis?

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

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

21

what is the pathophysiology of MG?

reduced number of ACh receptors and flattening of endplate folds

even with normal ACh the transmission becomes inefficient

22

when do symptoms of MG begin?

when ACh receptors are reduced to 30% of normal

23

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

80-90%

24

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

trigger inflammatory cascades that damage the folds of postsynaptic membrane

25

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

hyperplasia or thymoma

26

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

females in 3rd decade
males in 6th or 7th decade

27

what is the clinical feature of MG?

weakness fluctuating - worse through day

28

what is most common presentation of MG?

extraocular weakness
facial weakness
bulbar weakness

29

limb weakness is typically proximal or distal?

proximal

30

what is the acute treatment of MG?

acetylcholinesterase inhibitor - pyridostigmine

IV immunoglobulin

thymectomy

31

what is long term treatment of MG?

immunomodulating

steroids

steroid sparing agents - azathioprine / mycophenolate

32

what is the emergency treatment of MG?

plasma exchange or immunoglobulin

33

what is biggest drug to avoid in MG?

gentamicin

34

what is mortality of MG?

3-4%

35

what is most common cause of death in MG?

respiratory failure and aspiration pneumonia

36

what is the smallest contractile unit of skeletal muscle?

muscle fibre

37

what is characteristics of muscle fibre?

long, cylindrical structure containing nucleii, mitochondria and sacromeres

38

what surrounds each muscle fibre?

thin layer endomysium

39

20-80 muscle fibres are grouped to form what?

what encapsulates these groups?

fascicle encapsulated by perimysium

40

what surrounds skeletal muscle as a whole?

epimysium

41

what is type I muscle fibre also known as?

slow oxidative

42

what is characteristics of type I muscle fibres?

dense capillary network
myoglobin
resist fatigue

43

what is type IIa muscle fibres also known as?

fast oxidative

44

what is characteristic of type IIa muscle fibres?

aerobic metabolism

45

what is type IIb muscle fibres also known as?

fast glycolytic

46

what is characteristic of type IIb muscle fibres?

easily fatigued

47

what is fasciculations?

visible, fast, fine, spontaneous twitch

48

can fasciculations occur in healthy muscle?

yes - precipitated by stress, caffeine and fatigue

49

in which abnormal muscle can fasciculations occur?

denervated muscle which become hyperexcitable

50

fasciculations are usually a sign of disease where?

motor neurone, not muscle

51

what is myotonia?

failure of muscle relaxation after use

52

what channel is involved in myotonia?

chloride channel

53

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

myalgia
muscle weakness
wasting
hyporeflexia

54

what are examples of immune mediated muscle disease?

dermatomyositis
polymyositis

55

what are examples of inherited muscle disease?

muscular dystrophies
dystrophinopathies
limb girdle muscular dystrophies
myotonic dystrophy

56

what are examples of congenital muscle disease?

congenital myasthenic syndromes
congenital myopathies

57

what is the clinical feature of polymyositis?

symmetrical, progressive proximal weakness developing over weeks to months

58

how is polymyositis treated?

responds to steroids

59

what is the clinical feature of dermatomyositis?

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

60

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

malignancy

61

what is clinical sign of degenerative muscle disease?

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

62

what is the most common muscular dystrophy?

myotonic dystrophy

63

what pattern of inheritance is myotonic dystrophy?

autosomal dominant

64

what is symptoms of myotonic dystrophy?

myotonia
weakness
cataracts
ptosis
frontal balding
cardiac defects

65

what type of disorder is myotonic dystrophy?

trinucleotide repeat disorder with anticipation

66

what are other 2 common muscular dystrophies?

duchenne and becker

67

what are infective causes of muscle disease?

viral - coxsacchie
trypanosomiasis
cistercercosis - undercooked pork
borrelia

68

what are toxic causes of muscle disease?

drugs
venoms

69

what causes rhabdomyolysis?

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

70

what is the triad of clinical features of rhabdomyolysis?

myalgia
muscle weakness
myoglobinuria

71

what are 2 complications of rhabdomyolysis?

acute renal failure
disseminated intravascular coagulation

72

what are the 5 grades of MRC muscle power?

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

what is rhabdomylosis?

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