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Neurology > Muscle and Neuromuscular Junction Dysfunction > Flashcards

Muscle and Neuromuscular Junction Dysfunction Flashcards

1
Q

What are the symptoms of lower motor neuron disorders?

A

Weakness, low tone, fasciculations

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2
Q

What innervates skeletal muscle fibres?

A

Motor neurons = these have their cell bodies arise in the ventral horn of the spinal cord

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3
Q

What does the terminal portion of the motor neurons give rise to?

A

Very fine projections that run along the muscle cell

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4
Q

What are motor end plates?

A

Synapses formed between motor neurons and muscle

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5
Q

What is special about motor units?

A

A single motor neuron may control many muscle cells but each muscle cell only responds one motor neuron

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6
Q

What initiates muscle contraction?

A

AP moves along nerve = voltage gated Ca2+ channels open allowing calcium influx which releases vesicles of ACh into the synaptic cleft

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7
Q

What happens when ACh diffuses across the synaptic cleft?

A

Receptors open and render the membrane permeable to Na+/K+ = depolarisation starts an AP at the motor end plate

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8
Q

What is curare?

A

Plant extract = occupies same position on ACH receptor but doesn’t open ion channel, stops muscle contraction so respiration ceases

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9
Q

What are some presynaptic disorders?

A

Botulism and Lambert-Eaton myasthenic syndrome

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10
Q

What causes botulism?

A

Clostridium botulinium = present in soil, wounds and food can become infected, common in IV drug users (black tar heroin)

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11
Q

What occurs in botulism?

A

Cleaves presynaptic proteins involved in vesicle formation and blocks vesicle docking with the presynaptic membrane

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12
Q

What is the presentation of botulism?

A

Rapid onset weakness without sensory loss

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13
Q

What are some features of Lambert-Eaton myasthenic syndrome?

A

Antibodies to presynaptic Ca2_ channels leads to less vesicle release = strong association with small cell carcinoma, treated with 3-4 diaminopyridine

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14
Q

What is myasthenia gravis?

A

Postsynaptic disorder = most common NMJ disorder, auto-immune with antibodies to ACh receptors

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15
Q

What causes symptoms in myasthenia gravis?

A

Reduced number of functioning receptors leads to muscle weakness and fatiguability = symptoms occur when receptors reduced to 30% of normal

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16
Q

What effect do ACh antibodies have in myasthenia gravis?

A

Found inn 80-90% = block binding of ACh, also trigger inflammatory cascade that damage the folds of postsynaptic membrane (causes flattening)

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17
Q

How relevant is the thymus in myasthenia gravis?

A

Seems to play a role = 75% have hyperplasia or thymoma

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18
Q

What is the epidemiology of myasthenia gravis?

A

Peaks in females in 30s and males age 60-70

More common in women

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19
Q

What are the features of myasthenia gravis?

A

Weakness typically fluctuating = worse throughout day
Limb weakness is usually proximal
Most common presentation is extra-ocular, facial and bulbar weakness

20
Q

What is the acute treatment of myasthenia gravis?

A

Acetylcholinesterase inhibitor = pyridostigmine
IV immunoglobulin
Thymectomy = even in absence of thymus abnormality

21
Q

What is the general treatment of myasthenia gravis?

A

Immunomodulating, steroids, azathioprine or mycophenolate

22
Q

What drug should be avoided in myasthenia gravis?

A

Gentamicin

23
Q

What tends to cause death in myasthenia gravis?

A

Respiratory failure and aspiration pneumonia

24
Q

What are some features of skeletal muscle?

A

Highly organised = each muscle fibre surrounded by thin layer endomysium, 20-80 grouped together to form fascicle encapsulated by perimysium

25
Q

What is the smallest contractile unit of skeletal muscle?

A

The muscle fibre = long and cylindrical, contains nuclei, mitochondria and sarcomeres

26
Q

What are some features of smooth muscle?

A

Cell not striated and gap junctions between cells
Single central nucleus and no sarcomeres
Actin to myosin ratio is 10:1
Significant connective tissue around them

27
Q

What are the types of smooth muscle fibre?

A

Type I = slow oxidative, dense capillary network, myoglobin, resist fatigue
Type IIa = fast oxidative, aerobic metabolism
Type IIb = fast glycolytic, easily fatigued

28
Q

What are fasciculations?

A

Visible, fast, fine, spontaneous twitches = occurs in denervated muscle which becomes hyperexcitable

29
Q

What do fasciculations mean?

A

Can occur in healthy muscle = stress, caffeine, fatigue

Usually a sign of motor neuron (not muscle) disease

30
Q

What are the symptoms of muscle disease?

A

Myalgia, wasting, hyporeflexia, muscle weakness

31
Q

What are some examples of immune mediated muscle disease?

A

Polymyositis and dermatomyositis

32
Q

What are some features of polymyositis?

A

Symmetrical progressive proximal weakness = develops over weeks, raised CK, responds to steroids

33
Q

What are some features of dermatomyositis?

A

Associated with skin lesions = heliotrope rash of face

Up to 50% have underlying malignancy

34
Q

What are some examples of congenital muscle diseases?

A

Congenital myasthenic syndromes

Congenital myopathies

35
Q

What are some examples of inherited muscle diseases?

A

Muscular dystrophies, dystrophinopathies, limb girdle muscular dystrophies, myotonic dystrophies

36
Q

What are some features of degenerative muscle diseases?

A

Inclusion body myositis = thought to be inflammatory but little response to steroids, slowly progressive weakness, begins in 60s, thumbs are spared

37
Q

What is the most common muscular dystrophy?

A

Myotonic dystrophy = autosomal dominant, trinucleotide repeat disorder with anticipation

38
Q

What are the features of muscular dystrophy?

A

Multisystem involvement = myotonia, weakness, cataracts, ptosis, frontal balding, cardiac defects

39
Q

What are some features of inherited muscular dystrophies?

A

Non-inflammatory and progressive = non central or peripheral nerve abnormality, Duchenne and Becker dystrophies are most common

40
Q

What occurs in rhabdomyolysis?

A

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

41
Q

What are some causes of rhabdomyolysis?

A

Crush injuries, toxins, post convulsion, extreme exercise

42
Q

What are some features of rhabdomyolysis?

A

Triad of myalgia, muscle weakness and myoglobinuria

May lead to acute renal failure or DIC

43
Q

What is done when examining muscle?

A

Inspection and palpation, strength testing, neck and core strength assessment, fatiguability

44
Q

What are grades 0-2 of the MRC muscle power grading?

A 
0 = no movement at all
1 = flicker of movement when trying to contract muscle
2 = some movement if gravity removed but none against gravity
45
Q

What are grades 3-5 of the MRC muscle power grading?

A 
3 = movement against gravity but not resistance
4 = movement against resistance but not full strength
5 = Normal strength

Neurology (48 decks)

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