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NEUROLOGY > Muscles and the Neuromuscular Junction > Flashcards

Muscles and the Neuromuscular Junction Flashcards

1
Q

What symptoms and signs are usually present in a lower motor neuron disorder?

A

Weakness
low muscle tone
fasiculations

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2
Q

What symptoms and signs usually present in an upper motor neuron disorder?

A

Stiffness
Spasticity
Increased tone

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3
Q

Neuromuscular junctions (NMJ) join which two parts of the peripheral nervous system?

A

Motor neuron + muscle

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4
Q

What name other than NMJ is given to the synapses formed between motor neurons and muscle?

A

motor end plate

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5
Q

Describe how Acetylcholine is released into the NMJ?

A 
AP at presynaptic membrane
Ca2+ influx
Vesicles of ACh released
This diffuses across synaptic cleft
Picked up by ACh receptors
Opens Na/K channels to depolarise post-synaptic membrane
AP generated
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6
Q

What toxin is known to cause complete failure of muscular contraction and what are the consequences of this?

A

Curare

- causes respiratory failure

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7
Q

Give examples of pre-synaptic causes of NMJ dysfunction

A
  • abnormality of Ca2+, Mg2+ or Na+ channels
  • Clinical botulism
  • lambert-eaton syndrome
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8
Q

How does botox affect the pre-synaptic terminal involved in muscle contraction?

A
  • block vesicle docking in presynaptic membrane

=> Rapid onset weakness without sensory loss.

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9
Q

How does Lambert-Eaton syndrome affect the NMJ, and what could be an underlying cause for this?

A
  • antibodies to pre-synaptic Ca2+ channels
    => less vesicle release

Strong association with small cell carcinoma

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10
Q

Is Myasthenia Gravis a pre-synaptic or post-synaptic disorder of the NMJ?

A

Post-synaptic

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11
Q

Explain the pathophysiology of Myasthenia Gravis

A

Autoimmune - antibodies to acetylcholine receptors

=> Reduced number of functioning receptors
=> muscle weakness and fatiguability

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12
Q

What percentage of receptors remain to be working when symptoms start in myasthenia gravis?

A

symptoms start when ACh receptors reduced to 30% of normal

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13
Q

Why do patients with myasthenia gravis often have a “Square smile”?

A

They have bilateral facial weakness

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14
Q

Why may patients with myasthenia gravis appear to have excessive wrinkles on their forehead?

A

They have ptosis of the eyelids

=> are holding their eyebrows up high to keep eyes open

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15
Q

What percentage of myasthenia gravis patients are found to have antibodies against ACh?

A

80-90%

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16
Q

What other structure in the body can contribute to myasthenia gravis?

A

Thymus => 75% patients have hyperplasia or thymoma

  • removing thyroid can often reverse disease in these cases
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17
Q

What is the female:male ratio of patients with myasthenia gravis and at what age does incidence of the disease in each gender peak?

A

female:male ratio - 3:2

females in 30s
males in 60s-70s

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18
Q

What symptoms do patients with myasthenia gravis usually notice?

A
  • Weakness - gets worse through the day
    => give up chewing food, keeping eyes open
  • extraocular, facial and bulbar weakness
  • Limb weakness typically proximal
19
Q

How is myasthenia gravis treated acutely?

A

ACh inhibitor - Pyridostigmine
IV immunoglobulin to mop up Antibodies
Thymectomy

20
Q

What long-term treatment is available for myasthenia gravis?

A
  • immunomodulating
  • steroids (prednisolone)
  • Steroid sparing agents (these take 12 weeks for peak action to occur) e.g. azathioprine, mycophenelate
  • Emergency treatment = plasma exchange or IV Ig
21
Q

What clinical features of myasthenia gravis are most likely to cause morbidity?

A

respiratory failure and aspiration pneumonia

22
Q

What drug can potentially precipitate myasthenic crisis

A

Gentamicin

23
Q

What is a fasiculation of muscle?

A

Visible, fast, fine , spontaneous twitch

24
Q

When are fasiculations of muscle usually seen?

A

Physiologically => in healthy muscle – precipitated by stress, caffeine, fatigue (after exercise etc)

Occur in denervated muscle which become hyperexcitable

=> more a problem with motor neuron than muscle

25
Q

What is myotonia?

A

Failure of muscle relaxation after use
=> remains contracted for too long

Chloride channels don’t stop electrical excitation quickly enough

26
Q

What symptoms may indicate muscle disease?

A
  • Myalgia (pain)
  • Muscle weakness – often specific patterns eg proximal limbs in Polymyositis
  • Wasting
  • Hyporeflexia
27
Q

What inflammatory causes of muscle disease exist?

A

Polymyositis

  • symmetrical, progressive proximal weakness
  • Raised CK - responds to steroid

Dermatomyositis
- Similar to above but with Heliotrope rash on face

28
Q

Give an example of a degenerative muscle disease

A

Inclusion body myositis

  • slowly progressive weakness
  • 60s
  • Characteristic thumb sparing

Historically thought to be inflammatory but little response to steroids

29
Q

What inheritance pattern do genetic muscular dystrophies follow?

A

Autosomal dominant

30
Q

What are the usual clinical features in myotonic dystrophies?

A
  • Myotonia (prolonged contraction)
  • weakness
  • ptosis
  • cataracts
  • frontal balding
  • cardiac defects
31
Q

What muscular dystrophy is most commonly known?

A

Duchenne Muscular dystrophy

32
Q

What congenital muscle problems can occur?

A

Congenital myasthenic syndromes

Congenital myopathies

33
Q

If a patient has weakness in their neck muscles causing an inability to keep their head up, what 4 pathologies should you consider?

A

Muscle disorder
Myopathy
Myositis
Motor Neurone Disease

34
Q

What infections have the potential to cause a muscle disorder?

A

Coxsackie virus
Trypanosomiasis (uncooked pork)
Borrelia

35
Q

What toxins can potentially cause a muscle disorder?

A

Drugs (e.g. statins)

Venoms (countries other than UK)

36
Q

What muscle disorders can be caused by statins

A

myopathies
myalgia
persistent myositis (autoimmune)

37
Q

What group of drugs are known to cause muscle weakness?

38
Q

What is rhabdomyolysis?

A

damage to skeletal muscle
=> leaks a lot of toxic intracellular contents into plasma
=> kidneys struggle to excrete this

39
Q

What can potentially cause rhabdomyolysis?

A
  • crush injuries
  • toxins
  • post-convulsions
40
Q

What clinical features indicate rhabdomyolysis?

A

myalgia
muscle weakness
myoglobinuria

41
Q

What are the consequences of rhabdomyolysis?

A
  • acute renal failure

- Disseminated intravascular coagulation (DIC) (excessive clotting)

42
Q

How would fatiguability of a muscle be tested?

A
  • Test movement (power normal)
  • Exercise muscle you are wanting to fatigue
  • Test movement again when muscle is tired
43
Q

How is power of a muscle recorded?

A

Scale of 0-5
0 - No movement
1 - Flicker of muscle
2 - Some movement if gravity is REMOVED
3 - Movement against gravity but NOT resistance
4 - Movement against resistance but NOT full strength
5 - Normal strength

NEUROLOGY (29 decks)

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