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Neurology > Muscle and the NMJ > Flashcards

Muscle and the NMJ Flashcards

1
Q

What characterises LMN disorders?

A

Weakness
Low tone
Fasiculations

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2
Q

Where do the cell bodies of motor neurons which innervate skeletal muscle fibres arise from?

A

The ventral horn of the spinal cord

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3
Q

What do the terminal portion of skeletal muscle fibres give rise to?

A

Very fine projection ions that run along the muscle cell

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4
Q

What are the synapses formed between motor neurons and muscle called?

A

The motor end plate

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5
Q

What is the rule regarding motor neurons and muscle cells?

A

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

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6
Q

Describe neurotransmission at the NMJ

A

AP moves along nerve
Voltage-gated Ca+ open allowing Ca+ influx
Vesicles of acetylcholine released into cleft
Acetylcholine diffuses across cleft
Acetylcholine receptor opens and renders the membrane permeable to Na+/K+ ions
Depolarisation starts an AP at the motor end plate

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7
Q

What is the action of acetylcholinesterase?

A

Splits acetylcholine into acetate and choline

Choline is then sequestered into presynaptic vesicles

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8
Q

Describe curare

A

D tubocurarine
Occuies same position on ACh receptor but does not open ion channels
No muscle contraction- so no respiration
Only toxic IV/IM (1-15min)

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9
Q

Where is clostridium botulinum found?

A

Soil
Food and wounds can become infected
IV drug users- black tar heroin

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10
Q

What does botulinum toxin do?

A

Cleaves presynaptic proteins involved in vesicle formation and block vesicle docking with the presynaptic membrane.
Rapid onset weakness without sensory loss.
Some medical and cosmetic uses

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11
Q

What is Lambert Eaton Myasthenic Syndrome?

A

Antibodies to presynaptic calcium channels leads to less vesicle release. Strong association with underlying small cell carcinoma

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12
Q

What are some presynaptic disorders?

A

Botulism

Lambert Eaton Myasthenic Syndrome

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13
Q

What is an example of a post synaptic disorder?

A

Myasthenia Gravis

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14
Q

Describe Myasthenia Gravis

A

Most common NMJ disorder
AI- antibodies to acetyl choline receptors (AChR)
Reduced number of functioning receptors leads to muscle weakness and fatiguability

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15
Q

What is the pathophysiology of Myasthenia Gravis?

A

Reduced number of ACh receptors and flattening of endplate folds
Even with normal amounts of ACh transmission becomes inefficient
Symptoms start when AChR reduced to 30% of normal

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16
Q

What do ACh antibodies do?

A

Block binding of ACh but also trigger inflammatory cascades that damage the fold of the postsynaptic membrane (thymus plays a role, 75% have hyperplasia or thymoma)

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17
Q

When does myasthenia usually present in females and males?

A

Females 3rd decade
Males 6/7th decade
F:M 3:2

18
Q

What are the clinical features of Myasthenia Gravis?

A

Weakness typically fluctuating-worse through day
Extraocular, facial and bulbar weakness
Limb weakness typically proximal

19
Q

What is the treatment for MG?

A 
Acetylcholinesterase inhibitor-pyridostigmine
Thymectomy
Immunomodulating
Steroids/azathioprine
Emergency- plasma exchange or Ig
20
Q

What usually causes morbidity in MG patients?

A

Resp failure

Aspiration pneumonia

21
Q

Describe skeletal muscle

A

Smallest contractile unit is the muscle fibre-long, cylindrical, containing nuclei, mitochondria, sarcomeres
Each surrounded by endomysium
20-80 group to form fascicle encapsulated by perimysium
Large number of these ensheathed in epimysium-forms individual muscle

22
Q

Describe smooth muscle

A 
Non-striated cells
Single central nucleus
Gap junctions between cells
Connective tissue around them
No sarcomeres
Actin:myosin 10:1
23
Q

What are the 3 muscle fibre types?

A

Type I, IIa, IIb

24
Q

Describe Type I muscle fibres

A

Slow oxidative

Dense capillary network, myoglobin, resist fatigue

25
Q

Describe Type IIa muscle fibres

A

Fast oxidative

Aerobic metabolism

26
Q

Describe Type IIb muscle fibres

A

Fast glycolytic

Easily fatigued

27
Q

What are fasciculations?

A

Visible, fast, fine spontaneous twitch

28
Q

When may fasciculations occur?

A

In healthy muscle-precipitated by stress, caffeine, fatigue
In denervated muscle which may become hyperexcitable
Usually a sign of disease in motor neurone, not muscle

29
Q

What is myotonia?

A

Failure of muscle relaxation after use

Due to chloride channel dysfunction

30
Q

What are some symptoms/signs of muscle disease?

A

Myalgia
Muscle weakness- often specific patterns of weakness depending on cause e.g. proximal limbs in polymyositis
Wasting
Hyporeflexia

31
Q

What are some inflammatory muscle diseases?

A

Dermatomyositis

Polymyositis

32
Q

What are some inherited muscle diseases?

A

Muscular dystrophies
Dystrophinopathies
Limb girdle muscular dystrophies
Myotonic dystrophy

33
Q

What are some congenital muscle diseases?

A

Congenital myasthenic syndromes

Congenital myopathies

34
Q

Describe polymyositis

A

Symmetrical, progressive proximal weakness developing over weeks to months
Raised CK- responds to steroid

35
Q

Describe dermatomyositis

A

Clinically similar to polymyositis but assoc with skin lesions
Heliotrope rash on face
Up to 50% have underlying malignancy

36
Q

Describe inclusion body myositis

A

Degenerative
Little response to steroid
Typically slowly progressive weakness in 6th decade of life with characteristic thumb sparing

37
Q

Describe myotonic dystrophy

A

Commonest muscular dystrophy
AD
Multisystem
Trinucleotide repeat disorder with anticipation

38
Q

What are the clinical features of myotonic dystrophy?

A 
Myotonia
Weakness
Cataracts
Ptosis
Frontal balding
Cardiac defects
39
Q

Describe muscular dystrophies

A 
Inherited
Non-inflammatory
Progressive
No central or peripheral nerve abnormality 
Duchenne/Becker most common
40
Q

What are some infective muscular diseases?

A

Viral- Coxsacchie
Trypanosomiasis
Cistercercosis- uncooked pork
Borrelia

41
Q

What is rhabdomyolysis?

A

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

42
Q

What are the clinical features of rhabdomyolysis?

A

Myalgia, muscle weakness and myoglobinuria

Complications of acute renal failure and DIC

Neurology (27 decks)

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