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Neuroscience > L42 Diseases of the NMJ and Motor Unit > Flashcards

L42 Diseases of the NMJ and Motor Unit Flashcards

1
Q

what describes muscle weakness that originates in the nervous pathway (motor neuron, axon or NMJ)?

A

neurogenic

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2
Q

what describes muscle weakness that originates in the muscle itself?

A

myogenic/myopathic

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3
Q

what are the sites of lesions in the motor units?

A 
soma
axon
schwann cell
nerve ending
synaptic cleft
end plate
muscle fiber
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4
Q

what can cause nerve cell lesions in the soma or axon?

A

diseases
toxins
drugs
trauma

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5
Q

what are the sx/sx of lesions of the nerve cell in soma or axon?

A
  • atrophy/weakness
  • fibrillations and fasciculations
  • muscle fiber replaced by fibrous CT
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6
Q

what are examples of diseases that can occur in the soma or axon?

A

Lou Gehrig’s disease (ALS)

poliomyelitis

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7
Q

what does poliomyelitis affect?

A

muscles and nerves - particularly motor neuron of the spinal cord ventral horn

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8
Q

how is poliomyelitis transmitted?

A

direct person to person contact through oral, nasal and anal secretions

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9
Q

where does poliomyelitis enter, proliferate and spread?

A

mouth and nose

throat and intestinal tract

vascular and lymph system

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10
Q

how effective is the polio vaccine?

A

90% effective

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11
Q

what can cause lesions of Schwann cells?

A

autoimmune disease

toxins

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12
Q

what are the sx/sx of lesions of Schwann cells?

A

demyelination

conduction slowing or block

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13
Q

what are toxins and diseases can effect the NMJ?

A 
botulism
alpha-latrotoxin
beta-bungarotoxin
curare
Lambert Eaton syndrome
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14
Q

what happens in botulism?

A

toxic protease of anerobic bacteria inhibits ACh exocytosis = paralysis of all muscles

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15
Q

what are the 3 ways that botulism is spread

A

eating food that contains botulism toxin
infection of a wound with clostridium botulinum
consuming spores of clostridium botulinum

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16
Q

what happens with alpha-latrotoxin

A

black widow spider makes a neurotoxic venom
which causes a huge release of ACh
venom acts at nerve endings = tetanus and eventual paralysis

the venom reaches blood and lymph

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17
Q

what happens with beta-bungarotoxin?

A

snake venom toxin inhibits ACh exocytosis

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18
Q

what happens with curare (tubocurarin)?

A

arrowhead poison found in plants
non-depolarizing muscle relaxant
blocks ACh receptors at NMJ = temporary paralysis

19
Q

what is Lambert Eaton syndrome (at the cellular level)

A

autoimmune disease against voltage-gated Ca2+ channels in motor neuron terminal which causes insufficient release of ACh at the synaptic cleft

20
Q

in Lambert eaton syndrome, continued contractions will cause an _____ in the [ACh] in the cleft until it reaches a concentration sufficient to elicit a proper contraction

A

increase

strength increases with repeats muscular contraction

21
Q

what is lambert eaton syndrome associated with?

A

oat cell carcinoma of the lung

22
Q

in lambert eaton syndrome, what are the physiological changes seen at the end plate?

A
  • reduced amplitude of EPP
  • many EPPs do NOT attain threshold in muscle fibers
  • amplitude of minEPP is unchanged
23
Q

what are signs of Lambert eaton syndrome?

A

strength increase with activity
decreased reflexes
waxing on EMG (little to big)

24
Q

what are possible treatment options for Lambert eaton syndrome?

A
  • remove tumor + immunosuppresents
  • do plasma exchange
  • calcium gloconate (enhance Ca2+ influx into nerve terminal)
  • 4-aminopyridine (block K+ channels, prolong presyn AP and improve NT release)
25
Q

what are examples of synaptic cleft impairments?

A

congenital myesthenias
myesthenia gravis
myotonia congenita

26
Q

what are the types of congenital myasthenias?

A
  • AChE deficiency
  • slow channel syndrome
  • other
27
Q

what happens in AChE deficiency (congenital myasthenias)?

A

EPP is large and long
single stimuli delivered at low freq = single motor twitch
high freq. motor stimuli = temporal summation of EPPs + depolarization block of muscle

28
Q

what happens in slow channel syndrome (congenital myasthenias)?

A

binding of ACh to nAChR = prolonged opening of ACh receptor channel

if the channel is open too long = prolonged depolarization = depolarization block

muscle weakness, rapid fatigue, progressive atrophy

29
Q

what are the other forms of congenital myasthenias?

A

abnormal binding of ACh to nAChR

very brief opening times of ACh-gated channels

30
Q

what happens with myasthenia gravis?

A

autoimmune antibodies bind to alpha subunits of nAChR which block ACh ability to bind to receptor

most commonly affects young women and older men

antibodies do not compete with ACh

weakness NOT associated with denervation

serum from pts with MG causes disease symptoms in animals…

31
Q

what are the structural changes that occur at the end plate due to myasthenia gravis?

A

fewer nAChR
wider cleft
smaller/shallow junctional folds

32
Q

what is myasthenia gravis sometimes associated with?

A

thymus tumors

33
Q

what are the symptoms of MG?

A

weakness of voluntary muscle which improves with rest and worsens with activity
difficulty swallowing(choking?)
diplopia (double vision)
ptosis
late day paralysis
myasthenic crisis - difficulty breathing = may be life threatening

34
Q

what are the signs associated with dx of MG?

A 
EMG waning pattern
Tensilon test (AChE) test +
35
Q

what are possible treatment options for MG?

A

neostigmine/pyridostigmine (AChE inhibitor)
prednisone (cortisone)
axathioprine/cyclosporine (immunosuppresents)
plasma exchange (temporary improvement)
thymectomy (remission?)

36
Q

describe myotonia congenita?

A

autosomal dominant
Cl- channels are decreased in number which causes slower muscle relaxation

Cl- channels usually reset Vm after an AP, thus without the proper amount will increase excitability (unopposed K+ = soon depo) and decrease relaxation

pt suffer from muscle stiffness and hypertrophy

37
Q

describe Duchenne’s MD?

A

x linked recessive
absense of Dystrophin
onset in early childhood
die of respiratory and/or cardiac failure

38
Q

what is LMN syndrome?

A

second order neurons are lost

39
Q

where are the possible lesions sites for LMN syndrome?

A

motor axon or soma in the spinal cord or brainstem (CNs)

40
Q

what are the causes of LMN syndrome?

A

viral infections - poliomyelitis
trauma
neurodegeneration

41
Q

what are the sx/sx of LMN syndrome?

A 
weakness/paralysis
loss of reflex
fasciculations
fibrillations
atrophy
42
Q

describe poliomyelitis

A

most cases affects the motor neurons in the ventral horn (but can affect the whole entire body)
severe cases cause permanent paralysis or death

43
Q

how is poliomyelitis transmitted?

A

person to person contact (nose, mouth, fecal)

44
Q

how is polio prevented?

A

vaccine

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