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NB1 > Diseases Of NMJ > Flashcards

Diseases Of NMJ Flashcards

1
Q

What is the motor unit?

A

• Alpha motor neuron plus all of the extrafusal fibers that it innervates

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2
Q

What are the neurogenic motor unit diseases?

A 
– Diseases of the peripheral nerve
– Lesions of:
•Cell body
•Axon
•Neuromuscular junction •Schwann Cells
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3
Q

What are myogenic NMJ diseases?

A

– Diseases of the muscle (myopathies)

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4
Q

What NMJ diseasesimpact the soma?

A

Lou Gehrig’s disease (ALS)

Poliomyelitis

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5
Q

What diseases effect Schwann cells?

A

Guillain-Barre

Diphtheria

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6
Q

What are the diseases affecting the nerve endings of the NMJ?

A

Botulism
Alpha-Latrotoxin
Beta-Bungarotoxin
Curare

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7
Q

What NMJ diseases impact the end plate?

A

Myasthenia gravis

nACHR defects

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8
Q

What NMJ diseases impact the synaptic cleft?

A

Myasthenias

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9
Q

What NMJ diseases impact the muscle fiber?

A

Myotonias

Muscular dystrophy

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10
Q

What are the etiology of nerve (soma and/or axon)?

A 
Etiology 
– Toxins
– Drugs
– Trauma
– Idiopathic 
– Pathogens

Soma

  1. Lou Gehrig’s Disease (ALS)
  2. Poliomyelitis
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11
Q

What are the manifestations of lesions of nerve (doma and/of axom)?

A

Manifestations:
– Muscle atrophy and weakness
– Hyporeflexia
– Fasciculations and fibrillations

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12
Q

What is polymyelitis?

A

Polio - polios “grey”
Myelitis - myelos “marrow” + -itis “inflammation.“
Infection causing inflammation of the gray matter in the spinal cord leading to paralysis.

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13
Q

What us the etiology of poliomyelitis?

A

Etiology
• Small RNA viruses of the Enterovirus genus of the Picornaviridae family.
• Transmission is via fecal-oral route.

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14
Q

What are the clinical features of the poliomyelitis?

A
  • Paralytic poliomyelitis: Profound asymmetrical muscle weakness and signs of LMN lesion
  • Extensive paralysis of the trunk may occur

• Mid-cervical involvement (C3-4-5) can paralyze diaphragm,
necessitating ventilation

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15
Q

What is the diagnosis of poliomyelitis?

A 
Clinical Features
Polymerase chain reaction (PCR) for detection of poliovirus
CSF
- Elevated WBC
- Mildly elevated protein
- Glucose is normal
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16
Q

What is the impact of Schwann cell lesions?

A

Lesions of Schwann Cells cause demyelination
- Conduction slowing or block

Schwann Cells
1. Guillain-Barre 2. Diphtheria

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17
Q

What is the etiology of Schwann cell lesions?

A

Etiology:
– Autoimmune attack
– Toxins

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18
Q

What is the alpha laatrotoxin?

A

Alpha-Latrotoxin
• Toxin in venom of the black widow spider that
causes massive release of ACh by affecting presynaptic exocytotic proteins

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19
Q

What is Beta-Bungarotoxin?

A

Beta-Bungarotoxin
• Toxin in venom of snake initially provokes
ACh release followed by ACh depletion by acting on proteins in nerve terminals involved in exocytosis

20
Q

What does the botulinum toxin do?

A

• BotulinumToxin
• Toxic anaerobic bacterial protease
that reduces ACh release by acting on presynaptic exocytotic proteins

21
Q

What does Curare do?

A
  • Curare(delta-tubocurarine)

* Blocks nAChRs

22
Q

What is lambert Eaton syndrome?

A

This is a presynaptic disorder of neuromuscular transmission in which release of acetylcholine (ACh) is affected

Autoimmune disease
– antibodies attack presynaptic voltage- gated calcium channels

23
Q

What does Lambert eaton syndrome affect?

A

Neuro-Muscular Junction

Lambert–Eaton Syndrome

24
Q

What are the charscteristics of lambert eaton syndrome?

A

– Muscle weakness and ‘facilitating neuromuscular
block’
– Often found in patients with pulmonary small cell
cancers

– Cell cultures express voltage-gated calcium channels
• Antibodiesmanufacturedagainsttheseproteins

– Antibodies cross-link voltage-gated calcium channels in
motor nerve terminals
• ReducedAChrelease

25
Q

What are the physiological changes at end plate in lambert eaton syndrome?

A

Physiological Changes at End Plate
– Amplitude of Mini EPP is unchanged
– Reduced amplitude of EPP

• Reduced quantal content
– Many EPPs do not attain threshold in muscle fibers
– Waxing response in EMG(relates to facilitating neuromuscular
block)

26
Q

Describe therapy of lambert eaton syndrome

A

Therapy for Lambert-Eaton Syndrome
– Removal of underlying tumor and immunosuppressive drugs

– Plasma exchange

– Calcium gluconate to enhance calcium influx into nerve terminal

– 4-aminopyridine (potassium channel blocker) to prolong presynaptic action potential and improve transmitter release

27
Q

What is congenital myasthenias?

A
  • Many forms of congenital Myasthenia

* They usually present at birth and show signs and symptoms before the age of two years

27
Q

What is congenital myasthenias?

A
  • Many forms of congenital Myasthenia

* They usually present at birth and show signs and symptoms before the age of two years

28
Q

What are the main forms of myasthenias?

A
  1. Deficiency of ACh-esterase in synaptic cleft at end plate
    – EPP amplitude is larger and more prolonged than normal
    – Motor nerve stimuli separated by long intervals cause single muscle twitches (indicating increased temporal summation)
    – Motor nerve stimuli delivered in trains produce temporal summation of EPPs and cause depolarization block of muscle
2. Prolonged opening of channels
• 'Slow Channel Syndrome'
– Inherited rare condition presents at birth or early childhood
• Muscle weakness
• Rapid fatigue
– Prolonged opening of the ACh channel
– A resultant depolarization block

Other forms
– One form where the binding of ACh to nAChR is abnormal
– One form where the ACh-gated channels have very brief opening times

29
Q

What is myasthenia gravis?

A

– Chronic autoimmune disease
• Antibodies to nAChRs develop and reduce transmission at the
NMJ

– Genetic susceptibility

30
Q

What are the symptoms of myasthenia gravis?

A

Symptoms
– Weakness of somatic muscles
• Not associated with denervation

– Fatigability
– Temporary restoration of strength after rest

31
Q

Describe antibody interactions

A

Interaction of Antibody and nAChR
– Antibodies bind to Alpha subunits of nAChR
– Antibodies do not compete with ACh for binding sites on subunits
– Antibodies cross-link neighboring nAChRs

32
Q

Explain the dynamics of cross-linked nAChRs in end plate membrane

A

Dynamics of cross-linked nAChRs in end plate membrane
– Endocytosis of nAChRs in end plate membranes
– Lysosomal destruction
– Enhanced removal rate of nAChRs but no enhanced rate of insertion of nAChRs into end plate membrane
– Fall of density of nAChRs at end plate

33
Q

What are the structural xhanges of the end plate?

A

Structional Changes at the End Plate – Fewer nAChRs
– Wider synaptic cleft
– Smaller junctional folds

34
Q

What are the clinical. Features of myasthenua gravis?

A

Clinical features:
– incidence 1:10,000
– xx : xy = 2:1 (all races), xx age 20-30 , xy age 60-70
– Typical onset: 1st symptom is diplopia in the afternoon, disappears following morning
– Gradual increase in duration of diplopia, followed by ptosis
– Restriction of extraocular movements
– Ptosis compensated by backward tilting of the head and
wrinkling of frontalis muscle

35
Q

How is Myasthenia Gravis diagnosed?

A

Diagnosis:
– Repeated clenching and unclenching of fist → rapid loss of strength

– Tensilon test (edrophonium): after injection of Tensilon (ACh- esterase inhibitor) muscular strength recovers temporarily

– Ice pack

– Anti- AChR antibody testing

– EMG

36
Q

What are the therapies of myasthenia Gravis?

A 
Therapies:
– Thymectomy
– Immunosuppressing medication: azathioprine,
corticosteroids
– Pyridostigmine (AChE inhibitor)

• Myasthenic crisis: medical emergency
– Causes: sudden onset of disease, patient becomes
refractory to drug
– ICU treatment, intubation and respirator therapy

37
Q

Describe myotonia congenita

A
  • Myotonia: delayed relaxation of muscle after voluntary contraction or percussion.
  • Myotonia congenita is due to a mutation in the ClCN1 chloride channel.
  • The chloride channel defect causes increased excitability
  • Muscular hypertrophy can develop despite little physical activity in these patients.
38
Q

What is myotonia congenita?

A

Smaller depolarization is required to evoke an action potential and may even cause a train of action potentials

Repetitive firing of the muscle fiber after motor nerve stimulation ceases
Delayed relaxation phase of the neuronal evoked muscular contraction

39
Q

What is muscular dystrophy?

A

MuscularDystrophy
Group of disorders that characteristics of progressive muscular
weakness

Duchenne Muscular Dystrophy
Most common X-linked recessive disorder of muscles
Onset in early childhood
Muscle weakness develops progressively
Patients die from cardiovascular and respiratory insufficiency Cause: absence of muscle protein - Dystrophin

40
Q

Describe the myopathy of muscular dystrophy

A

• Onset: 3–5 years of age
• Proximal muscle weakness and
calf hypertrophy is common

  • difficulty in running or getting up from the ground, frequent falls, or toe-walking
  • High serum marker levels of CK
41
Q

What are the lower motor neuron syndrome?

A

Lower Motor Neurons (LMNS) - primary motor neurons of the spinal cord and brain stem that directly innervate skeletal muscles.

• Upper Motor Neurons
-neurons that originate in higher regions of the brain (cortex…) and synapse on lower motor neurons.

42
Q

What are the signs of LMNS?

A 
Signs of LMNS
– Muscle weakness
(paresis)
– Flaccid paralysis
– Loss of tendon reflexes
– Fasciculations
– Fibrillations
– Developing muscle atrophy → death of muscle
43
Q

What are fasciculations and fibrillations in an LMNS?

A

Fasciculations and fibrillations are signs that muscle fibers are undergoing de-nervation.

• Fasciculations:
– Fasciculationsareirregularspontaneouscontractionsofthemuscle fibers in motor units giving visible twitches at surface of body. Fasciculations by themselves are not always a sign of motor neuron damage
https://www.youtube.com/watch?v=u421daHAgpY

• Fibrillations (EMG!)
– arespontaneouscontractionsofsinglemusclefibers.

44
Q

Describe the expression nAChRs in muscle

A

In embryonic muscle fiber the nAChRs are distributed across the entire surface

In adult muscle fiber the pattern of nerve stimulation leads to
aggregation of nAChRs under nerve endin

NB1 (67 decks)

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