Flashcards in NMJ and muscle pathologies Deck (51)
Symptoms of LMN disorders?
What innervated skeletal muscle fibres?
Motor neurones whose cell bodies arise in the ventral horn of the spinal cord
What is the motor end plate?
Synapses formed between motor neurons and the muscle
What is a motor unit?
A single motor neurone and all of the muscle fibres it innervates
What occurs when an action potential reaches the nerve?
Ca 2+ channels open
Vesicles of ACh are released into the synaptic cleft
ACh receptor opens and renders the membrane permeable to Na/K+ ions
Depolarisation starts an action potential at the motor end plate
What is the action of acetylcholinesterase?
Breaks up ACh into acetate and choline
What happens to choline in the synaptic cleft?
Sequestered into presynaptic vesicles
How does botulism affect the presynaptic membrane?
Cleaves presynaptic proteins involved in vesicle formation and blocks vesicle docking with the presynaptic membrane
What are the symptoms of botulism toxin?
Rapid onset weakness WITHOUT sensory loss
What is the pathogenesis of Lambert Eaton Myasthenic Syndrome?
Antibodies to presynaptic calcium channels leading to vesicle release
Strong assoc with small cell lung carcinoma
What is the treatment for LEMS?
What is the pathogenesis of myasthenia gravis?
Autoimmune antibodies to AChR resulting a reduced number of functioning receptors leading to muscle weakness and fatigability
Flattening of endplate folds
Even with normal ACh; transmission becomes inefficient
What is the role of the thymus in myasthenia?
75% have hyperplasia or thymoma
What is the epidemiology of myasthenia gravis?
Occurs at any age; 2 peaks of incidence
Females in 3rd decade
Males in 6/7th decade
Female:male ration 3:2
What are the clinical features of myasthenia?
Fluctuating weakness throughout the day; tends to be best in the morning
Facial and bulbar weakness
Limb weakness is proximal
What is the treatment for myasthenia?
Acetylcholinesterase inhibitor; pyridostigmine
IVIg in acute emergencies
What immune modulating drugs are used in myasthenia?
Emergency; plasma exchange or immunoglobulin
What drug should be avoided in myasthenia?
Lots of antibiotics CI, lots of anaesthetic drugs are CI
What do most people with myasthenia die from?
Immunosuppression SE in the elderly
What are the different types of muscle fibres?
Type 1; slow oxidative; resist fatigue, myoglobin, RED
Type 2a; fast oxidative; aerobic metabolism
Type 2b; fast glycolytic, easily fatigued
What is a fasciculation?
Visible, fast, fine, spontaneous twitch
Why do fasciculations occur?
Healthy muscle; stress, caffeine, fatigue
Denervated muscle which becomes hyperexcitable
What are fasciculations a sign of?
What is myotonia?
Failure of muscle relaxation after use
Chloride channel issues
What are the Si/Sy of muscle disease?
What can cause a head drop?
What muscles are commonly weak in muscle disease?
What are immune mediated muscle weaknesses?
What are inherited muscle disorders?
Limb girdle muscular dystrophies