Neuromuscular junction and muscle conditions Flashcards
What is the motor end plate?
The synapse formed between the motor neurone and muscle
What is curare and how does it work?
A paralysing poison - occupies the acetyl choline receptor but does not trigger ion response, blocking the action potential at the synapse
How does botulinum cause paralysis?
Botulinum toxin cleaves presynaptic proteins involved in vesicle formation and block vesicle merging with the presynaptic membrane
What causes Lambert Eaton myaesthenic syndrome?
There are antibodies to presynaptic calcium channels, causing fewer ACh vesicles to release
What underlying pathology is Lambert Eaton syndrome associated with?
Small cell carcinoma
What is the most common disorder of the neuromuscular junction?
Myasthenia gravis
What causes myasthenia gravis?
Autoimmune - antibodies to the ACh receptor on the post synaptic junction
What are the symptoms of myasthenia gravis?
Muscle weakness and fatiguability
Droopy eye lids
Double vision
When in the disease do symptoms of myasthenia gravis start to show?
When ACh receptors have been reduced to 30%
What effect do the ACh antibodies of myasthenia gravis have on the neuromuscular junction?
Block binding of ACh
Cause end plate flattening
Trigger inflammatory cascade, damaging the folds of the postsynaptic membrane
What role does the thymus play in myasthenia gravis?
75% patients have hyperplasia or thymoma
At what age does myasthenia gravis tend to occur?
Any age, but most common:
Females in 3rd decade
Males in 5th or 6th decade
Does limb weakness associated with myasthenia gravis tend to be distal or proximal?
Proximal
What is the treatment of myasthenia gravis?
Acetylcholinesterase inhibitor: pyridostigmine
Thymectomy
Immunomodulating drugs
Steroids/azothiaprine
Emergency: plasma exchange or immunoglobulin
What is a fasciculation?
Visibile, fast, fine, spontaneous twitch
