Neuromuscular Disorders Flashcards
(29 cards)
What is the motor end plate?
The synapse formed between motor neurones and muscle
An AP causes calcium channels to open causing what to be released into the synaptic cleft?
Vesicles of ACh
When ACh diffuses across the synapse, the membrane becomes permeable to what?
Na/K ions
Depolarisation of the membrane of motor neurones causes what?
Action potential at motor end plate
What can be used to stop ACh travelling across the synaptic cleft?
Acetylcholinesterase
Give some presynaptic neuromuscular disorders
Botulism
Lambert Eaton Myasthenic Syndrome
What occurs in botulism?
The clostridium botulinum toxin cleaves presynaptic proteins involved in ACh vesicle formation
What occurs in LEMS?
Antibodies to presynaptic Ca channels are formed
LEMS is strongly associated with what?
Small cell carcinoma
What is the main postsynaptic disorder?
Myasthenia gravis
What occurs in myasthenia gravis?
Antibodies to acetyl choline receptors (AChR) are formed
Symptoms of MG start when ACh receptors are reduced to what % of normal?
30%
What is main test used for MG?
Test for anti-AChR
What structure is commonly affected in MG?
Thymus
Give some clinical features of MG
Extraocular/facial/bulbar weakness
Proximal limb weakness
What is the acute treatment for MG?
AChesterase inhibitor (pyridostigmine)
IV immunoglobulin
Thymectomy
What is the general treatment of MG?
Immunomodulating
Steroids (prednisolone)
Steroid-sparing agents (azathioprine)
What drug must be avoided in MG?
Gentamicin
What is the smallest contractile unit of skeletal muscle?
Muscle fibre
What are fascicles formed from?
Muscle fibres surrounded by thin layer endomysium
What are fasciculations?
Visible fast spontaneous twitches of muscle
When can fasciculations occur pathologically?
Denervated muscle which becomes hyperexcitable
What is myotonia?
The failure of muscle relaxation after use
How does inclusion body myositis present?
Slowly progressive proximal weakness with thumb sparing
