Muscle Problems Flashcards
Where do motor neurons cell bodies arise from?
ventral horn of the spinal cord
What is the motor end plate?
the synapse between the muscle and the motor neurones
How many motor neurones does each muscle cell respond to?
ONE MOTOR NEURONE = ONE MUSCLE CELL
What is Curare?
a toxin that acts in the same position as Ach but does not open the channel
What does Curare lead to?
no muscle contraction = no respiration
Name 2 pre synaptic disorders?
Botulism
Lambert Eaton Myasthenic syndrome
What is Botulism?
rapid onset weakness WITHOUT SENSORY LOSS
What causes Botulism?
clostridium botulism - heroin is often contaminated with it, or it is found in soil
What is the action of botulism toxin to cause the problems?
cleaves pre synaptic proteins involved in vesicle formation and blocks vesicle docking with the presynaptic membrane
What is the presentation of Lambert Eaton syndrome?
very like Myasthenia gravis
weakness throughout the day
extraocular and facial weakness
What causes LES?
antibodies to presynaptic calcium channels leads to less vesicle release
strong association with underlying small cell carcinoma
What is the treatment for LES?
3-4diaminopyridine
What type of disorder is myasthenia gravis?
post synaptic disorder
What is the pathophysiology behind myasthenia gravis?
autoimmune disorder - antibodies to acetyl choline receptors
reduced number of receptors leads to muscle weakness and fatigue
What is the pathophysiology of myasthenia gravis?
reduced number of ACh receptros and flattening of end plate folds leads to inefficeint transmission of ACh
What is the epidemiology of myasthenia gravis?
females in 30s
males in 60-70s
females>males
What is the presentation of myasthenia gravis?
symptoms start when ACh receptros are reduced to 30% of normal
Ach antibodies are found in 80-90% of patients
weakness is typically worse throughout the day
extraocular weakness and facial and bulbar weakness
proximal limb weakness
75% of patients have thymus hyperplasia or thymoma
What is the acute treatment of myasthenia gravis?
aceytlcholinerase inhibitor - pyridostigmine
IV immunoglobulin - mops up antibodies
thymectomy - even in absence of thymus abnormality
What is the chronic treatment of myasthenia gravis?
immunomodulation
steroids and steroid sparing agents - azathioprine or mycophenolate
What must be avoided in myasthenia gravis and why?
gentamicin - precipitates it
What is the prognosis for those with myasthenia gravis?
mortality 3-4%, usually from respiratory failure or aspiration pneumonia
What are fasiculations?
visible, fast, spontaneous twitch in smooth muscle
normal in large muscles
abnormal in small muscles
indicates a deinnervated muscle has become overexcitable due to motor neurone disease
What is myotonia?
failure of muscle relaxation after use
due to chloride channel abnormalities
What is the presentation of myotonic dystrophy?
myotonia weakness cataracts cardiac weakness/defects proximal weakness frontal balding
