Neuromuscular Junction Flashcards
what is the motor end plate
synapses between motor neurons and muscles
what neurotransmitter is released from motor neurones
acetyl choline
what triggers release of acetyl choline from motor neurones
opening of voltage gated calcium channels (Ca influx)
effect of acetyl choline on muscle cells
makes the membrane permeable to Na/K ions starting action potential
effect of acetylcholinesterase
breaks down acetyl choline to acetate and choline
what is lambert eaton myasthenic syndrome
antibodies to presynaptic calcium channels
means less acetyl choline vesicle production and release
what condition is lambert eaton myasthenic syndrome strongly associated with
small cell carcinoma
what is the most common disorder of the neuromuscular junction
myasthenia gravis
what is myasthenia gravis
autoimmune antibodies to post-synaptic acetyl choline receptors
reduced numberof functioning receptors leading to muscle weakness and fatigue
Transmission improves with increased amount of acetyl choline in myasthenia gravis. True/false
False
even with normal amounts of Ach, transmission becomes ineffective
what organ plays a role in myasthenia gravis
thymus - 75% patients have hyperplasia or thymoma
clinical features of myasthenia gravis
fluctuating weakness - worse through the day
proximal limb weakness
most common presentation of mysasthenia gravis
extraocular, facial and bulbar weakness
treatment for myasthenia gravis
acetylcholinesterase inhibitor - pyridstigmine
thymectomy
immunomodulating
steroids/azathioprine
common causes of morbidity in myasthenia gravis
respiratory failure
aspiration pneumonia side effects from immunosuppression
what are clinical features of skeletal muscle disorders
proximal weakness - shoulder and hips
cant lift things/get out of chair
waddling gait - gower’s sign
LMN signs - weakness, wasting, hypoflexia, fasiculations
what trigger fasiculations
stress
caffeine
fatigue
what is myotonia
failure of muscle relaxation after use
causes of muscle problems
inflammatory - dermatomyositis
polymyositis
inherited - muscular dystrophies
congenital
polymyositis presentation
symmetrical progressive proximal weakness
what is raised in polymyositis
CK
what additional clinical feature is present in dermatomyositis
skin lesions
heliotrope rash on face
treatment for polymyositis/dermatomyositis
steroids
what is the most common muscular dystrophy
myotonic dystrophy
mode of inheritance of myotonic dystrophy
autosomal dominant - trinucleotide repeat disorder with anticipation
clinical features of myotonic dystrophy
myotonia weakness cataracts ptosis frontal balding cardiac defects
what conditions are mitochondrial disease associated with
deafness
diabetes
epilepsy
what drugs can cause muscular dystrophies
statins
anaesthetic agents
cocaine
GHB venoms
how does rhabdomyolysis cause muscular dystrophy
dissolution of muscle
leakage of toxic intracellular contents into plasma
clinical features of rhabdomyolysis
triad of:
myalgia
weakness
myoglobinuria (dark urine)
