Defect in myasthenia gravis is at the level of?

Ans. a (Skeletal muscles). (Ref. Harrison, Principles of Medicine, 18th/Ch. 386)MYASTHENIA GRAVIS# MG is a neuromuscular disorder characterized by weakness and fatiguabilty of skeletal muscles. The underlying defect is decrease in the number of Ach receptors at NMJ due to cell mediated autoimmune attack.# In NMJ Ach is synthesized in motor nerve terminal and stored in vesicle. When action potential travels down the motor nerve and reaches nerve terminal, Ach is released and combines with Ach receptors on post synaptic folds. Further causing sodium channels to open, depolarisation to occur and cause muscle contraction.# In MG fundamental defect is decrease in number of Ach receptors at post-synaptic muscle membrane. The nerve terminal is normal in MG.# Apart from number of Ach receptor, simplified postsynaptic folds and widened synaptic space are the two other pathologies causing MG.