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Harrison's Principles of Internal Medicine, 18e
| Part 17. Neurologic Disorders > Section 3. Nerve and Muscle Disorders > |
Chapter 386. Myasthenia Gravis and Other Diseases of the Neuromuscular Junction
Sections: Myasthenia Gravis and Other Diseases of the Neuromuscular Junction: Introduction, Diagnosis and Evaluation, Further Readings.
Topics Discussed: myasthenia gravis; neuromuscular junction diseases.
Excerpt:"Myasthenia gravis (MG) is a neuromuscular disorder characterized by weakness and fatigability of skeletal muscles. The underlying defect is a decrease in the number of available acetylcholine receptors (AChRs) at neuromuscular junctions due to an antibody-mediated autoimmune attack. Treatment now available for MG is highly effective, although a specific cure has remained elusive.At the neuromuscular junction (Fig. 386-1), acetylcholine (ACh) is synthesized in the motor nerve terminal and stored in vesicles (quanta). When an action potential travels down a motor nerve and reaches the nerve terminal, ACh from 150 to 200 vesicles is released and combines with AChRs that are densely packed at the peaks of postsynaptic folds. The structure of the AChR has been fully elucidated; it consists of five subunits (2 , 1 , 1 , and 1 or  ) arranged around a central pore. When ACh combines with the binding sites on the subunits of the AChR, the channel in the..."
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