A 23-year-old photographer begins to experience \'strange\' symptoms. She begins

Question

A 23-year-old photographer begins to experience 'strange' symptoms. She begins to experience eyestrain after reading for 15 minutes, she becomes tired after chewing her food, brushing her teeth, or even combing her hair. Her work as a photographer suffers because she is unable to carry her equipment She is evaluated by her physician, who suspects myasthenia gravis. While waiting for the results of a serum antibody test, the physician begins a treatment regimen using pyridostigmine, an acetylcholinesterase inhibitor. The woman immediately feels better and her strength returns. The results of the antibody test come in and the diagnosis of myasthenia gravis is confirmed. Use these results and your knowledge of the neuromuscular junction to answer the questions below. Given what you know about muscle neurotransmission, speculate as to the identity of the antibody (what is being bound?) Given the answers to 'a' combined with your knowledge of neuromuscular function, why would this person suffer from muscle weakness? Why would pyridostigmine, an acetylcholinesterase inhibitor, have a beneficial effect?

Explanation / Answer

a. The neuromuscular junction relies specifically on one type of neurotransmitter in order to transmit the electrical signal to the muscle fiber. The antibody would be one specific to that neurotransmitter, and would have a specific function in order to interfere with neurotransmitter function. b. Without the muscle receiving a signal through the neuromuscular junction pathway, how would it be able to contract, particularly in concert with those around it? c. Enzymes need a substrate upon which to act. If another substrate is available for the enzyme to bind to (particularly if it has a higher affinity with the enzyme), then the enzyme will not longer bind to it's original substrate

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