The Action Potential and Neuromuscular Junction Problem I: Linda was a bit nervo
ID: 3515730 • Letter: T
Question
The Action Potential and Neuromuscular Junction
Problem I:
Linda was a bit nervous going to the doctor’s office but she knew that she had to go because of the chronic fatigue she was experiencing. In addition, she was now starting to notice muscle weakness on her face as well as her left eyelid was drooping in the late afternoon. She simply couldn’t explain the symptoms away. Sitting in the doctor’s office waiting to be called, Linda thought she was being silly as she imagined it to be nothing more than taking too many courses in the semester. Still, there was that nagging concern in the back of her mind. Finally, the nurse called her back and took her vitals. Her BP was 118/69 and her weight was a reasonable 127 lbs for a 5’ 5” person. The doctor shows up in a few minutes and talks with Linda extensively about her symptoms. He suggests a single fiber electromyography. Linda leaves the office and takes the exam later at a nearby hospital. There are many possibilities the doctor is considering to explain the muscle weakness Linda is experiencing.
There are 3 mechanisms found just in the synapse that could explain Linda’s symptoms. Describe them and how they may relate to Linda’s issues.
1. (5 pts) Presynaptic action potential:
2. (5 pts) ACh quantity released:
3. (5 pts) Activity of Acetylcholinesterase: With the results in hand, the doctor meets with Linda again explains to her it is most likely myasthenia gravis (MG). He then prescribes neostigmine and asks Linda to return in 2 weeks for a follow up visit.
4. (10 pts) Describe how neostigmine works and how it may help Linda’s symptoms.
5. (10 pts) How would the botulinum toxin affect Linda’s disorder? Be thorough in your response.
Explanation / Answer
1. Presynaptic action potential
Answer- Action potentials commonly initiated by excitatory postsynaptic potentials from the presynaptic neuron. neurotransmitter molecules are released from the presynaptic neuron. These neurotransmitters bind to receptors on the postsynaptic neuron or muscle causing contraction.
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2. ACh quantity released
Answer- the ACh released during each action potential is not changed. the post-synaptic ACh receptors are affected causing not enough muscle contraction resulting in weakness and fatigue.
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3. Activity of Acetylcholinesterase
Answer- With the results in hand, the doctor meets with Linda again explains to her it is most likely myasthenia gravis (MG). He then prescribes neostigmine and asks Linda to return in 2 weeks for a follow-up visit.
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4. Describe how neostigmine works and how it may help Linda’s symptoms.
Answer- Neostigmine slows the breakdown of acetylcholine when it is released from nerve endings. so that the action of ACh on the available ACh receptors can be prolonged. causing prolonged or stronger muscle contraction.
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5. How would the botulinum toxin affect Linda’s disorder? Be thorough in your response.
Answer- Botulinum toxin is a neurotoxic protein produced by bacterium Clostridium botulinum. It prevents the release of the neurotransmitter ACh from the axon endings at the neuromuscular junction which causes flaccid paralysis. this can worsen Linda's disorder. it can also lead to bulbar paralysis affecting the respiratory muscles.
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