3. Go back to the fl ow diagram, look at each stage, and predict where the antib

Question

3. Go back to the fl ow diagram, look at each stage, and predict where the antibodies in Annie’s blood could act to decrease synaptic function at the neuromuscular junction.

4. Neostigmine is one drug that may be prescribed for people with myasthenia gravis. This drug, like the edrophonium chloride injection, will make Annie feel stronger. Go back to the flow diagram, look at each stage, and determine how these drugs could work to increase synaptic performance.

5. In the absence of treatment, what has happened to the amplitude of Annie’s endplate potentials as her disease has progressed?

6. Can you account for her progressive weakness?

The Neuromuscular Junction An action potential enters the presynaptic terminal Voltage-gated channels open and &ions; enter the presynaptic terminal ons cause to fuse with the presynaptic membrane is liberated into the synaptic cleft The neurotransmitter reacts with on the muscle membrane Channels open and the muscle membrane The neurotransmitter is broken down by in the synaptic cleft This produces an IS taken up into the presynaptic cell in the muscle membrane

Explanation / Answer

3.The antibodies in Annie’s blood could act to decrease synaptic function when the neurotransmitter reacts with ACh receptor on the muscle membrane.

4.Neostigmine blocks the active site of acetylcholinesterase so that the enzyme can no longer break down the acetylcholine molecules before they reach the postsynaptic membrane receptors. This allows the threshold to be reached so a new impulse can be triggered in the next neuron. In myasthenia gravis there are not many acetylcholine receptors so with the acetylcholinesterase blocked, acetylcholine can connect to the few receptors and trigger a muscular contraction causing muscle fatigue.

5.The amplitude of Annie’s EPP’s has decreased because her neuromuscular junction is no longer receiving signals from her brain due to her EPP’s failing.

6.Muscles become progressively weaker during her activities, like swimming. Then when she rests they improve and the cycle goes on and on.

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