The Tired Swimmer by Russo, Falk and Stephens

Part III—The Neurologist

Annie returned to the neurologist’s office with her mother. That morning Annie had been subjected to several different tests and she had been asked to return after lunch when the results would be in. The nurse told her that they were rushing this through because they knew that Annie was only home for a week. Annie and her mother sat in the waiting room for what seemed to be hours. At last the nurse came for them.

“Some of the results are here, and the rest are on their way,” she explained. “So the doctor will see you now.” Annie and her mother went into the doctor’s office and sat down.

“Well, Annie, I have read your family doctor’s notes, and we put you through a battery of tests this morning.”

The neurologist skimmed through the chart, “Hmm, blurred vision, weak fingers, and decline in swimming performance. OK, let’s see what we found out today. First, the nerve conduction and the electromyography (EMG) tests; these are the only results we have right now. This was the test when they put sticky electrodes on your skin, remember?”

Annie nodded.

“Well, for the nerve conduction tests one set of electrodes stimulated the nerve and another recorded its response a little way down the nerve. The nerve conduction results are normal. There is no nerve fatigue and the conduction velocity is fine; nothing wrong with your nerves.”

Annie and her mother looked at each other and smiled with relief.

“Now, the electromyography test involves recording from a muscle; it was done in two stages. The first stimulated the muscle directly, and there isn’t too much out of the ordinary there. The second stage is when the nerves were stimulated and the muscle response was recorded. These results concern me because the muscle response decreased quickly during repeated nerve stimulation, indicating that your muscle response fatigued over time.”

Figure 1.
(Click to enlarge)

Questions

According to the conduction test, was Annie’s nerve function normal?
According to Annie’s EMG test, was Annie’s skeletal muscle function normal?
Considering your answers to Questions 1 and 2, why did activity in Annie’s motor nerves produce a skeletal muscle response that fatigued during repetitive stimulation?
Fill in the blanks in the accompanying flow chart of the neuromuscular junction (Figure 1).
Now take each stage in turn and discuss how sustained neural activity could create a dysfunction and result in a decrease in muscle response during repetitive motor nerve stimulation.

Go to Part IV—“The Neurologist Continued”

Originally published at http://www.sciencecases.org/tired_swimmer/tired_swimmer3.asp