Download Case Study in Muscle Physiology

Case Study in Muscle Physiology
“It’s Like Pulling Teeth”
Part I—The Hospital
At last the day had come. Mr. Thompson was having his wisdom teeth removed. He was
tired of the aches and pains and the sight of his puffy face in the mirror every morning.
He felt helpless, lying on the gurney watching the ceiling lights whiz by as he was being
wheeled to surgery.
Mr. Thompson had selected this particular oral surgeon because of the sign outside his
practice that read: “We cater to cowards.” But the surgeon still hadn’t seemed to
understand Mr. Thompson’s fear of dental procedures; he had wanted to use a local
anesthetic. Fortunately, the anesthesiologist was sympathetic to his request for a general
anesthetic.
Then the halothane started to take effect and Mr. Thompson went under. Then, as surgery
was about to begin, Mr. Thompson started twitching. The anesthesiologist saw Mr.
Thompson’s heart rate increase a little, muscle contractions became strong and
widespread throughout his body, and the patient began to sweat profusely. As Mr.
Thompson’s temperature quickly increased, the anesthesiologist injected a solution into
the IV drip. Then Mr. Thompson went limp and all that could be heard was the sound of
oxygen rushing through the ventilator, assisting Mr. Thompson’s breathing.
“Next time we do as I say and we use a local,” muttered the angry surgeon as he glared at
Mr. Thompson.
Questions
1. In this case, why did Mr. Thompson’s body temperature rise? Where do you think
most of the heat is generated?
2. What chemical reactions in muscles use ATP and are therefore responsible for
generating the huge amount of heat?
3. If the oral surgeon had not injected something to make the contractions stop, what
would have happened to Mr. Thompson’s muscles? That is, what happens to
muscles that are continuously used at maximum force for extended periods?
Part II. Neuromuscular junction
Halothane clearly had an effect on Mr. Thompson’s skeletal motor system. Where in the process
could halothane act to produce strong and prolonged muscle contractions? You can determine the
location of this effect by looking at the normal function of motor nerves, chemical synapses, and
the muscles.
Fill out the chart below representing the steps that occur at the neuromuscular junction. Think
about what could go wrong at each step that would cause Mr. Thompson’s symptoms (what
would make a single action potential cause lasting muscular contractions?)
Part III. Muscle function
It turns out Halothane does not change the synaptic function at the neuromuscular junction; thus it
likely affects the muscles. Complete the flow diagram below by filling in the blanks
For each stage, think about see how halothane could alter muscle function so that a single action
potential would end up producing a prolonged maximal muscle contraction.
5. Decide (guess) which step (or steps) you think are the mostly likely to be affected by
halothane. Construct a hypothesis and state how the antidote would work.
Final questions:
6. Hypothetically, if sustained contractions in Mr. Thompson’s muscles were allowed
to continue (ignoring the health consequences), do you think this would cause a
change in the ratio of fiber types (fast, intermediate, slow) in his muscles? Why or
why not?
7. There is a disease called myasthenia gravis that causes the opposite problem as
Mr. Thompson. These patients have extreme muscle weakness and tire easily.
What might cause this disease, that is, what might cause an action potential in a
motor nerve not to be transmitted properly?