Suppose Kevin’s pre-op blood work indicates that his extracellular potassium concentration is much higher than usual. This condition is known as hyperkalemia and must be corrected before he can undergo surgery. One of the dangers of hyperkalemia is that it makes neurons and muscle cells more excitable. Why does elevated extracellular potassium have this effect? 2. Similar types of potassium channels are found in skeletal muscle cell (plasma) membranes. Predict the effect of general anesthesia on Kevin’s skeletal muscle contraction during surgery.
Twenty-year-old Kevin groaned and clutched his abdomen as he lay on the emergency
room gurney. He had just been diagnosed with acute appendicitis and was waiting to be
taken to the operating room (OR). Although he desperately wanted the pain to stop,
Kevin was terrified of having general anesthesia. He hoped his fear wasn’t obvious to his
older brother Cole, who was finishing medical school and thought he knew everything.
“Hang in there,
” Cole said, for what seemed like the eighteenth time. “I’m sure they’ll get
you upstairs as soon as they can. They don’t want that thing to burst.”
Kevin grunted. “I know…but does that anesthesia stuff work all the time? How can I not
wake up when someone’s slicing my gut open?”
Cole assumed a professorial air, and Kevin wished he’d kept his mouth shut. However,
Cole didn’t get a chance to say anything before an aide arrived to take Kevin to the OR.
In the OR, someone placed a mask over Kevin’s face and when he blinked, he suddenly
found himself in a hospital room with Cole waiting in a chair by the bed. “Welcome back
to consciousness, little brother. How’s your abdomen feel?”
Kevin frowned. “Not as bad as it did. So it’s over? How did I get here already?”
“You’ve been out for a few hours,
” Cole chuckled, and then launched into the wonders of
general anesthesia. “Certain neurons have to depolarize and undergo an action potential
to maintain consciousness, but some anesthetics can hyperpolarize them and produce
unconsciousness. The anesthetic binds to and opens a certain kind of potassium channel,
which increases the “leak” current of potassium. However, it doesn’t affect the voltage-gated potassium channels. This inhibits the neurons, and therefore you aren’t conscious
of the surgeons performing the procedure. Amazing!”
Kevin groaned again, but not from the pain this time. Cole was undoubtedly right but he
sounded like a textbook. “I’m just glad the stuff worked. Now when can I go home?”
Short answer questions
1. Suppose Kevin’s pre-op blood work indicates that his extracellular potassium
concentration is much higher than usual. This condition is known as hyperkalemia
and must be corrected before he can undergo surgery. One of the dangers of
hyperkalemia is that it makes neurons and muscle cells more excitable. Why does
elevated extracellular potassium have this effect?
2. Similar types of potassium channels are found in skeletal muscle cell (plasma)
membranes. Predict the effect of general anesthesia on Kevin’s skeletal muscle
contraction during surgery.
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