Assignment
Going Under the Knife: A Case on Membrane Structure and Function
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 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?"
Task
A. At resting membrane potential, why does a small amount of sodium leak into the cell instead of out?
B. Define depolarization and hyperpolarization and their relationship to threshold.
C. Kevin is conscious when certain neurons in his brain are active-they depolarize and undergo action potentials. Describe the process of depolarization of a neuron to threshold.
D. What does Cole mean when he says that anesthesia "inhibits the neurons?"
E. Is Cole correct when he assumes that leak potassium channels are different than voltage-gated potassium channels? Explain your answer.
F. If the anesthesia opens more potassium leak channels, why are Kevin's neurons less likely to produce action potentials?
G. 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?
H. 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.