Going Under the Knife: A Case on Membrane Structure andFunction

Twenty-year-old Kevin groaned and clutched his abdomenas he lay on the emergency room gurney. He had just been diagnosedwith acute appendicitis and was waiting to be taken to theoperating room (OR). Although he desperately wanted the pain tostop, Kevin was terrified of having general anesthesia. He hopedhis fear wasn’t obvious to his older brother Cole, who wasfinishing medical school and thought he kneweverything.

“Hang in there,” Cole said, for what seemed like theeighteenth time. “I’m sure they’ll get you upstairs as soon as theycan. They don’t want that thing to burst.”

Kevin grunted. “I know…but does that anesthesia staffwork all the time? How can I not wake up when someone’s slicing mygut open?”

Cole assumed a professorial air, and Kevin wished he’dkept his mouth shut. However, Cole didn’t get a chance to sayanything before an aide arrived to take Kevin to theOR.

In the OR, someone placed a mask over Kevin’s face andwhen he blinked, he suddenly found himself in a hospital room withCole 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? Howdid I get here already?”

“You’ve been out for a few hours,” Cole chuckled andthen launched into the wonders of general anesthesia. “Certainneurons have to depolarize and undergo an action potential tomaintain consciousness, but some anesthetics can hyperpolarize themand produce unconsciousness. The anesthetic binds to and opens acertain kind of potassium channel, which increases the “leak”current of potassium. However, it doesn’t affect voltage-gatedpotassium channels. This inhibits the neurons, and therefore youaren’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’mjust glad the stuff worked. Now when can I go home?”

Short answer questions

1. Kevin is conscious when certain neurons in his brainare active—they depolarize and undergo action potentials. Describethe process of depolarization of a neuron tothreshold.

2. What does Cole mean when he says that anesthesia“inhibits the neurons?”

3. If the anesthesia opens more potassium leak channels,why are Kevin’s neurons less likely to produce actionpotentials?

4. Suppose Kevin’s pre-op blood work indicates that hisextracellular potassium concentration is much higher than usual.This condition is known as hyperkalemia and must be correctedbefore he can undergo surgery. One of the dangers of hyperkalemiais that it makes neurons and muscle cells more excitable. Why doeselevated extracellular potassium have this effect?