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. What does Cole mean when he says that anesthesia “inhibits the neurons?”
2. Is Cole correct when he assumes that leak potassium channels are different than
voltage-gated potassium channels? Explain your answer.
3. If the anesthesia opens more potassium leak channels, why are Kevin’s neurons less
likely to produce action potentials?
4. 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?
5. 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.
check_circle
Expert Answer
thumb_up
thumb_down
Step 1
Anesthetic agents are administered to the patients before the surgery to induce unconsciousness in the
patient. They make the patient remains unresponsive so that the surgery can be carried out without any
interruption.
They are administered in the form of intravenous administration or via inhalation. Various anesthetic
agents are used for causing anesthesia. The anesthetic type is dependent on the type and duration of
the surgery.
Disclaimer: Since you have posted a question with multiple subparts, we will solve the first three
subparts for you. To get the remaining sub-part solved please repost the complete question and
mention the sub-parts to be solved.
Step 2
1. Anesthesia is the agent that alters the membrane potential of the neuron by increasing the negative
charge inside the neurons. When the membrane potential becomes more negative, then the threshold
for generating the action potential is never reached. It inhibits the firing of neurons from sending the
information to the brain.
2. Yes. The leak potassium channels are different from the voltage-gated potassium channels. The
voltage-gated potassium channels remain closed until the peak of the depolarization occurs. The
opening of the voltage-gated potassium channels helps the cell to return the membrane potential to the
resting condition.
The leak potassium channels are found across the neuron and are involved in regulating the resting
membrane potential. Not all the leak potassium channels are open at rest; Some remain open and some
remain closed. Opening of these leak potassium channels allows the movement of potassium (positive)
ions out of the cell, which alters the membrane potential.
Step 3
3. Opening more of the potassium leak channels tend to leak out the potassium ions out of the neuron
along its concentration gradient and makes the cell interior more negative and hyperpolarize the cell.
The action potential can be generated only when the membrane potential reaches its threshold. When
the threshold does not reach due to the leaking out of the potassium ions, then the generation of action
potentials is prevented.