A blockade of voltage sensitive na channels b

A) Blockade of voltage-sensitive Na+ channels
•
B) Blockade of voltage-sensitive K+ channels
•
C) Blockade of Na-K “leak” channels
•
D) Replacement of the voltage-sensitive K+ channels with
“slow” Ca++ channels
•
E) Replacement of the voltage-sensitive Na+ channels with
“slow” Ca++ channels

51.
Trace A represents a typical action potential recorded under
control conditions from a normal nerve cell in response to a
depolarizing stimulus. Which of the following perturbations
would explain the conversion of the response shown in trace A
to the action potential shown in trace B?
A) Blockade of voltage-sensitive Na+ channels
•
B) Blockade of voltage-sensitive K+ channels
•
C) Blockade of Na-K “leak” channels
•
D) Replacement of the voltage-sensitive K+ channels with
“slow” Ca++ channels
•
E) Replacement of the voltage-sensitive Na+ channels with
“slow” Ca++ Channels X

These so-called slow Ca++ channels have a slower inactivation rate,
thereby lengthening the time during which they are open. This, in
turn, delays the repolarization phase of the action potential,
creating a “plateau” before the channels inactivate.

52.
Which of the following perturbations would account for
the failure of the same stimulus to elicit an action
potential in trace C?
•
A) Blockade of voltage-sensitive Na+ channels
•
B) Blockade of voltage-sensitive K+ channels
•
C) Blockade of Na-K “leak” channels
•
D) Replacement of the voltage-sensitive K+ channels
with “slow” Ca++ channels
•
E) Replacement of the voltage-sensitive Na+ channels
with “slow” Ca++ channels

52.
Which of the following perturbations would account for
the failure of the same stimulus to elicit an action
potential in trace C?
•
A) Blockade of voltage-sensitive Na+ channels X
•
B) Blockade of voltage-sensitive K+ channels
•
C) Blockade of Na-K “leak” channels
•
D) Replacement of the voltage-sensitive K+ channels
with “slow” Ca++ channels
•
E) Replacement of the voltage-sensitive Na+ channels
with “slow” Ca++ channels

53.
A 17-year-old soccer player suffered a fracture to the left tibia.
After her lower leg has been in a cast for 8 weeks, she is
surprised to find that the left gastrocnemius muscle is
significantly smaller in circumference than it was before the
fracture. What is the most likely explanation?
•
A) Decrease in the number of individual muscle fibers in the
left gastrocnemius
•
B) Decrease in blood flow to the muscle caused by
constriction from the cast
•
C) Temporary reduction in actin and myosin protein synthesis
•
D) Increase in glycolytic activity in the affected muscle
•
E) Progressive denervation

53.
A 17-year-old soccer player suffered a fracture to the left tibia. After
her lower leg has been in a cast for 8 weeks, she is surprised to find
that the left gastrocnemius muscle is significantly smaller in
circumference than it was before the fracture. What is the most likely
explanation?