PNB 2264 Practical II Questions with
100% Correct Answers
In frog muscle experiment, different motor units within the same muscle have:
A. The same threshold stimulus that will result in firing of an action potential that we
observed in lab
B. Different threshold stimulus that will result in firing of an action potential of different
amplitude that we observed in lab
C. The same threshold stimulus that will result in the same contractile force that we
observed in lab
D. Different threshold stimulus that will result in increasing contractile force that we
observed in lab - Answer- D. Different threshold stimulus that will result in increasing
contractile force that we observed in lab
Calibration of the force transducer is [X] (optional, required) after the frog muscle is
attached to it. After calibration, you should [Y] (leave, remove) the 5 g weight on/from
the transducer. - Answer- x- required
y- remove
As you increase voltage to the muscle, describe how it responds to the increased
stimulus. - Answer- as you inc stimulus voltage (mV) --> inc force (mN)
-due to recruitment of motor units
-stronger contraction
-higher amplitude
-up to a certain point- maximum excitation voltage
Given a typical neuron with ENa+ = +50mV and Vm = -70mV, determine the direction of
Na+ flow when the membrane is at +120 mV.
a. flow inside of the cell
b. flow outside of the cell
c. no net flow - Answer- b. flow outside of the cell
Given a typical neuron with EK+ = -90mV and Vm = -70mV, determine the direction of
K+ flow when the membrane is at 0 mV.
a. flow inside of the cell
b. flow outside of the cell
c. no net flow - Answer- b. flow outside of the cell
, Given a typical neuron with EK+ = -90mV and Vm = -70mV, determine the direction of
K+ flow when the membrane is at -90 mV.
a. flow inside of the cell
b. flow outside of the cell
c. no net flow - Answer- c. no net flow
Given that Neuron X has equilibrium potential values of ENa=50mv, EK = -90mV, and
ECl = -55mV, if neuron X had a GNa that was 100 times as large as either GK or GCl,
what would be the approximate value of the resting membrane potential (Vm)?
a. ~90 mV
b. ~55 mV
c. ~50 mV
d. not enough info to make the appropriate calculation - Answer- c. ~50 mV
During lethal injection, K+ is added to the extracellular fluid. What would you predict the
resting membrane potential?
a. no change in membrane potential
b. more hyperpolarized
c. more depolarized - Answer- c. more depolarized
The intracellular and extracellular concentrations are the same for cation A. The resting
membrane potential is -70mV. What is the net driving force for A during the resting
stage?
a. move from intracellular to extracellular
b. no net driving force
c. move from extracellular to intracellular - Answer- c. move from extracellular to
intracellular
A, B, and C are three cations. EA = 50 mV, EB = -50 mV, EC = -70 mV. If only the
channels for A and B are open. What is the membrane potential?
a. 50 mV
b. -50 mV
c. 0 mV
d. need more info - Answer- d. need more info
During the falling phase of the action potential, the membrane hyperpolarizes beyond
the resting membrane voltage. The phenomenon is due to:
a. a rapid influx of sodium ions
b. an influx of calcium ions into the axon
100% Correct Answers
In frog muscle experiment, different motor units within the same muscle have:
A. The same threshold stimulus that will result in firing of an action potential that we
observed in lab
B. Different threshold stimulus that will result in firing of an action potential of different
amplitude that we observed in lab
C. The same threshold stimulus that will result in the same contractile force that we
observed in lab
D. Different threshold stimulus that will result in increasing contractile force that we
observed in lab - Answer- D. Different threshold stimulus that will result in increasing
contractile force that we observed in lab
Calibration of the force transducer is [X] (optional, required) after the frog muscle is
attached to it. After calibration, you should [Y] (leave, remove) the 5 g weight on/from
the transducer. - Answer- x- required
y- remove
As you increase voltage to the muscle, describe how it responds to the increased
stimulus. - Answer- as you inc stimulus voltage (mV) --> inc force (mN)
-due to recruitment of motor units
-stronger contraction
-higher amplitude
-up to a certain point- maximum excitation voltage
Given a typical neuron with ENa+ = +50mV and Vm = -70mV, determine the direction of
Na+ flow when the membrane is at +120 mV.
a. flow inside of the cell
b. flow outside of the cell
c. no net flow - Answer- b. flow outside of the cell
Given a typical neuron with EK+ = -90mV and Vm = -70mV, determine the direction of
K+ flow when the membrane is at 0 mV.
a. flow inside of the cell
b. flow outside of the cell
c. no net flow - Answer- b. flow outside of the cell
, Given a typical neuron with EK+ = -90mV and Vm = -70mV, determine the direction of
K+ flow when the membrane is at -90 mV.
a. flow inside of the cell
b. flow outside of the cell
c. no net flow - Answer- c. no net flow
Given that Neuron X has equilibrium potential values of ENa=50mv, EK = -90mV, and
ECl = -55mV, if neuron X had a GNa that was 100 times as large as either GK or GCl,
what would be the approximate value of the resting membrane potential (Vm)?
a. ~90 mV
b. ~55 mV
c. ~50 mV
d. not enough info to make the appropriate calculation - Answer- c. ~50 mV
During lethal injection, K+ is added to the extracellular fluid. What would you predict the
resting membrane potential?
a. no change in membrane potential
b. more hyperpolarized
c. more depolarized - Answer- c. more depolarized
The intracellular and extracellular concentrations are the same for cation A. The resting
membrane potential is -70mV. What is the net driving force for A during the resting
stage?
a. move from intracellular to extracellular
b. no net driving force
c. move from extracellular to intracellular - Answer- c. move from extracellular to
intracellular
A, B, and C are three cations. EA = 50 mV, EB = -50 mV, EC = -70 mV. If only the
channels for A and B are open. What is the membrane potential?
a. 50 mV
b. -50 mV
c. 0 mV
d. need more info - Answer- d. need more info
During the falling phase of the action potential, the membrane hyperpolarizes beyond
the resting membrane voltage. The phenomenon is due to:
a. a rapid influx of sodium ions
b. an influx of calcium ions into the axon
