PNB 2274 EXAM QUESTIONS AND
ANSWERS (GRADED A+)
The intracellular and extracellular concentrations are the same for cation A. The resting
membrane potential is -70mV. What is the net driving force for cation 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.
Given a typical neuron with ENA+ = +50mV and Vm = -70mV, determine the direction of
Na+ flow when the membrane is forcibly set to 0mV.
A) Flow out of the cell.
B) No net flow.
C) Flow inside the cell. - Answer- C) Flow inside the cell.
Given a typical neuron with ENA+ = +50mV and Vm = -70mV, determine the direction of
Na+ flow when the membrane is forcibly set to +120mV.
A) Flow out of the cell.
B) No net flow.
C) Flow inside the cell. - Answer- A) Flow out of the cell.
Given that Neuron X has equilibrium potential values of ENA = 50mv, EK = -90mV, and
ECl = -55mV, if Neuron X had a GNa that was 100x as large as either GK or GCl, what
would be the approximate value of the resting membrane potential (Vm)?
A) ~90mV
B) ~-55mV
C) ~50mV
D) Not enough information. - Answer- C) ~50mV
During lethal injection, K+ is added to the extracellular fluid. What would you predict the
resting membrane potential to be?
A) No change to the membrane potential
B) More hyperpolarized
C) More depolarized - Answer- C) More depolarized
During the falling phase of the action potential, the membrane hyperpolarizes beyond
the resting membrane voltage. The phenomenon is due to:
, A) A large number of open potassium channels.
B) A rapid influx of Sodium ions.
C) An influx of Calcium ions into the axon. - Answer- A) A large number of open
potassium channels.
When conductance is shown on the graph, why are both ionic traces positive?
Conversely, when ionic currents are shown, why is the [K+] ionic current trace positive
while the [Na+] ionic current trace is negative? - Answer- Both conductances are
positive because conductance of Na increases and then goes back to rest, so does K.
Conductance never becomes less than at rest. Ionic currents for sodium are positive
because it coming into the cell makes the current go negative. A positive ion such as K
going out of the cell causes a positive current.
What is the cause of the blip (?) in the [Na+] current trace? (Circled in purple in the
image above) - Answer- The blip is from ligand-gated channels closing, and it takes a
moment for the voltage-gated ones to open.
Check Answer
Review the data generated in your 3D graph. What is the maximum temperature (C) to
generate an action potential under the default cellular ion settings? What trends in the
action potential do you notice as the temperature begins to decrease? - Answer- 22
degrees C was the maximum temperature under which an action potential could form.
As the temperature decreased, the action potentials got wider and took longer to be
carried out. At higher temperatures, the action potential was sharp.
Referring to your hypothesis in Exercise 1, your simulation results in Exercise 2, and
your membrane drawing in Exercise 3, predict the mechanism of action of tetrodotoxin
(TTX) on a neuron. - Answer- TTX must block the voltage-gated sodium channels,
preventing an action potential from firing.
Which structure separates the right and left cerebral hemispheres?
A) Central sulcus
B) Lateral sulcus
C) Longitudinal fissure
D) Transverse fissure - Answer- C) Longitudinal fissure
Which structure is found on the frontal lobe?
A) Central sulcus
B) Lateral sulcus
C) Precentral gyrus
D) Postcentral gyrus - Answer- C) Precentral gyrus
Compare and contrast structures of the sheep and human brain as seen in the superior
view. Consider discussing size, shape, location, and visibility of each structure. (Refer to
the structure checklist for discussion ideas). - Answer- Sheep brain:
smaller, cerebellum is more posterior
ANSWERS (GRADED A+)
The intracellular and extracellular concentrations are the same for cation A. The resting
membrane potential is -70mV. What is the net driving force for cation 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.
Given a typical neuron with ENA+ = +50mV and Vm = -70mV, determine the direction of
Na+ flow when the membrane is forcibly set to 0mV.
A) Flow out of the cell.
B) No net flow.
C) Flow inside the cell. - Answer- C) Flow inside the cell.
Given a typical neuron with ENA+ = +50mV and Vm = -70mV, determine the direction of
Na+ flow when the membrane is forcibly set to +120mV.
A) Flow out of the cell.
B) No net flow.
C) Flow inside the cell. - Answer- A) Flow out of the cell.
Given that Neuron X has equilibrium potential values of ENA = 50mv, EK = -90mV, and
ECl = -55mV, if Neuron X had a GNa that was 100x as large as either GK or GCl, what
would be the approximate value of the resting membrane potential (Vm)?
A) ~90mV
B) ~-55mV
C) ~50mV
D) Not enough information. - Answer- C) ~50mV
During lethal injection, K+ is added to the extracellular fluid. What would you predict the
resting membrane potential to be?
A) No change to the membrane potential
B) More hyperpolarized
C) More depolarized - Answer- C) More depolarized
During the falling phase of the action potential, the membrane hyperpolarizes beyond
the resting membrane voltage. The phenomenon is due to:
, A) A large number of open potassium channels.
B) A rapid influx of Sodium ions.
C) An influx of Calcium ions into the axon. - Answer- A) A large number of open
potassium channels.
When conductance is shown on the graph, why are both ionic traces positive?
Conversely, when ionic currents are shown, why is the [K+] ionic current trace positive
while the [Na+] ionic current trace is negative? - Answer- Both conductances are
positive because conductance of Na increases and then goes back to rest, so does K.
Conductance never becomes less than at rest. Ionic currents for sodium are positive
because it coming into the cell makes the current go negative. A positive ion such as K
going out of the cell causes a positive current.
What is the cause of the blip (?) in the [Na+] current trace? (Circled in purple in the
image above) - Answer- The blip is from ligand-gated channels closing, and it takes a
moment for the voltage-gated ones to open.
Check Answer
Review the data generated in your 3D graph. What is the maximum temperature (C) to
generate an action potential under the default cellular ion settings? What trends in the
action potential do you notice as the temperature begins to decrease? - Answer- 22
degrees C was the maximum temperature under which an action potential could form.
As the temperature decreased, the action potentials got wider and took longer to be
carried out. At higher temperatures, the action potential was sharp.
Referring to your hypothesis in Exercise 1, your simulation results in Exercise 2, and
your membrane drawing in Exercise 3, predict the mechanism of action of tetrodotoxin
(TTX) on a neuron. - Answer- TTX must block the voltage-gated sodium channels,
preventing an action potential from firing.
Which structure separates the right and left cerebral hemispheres?
A) Central sulcus
B) Lateral sulcus
C) Longitudinal fissure
D) Transverse fissure - Answer- C) Longitudinal fissure
Which structure is found on the frontal lobe?
A) Central sulcus
B) Lateral sulcus
C) Precentral gyrus
D) Postcentral gyrus - Answer- C) Precentral gyrus
Compare and contrast structures of the sheep and human brain as seen in the superior
view. Consider discussing size, shape, location, and visibility of each structure. (Refer to
the structure checklist for discussion ideas). - Answer- Sheep brain:
smaller, cerebellum is more posterior
