©BRAINBARTER 2024/2025
NROB60 FINAL NOTES Exam Questions
With 100% Verified Answers
Properties of the action potential - answer✔rising phase
overshoot
falling phase
undershoot
What happens when the current reaches threshold? - answer✔generate APs at a low rate
What happens when current increase? - answer✔rate of AP generation increases
increases the frequency of AP (all or none situation)
What does the firing frequency of APs reflect? - answer✔the magnitude of the DEPOLARIZING
current
(since hyperpolarizing would not allow threshold to be reached)
What is one way stimulation intensity is encoded? - answer✔firing frequency
What causes ionic changes? - answer✔depolarization causes increase in Na permeability by
opening gates in pores or ion channels
hyperpolarization - answer✔more negative
depolarization - answer✔more positive
what kind of current does the firing frequency reflect? - answer✔depolarizing current
(hyper polarization would not allow threshold to be reached)
, ©BRAINBARTER 2024/2025
How can you flip the membrane potential? - answer✔by changing the relative ionic permeability
of the membrane
rising phase --> have inward Na+ current
falling phase --> has outward K+ current
AP occurs during sudden shift in membrane properties
How does the permeability of the membrane change for AP? - answer✔membrane changes from
K permeability to Na permeability to K permeability
how are interneurons depolarized? - answer✔entry of Na+ through channels that are sensitive to
NT released by other neurons
What are the two types of channels? - answer✔voltage gated
ligand gated
Voltage gated channels - answer✔depends on a change in voltage in order to open and close
ligand gated channels - answer✔ex. needs a neurotransmitter in order to open/close
When is an AP generated? - answer✔if the depolarizing stimulus passes the threshol
Resting potential - answer✔only leak potassium channels are open (these are constantly in an
open state)
Rising Phase - answer✔more and more sodium channels open (driving force of sodium ions
rushing in)
entry of Na+ (usually because Na+ channels are sensitive to membrane stretching)
sodium influx
Overshoot phase - answer✔most positive state
two processes occur simultaneously:
, ©BRAINBARTER 2024/2025
- sodium gates begin to close
- K channels begin to open (these channels differ from leak potassium channels)
because the relative permeability of the membrane favours Na --> membrane potential
approached Ena which is GREATER than 0 mV
Falling phase - answer✔activation of voltage gated potassium channels are AT MAXIMUM
Na channels are mostly al closed
Potassium efflux
Undershoot phase - answer✔hyperpolarization occurs
membrane potential returns to normal
potassium channels (not LEAK ONES) close
little Na permeability and membrane approached Ek --> causes hyperpolarization relative to
RMP until the VG K channels close again
Which channel opens and closes faster? - answer✔Na
Structure of voltage gated sodium channel - answer✔one single long peptide with 4 distinct
domains
what does one domain of voltage gated sodium channel have? - answer✔6 transmembrane alpha
helices
pore loop --> where the ions can move across
Which alpha helix is the voltage sensor? - answer✔S4
consists of regularly spaced positively charged AAs
, ©BRAINBARTER 2024/2025
they react to changes in polarization of the membrane
- depolarization twists the S4 and this change in the molecule causes the gate to open
What makes the channel more permeable to Na+ ? - answer✔selectivity filter
selectivity filter - answer✔for Na channel:
- partially hydrated Na+ can fit through the pore but the partially hydrated K+ ion cannot since it
is TOO BIG
Functional properties of Na+ Channel - answer✔- threshold open up the sodium channel and
sodium can rush in
(open almost immediately)
- stays open for about 1msec then inactivates (Mg 2+ blocks it ) --> after Na+ rushes in
(this rapid opening of channels in response to depolarization explains the rising phase)
- cannot open again until voltage reduces to below threshold
- another AP cannot be generated until the channels are activated
Tetrodotoxin - answer✔could selectively block Na channel
clogs the Na permeable pore by binding tightly to a specific site on the OUTSIDE OF THE
CHANNEL
Saxitoxin - answer✔another Na+ channel blocking toxin
concentrated in clams, mussels, and other shellfish that feed on these organisms
marine protozoa
Batrachotoxin - answer✔- causes the channels to open at more negative potentials and to stay
open much longer than usual
NROB60 FINAL NOTES Exam Questions
With 100% Verified Answers
Properties of the action potential - answer✔rising phase
overshoot
falling phase
undershoot
What happens when the current reaches threshold? - answer✔generate APs at a low rate
What happens when current increase? - answer✔rate of AP generation increases
increases the frequency of AP (all or none situation)
What does the firing frequency of APs reflect? - answer✔the magnitude of the DEPOLARIZING
current
(since hyperpolarizing would not allow threshold to be reached)
What is one way stimulation intensity is encoded? - answer✔firing frequency
What causes ionic changes? - answer✔depolarization causes increase in Na permeability by
opening gates in pores or ion channels
hyperpolarization - answer✔more negative
depolarization - answer✔more positive
what kind of current does the firing frequency reflect? - answer✔depolarizing current
(hyper polarization would not allow threshold to be reached)
, ©BRAINBARTER 2024/2025
How can you flip the membrane potential? - answer✔by changing the relative ionic permeability
of the membrane
rising phase --> have inward Na+ current
falling phase --> has outward K+ current
AP occurs during sudden shift in membrane properties
How does the permeability of the membrane change for AP? - answer✔membrane changes from
K permeability to Na permeability to K permeability
how are interneurons depolarized? - answer✔entry of Na+ through channels that are sensitive to
NT released by other neurons
What are the two types of channels? - answer✔voltage gated
ligand gated
Voltage gated channels - answer✔depends on a change in voltage in order to open and close
ligand gated channels - answer✔ex. needs a neurotransmitter in order to open/close
When is an AP generated? - answer✔if the depolarizing stimulus passes the threshol
Resting potential - answer✔only leak potassium channels are open (these are constantly in an
open state)
Rising Phase - answer✔more and more sodium channels open (driving force of sodium ions
rushing in)
entry of Na+ (usually because Na+ channels are sensitive to membrane stretching)
sodium influx
Overshoot phase - answer✔most positive state
two processes occur simultaneously:
, ©BRAINBARTER 2024/2025
- sodium gates begin to close
- K channels begin to open (these channels differ from leak potassium channels)
because the relative permeability of the membrane favours Na --> membrane potential
approached Ena which is GREATER than 0 mV
Falling phase - answer✔activation of voltage gated potassium channels are AT MAXIMUM
Na channels are mostly al closed
Potassium efflux
Undershoot phase - answer✔hyperpolarization occurs
membrane potential returns to normal
potassium channels (not LEAK ONES) close
little Na permeability and membrane approached Ek --> causes hyperpolarization relative to
RMP until the VG K channels close again
Which channel opens and closes faster? - answer✔Na
Structure of voltage gated sodium channel - answer✔one single long peptide with 4 distinct
domains
what does one domain of voltage gated sodium channel have? - answer✔6 transmembrane alpha
helices
pore loop --> where the ions can move across
Which alpha helix is the voltage sensor? - answer✔S4
consists of regularly spaced positively charged AAs
, ©BRAINBARTER 2024/2025
they react to changes in polarization of the membrane
- depolarization twists the S4 and this change in the molecule causes the gate to open
What makes the channel more permeable to Na+ ? - answer✔selectivity filter
selectivity filter - answer✔for Na channel:
- partially hydrated Na+ can fit through the pore but the partially hydrated K+ ion cannot since it
is TOO BIG
Functional properties of Na+ Channel - answer✔- threshold open up the sodium channel and
sodium can rush in
(open almost immediately)
- stays open for about 1msec then inactivates (Mg 2+ blocks it ) --> after Na+ rushes in
(this rapid opening of channels in response to depolarization explains the rising phase)
- cannot open again until voltage reduces to below threshold
- another AP cannot be generated until the channels are activated
Tetrodotoxin - answer✔could selectively block Na channel
clogs the Na permeable pore by binding tightly to a specific site on the OUTSIDE OF THE
CHANNEL
Saxitoxin - answer✔another Na+ channel blocking toxin
concentrated in clams, mussels, and other shellfish that feed on these organisms
marine protozoa
Batrachotoxin - answer✔- causes the channels to open at more negative potentials and to stay
open much longer than usual
