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NROB60 FINAL NOTES Exam Questions With 100% Verified Answers Properties of the action potential - answerrising phase overshoot falling phase undershoot What happens when the current reaches threshold? - answergenerate APs at a low rate What happens when current increase? - answerrate of AP g...

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  • 1 oktober 2024
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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

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