NROB60 FINAL NOTES STUDY
SET EXAM
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)
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:
- 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
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
-staying open longer is going ot cause more Na to come in
, -open at more negative potentials (therefore, can have AP occuring sooner)
delayed rectifier - Answer Potassium conductance serves to rectify or reset membrane
potential
Structure of voltage gated potassium channels - Answer four separate polypeptide
subunits joint to form a pore
absolute refractory period - Answer cannot fire an AP again
Na channels are inactive since the membrane is strongly depolarized
cannot be activated again and no further APs until the membrane potential goes
sufficiently negative to deinactivate the channels
Relative refractory period - Answer We could get an AP again but we need more of a
depolarizing current in order to bring it to threshold
Membrane potential stays hyperpolarized until VG K channels close
What is the propagation of action potentials influenced by? - Answer myelination
propagation in unmyelinated axons vs myelinated axons - Answer Propagation in
unmyelinated axon requires reproduction of the AP at each successive axonal segment
- slower
- Because we put in our stimulus and at each point along the axons → we have change
happening (from going from positive to negative)
Propagation in myelinated axons requires reproduction of the action potential in the
nodes of Ranvier
(SALTATORY CONDUCTION)
- this increases the speed of conduction
- we are not having change occur at EVERY SINGLE POINT in the axon
- AP regenerates at the nodes of ranvier
Orthodromic - Answer AP travels in one direction
- does not go backwards
Antidromic - Answer Backward propagation
What are the four factors that influence conduction velocity? - Answer spread of AP
along membrane (dependent upon axon structure)
path of positive charge (inside axon = faster, across the axonal membrane = slower)
SET EXAM
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)
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:
- 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
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
-staying open longer is going ot cause more Na to come in
, -open at more negative potentials (therefore, can have AP occuring sooner)
delayed rectifier - Answer Potassium conductance serves to rectify or reset membrane
potential
Structure of voltage gated potassium channels - Answer four separate polypeptide
subunits joint to form a pore
absolute refractory period - Answer cannot fire an AP again
Na channels are inactive since the membrane is strongly depolarized
cannot be activated again and no further APs until the membrane potential goes
sufficiently negative to deinactivate the channels
Relative refractory period - Answer We could get an AP again but we need more of a
depolarizing current in order to bring it to threshold
Membrane potential stays hyperpolarized until VG K channels close
What is the propagation of action potentials influenced by? - Answer myelination
propagation in unmyelinated axons vs myelinated axons - Answer Propagation in
unmyelinated axon requires reproduction of the AP at each successive axonal segment
- slower
- Because we put in our stimulus and at each point along the axons → we have change
happening (from going from positive to negative)
Propagation in myelinated axons requires reproduction of the action potential in the
nodes of Ranvier
(SALTATORY CONDUCTION)
- this increases the speed of conduction
- we are not having change occur at EVERY SINGLE POINT in the axon
- AP regenerates at the nodes of ranvier
Orthodromic - Answer AP travels in one direction
- does not go backwards
Antidromic - Answer Backward propagation
What are the four factors that influence conduction velocity? - Answer spread of AP
along membrane (dependent upon axon structure)
path of positive charge (inside axon = faster, across the axonal membrane = slower)
