Generation of Nerve Action Potential Flashcards
what is an action potential?
electrical impulse transmitted by nerve or muscle cell
change in voltage that causes cell to go from negative resting state to pos. state for brief time
at rest the cell membrane is highly permeable to what ion
K+
at peak of action potential the cell membrane is highly permeable to what ion
Na+
resting membrane potential is close to the equilibrium potential for
K+
when is threshold reached?
membrane depolarized by some electrical, mechanical, or chemical stimulus that causes influx of + charged ions
what happens at threshold?
voltage gated Na+ are opened which leads to further depolarization of the membrane (more positive)
describe the rising phase
so the threshold is reached, which means voltage gated sodium channels are opened, as the cell lets in more sodium it gets more positively charged leading to more sodium voltage gated channels to open. positive feedback, and the cell continues to get more pos. charged from all the sodium entering
draw a graph of the resting level, threshold, rising phase, overshoot, peak, repolarization, hyperpolarization
pg 8
what is the overshoot phase
membrane potential is so depolarized it reverses (that is, if resting membrane potential is around -70, at overshoot phase it will be above 0 so MUCH more + charged)
at the overshoot phase the membrane is most permeable to
Na+
at the overshoot phase the cell approaches equilibrium potential for
Na+
what happens at the peak phase
Na+ permeability starts to decrease, voltage gated K+ have been opened and the permeability of K+ increases
what happens at repolarization phase
due to the K+ being opened the membrane gets more negative
K+ ions are leaving the cell
what happens at afterhyperpolarization phase
K+ channels stay open long enough for the membrane potential to go more negative than the resting membrane potential
gNa means
conductance of sodium
depolarization and rising phase of action potential can be attributed to what conductance
gNa
increase in Na+ conductance
repolarization phase can be attributed to what conductance
gNa and gK
decrease in Na conductance
increase in K conductance
the return to the resting membrane potential can be contributed to what conductace
gK
decrease in K conductance
draw a graph of membrane potential, Na+ conductance and K+ conductance
pg 18
what technique was used to measure the action potential conductances
voltage-clamp technique
what does the voltage clamp technique allow
can hold the membrane potential constant in muscle or nerve cell and measure the ionic current flowing across the membrane
What does TTX stand for
Tetrodotoxin
What does TEA stand for
tetraethylammonium
What is function of TTX (Tetrodotoxin) and why is this helpful regarding measuring conductance
blocks voltage dependent Na+ conductance (permeability)
If you block the Na+ conductance you remove that variable and can see the affect of K+ without Na+
What is the function of TEA (tetraethylammonium) and why is this helpful regarding measuring conductance?
blocks voltage- dependent K+ conductance (permeability).
if you block K+ conductance you remove that variable and can see the affect of Na+ without K+
draw the Na+ current if TEA is used
pg 21
draw the K+ current if TTX is used
pg 21
draw the sodium voltage gate at resting, activation, and inactivation state
pg 22
draw the potassium voltage gate at resting, activation, and inactivation state
pg 23
elecrotonic potential vs action potential
pg 3
Describe what is happening with the K+ and Na+ during resting, rising, peak, repolarization, hyperpolarization, and resting state
pg 24
name four properties of action potentials
o Propagated without decrement
o All-or-none response
o Voltage inactivation of the action potential
o Refractory periods
Describe the absolute refractory period
if another stimulus is given to the neuron during this period it will not lead to a second action potential
sodium channels cannot reopen
what is the benefit of the absolute refractory period
prevents AP from traveling backward along axon
limits rate of firing of AP
Draw on graph where the absolute and relative refactory periods are in relationship to the AP
pg 28
describe the relative refractory period
only some of the voltage gated sodium channels are available to open, if there is a very strong stimulus the n some of the sodium voltage gated channels will open and generate another action potential
what is accomodation
An increase in the threshold for an action potential that occurs in some neurons during a slowly developing or prolonged depolarization. The result is that only a few action potentials are generated during prolonged depolarization above the normal threshold level
the more negative you are the more polar you are - that is an increase in
membrane potential
hyperpolarization is an increase in
membrane potential
what does ttx do
voltage gated sodium channels blocked by the toxin
if pt has ttx will they get action potential
no
if just voltage gated postassium channels are on will there be action potential
no
just hyperpolarization
in the presence of TEA
prolonged action potential
b/c K+ voltage gated channels are blocked
what does TEA do
blocks K+ current
downward deflection ( when it goes downard on a current graph) what does that mean
downward current - Na enters cell during AP
hyperkaleima
chronic elevated potassium outside cell - so say it’s at 10.
extended period of time
what happens in hyperkalemia
gradietn for potassium to leave is reduced, takes longer to repolarize the membrane
voltage gated sodium channel gets stuck in activated state so you can’t recruit another AP
get depolarization and get AP and then you won’t be able to generate another AP. this is why you have muscle weakness
succinylcholine
acts like or mimics hyperkalemia. potassium channel will stay open WHAT
what does refractory mean
can’t do anything
absolute refractory period ends in what phase
repolarization phase
what is happening that there can be strong signal and you can get AP during relative refractory period
sodium channels go back to rest
can there be AP when sodium channels are in inactivation state
no that is during absolute refractory period
the farther you are from the initial AP, what happens regarding refractory period and sodium voltage gated channels
the farther you are from initial AP, the more sodium will be at resting (instead of in inactivation phase), and the mores sodium that are at resting the lower the threshold and the bigger the AP you can get, because then more Na channels will respond, so it’s easier to get them to respond (threshold) and they can respond greater making a bigger depolarization
