Action Potentials Flashcards Preview

M2M Block Cards AJS > Action Potentials > Flashcards

Flashcards in Action Potentials Deck (15)

Define the threshold for an action potential.

The point at which sodium and potassium currents are exactly equal and opposite. (Na influx = K efflux)


What are the letter abbreviations for the two gates on the NaV channel?

m = activation gate (extracellular side)
h = inactivation gate (cytoplasmic)


What is the resting position of the gates of NaV?

m gate = closed
h gate = open


What is the resting position of the KV gate?

k gate = closed


What is the position of all three gates during depolarization (upward slope of AP)

all gates are open (m, h, k)


What is the position of all three gates during repolarization (downward slope of AP?)

m gate = open
h gate = closed
k gate = open


What is the position of all three gates during hyper-repolarization?

m gate = closed
h gate = closed
k gate = open


To what is the refractory period due? (2)

1. h gate remains closed (inactivation - takes time to reopen)
2. k gate remains open (again, takes time to close)


What are the two subdivisions of the refractory period?

Absolute (impossible to have another AP)
Relative (difficult b/c KV remains open, must have stronger impulse to make Na influx = K efflux


There exists a second gate in the sodium channel, which we will call the inactivation, or h gate, which is _____ at rest, and closes upon ______.

open; depolarization


When the membrane is depolarized, the activation gate ___ and the inactivation gate ____.

opens; closes


The activation gate swings ____- than the inactivation gate, so that when the axon is first depolarized there is a brief instant when both gates are open and sodium can then rush into the cell.



The K+ channel gates are ____ at rest, and ____ in response to depolarization.

closed; open


What is the positive feedback regulation of the NaV channels?

Once threshold is exceeded, a miniature ‘explosion’ occurs. Remember, at threshold, not all sodium channels are conducting yet. But the sodium entering the channels that are conducting will depolarize the membrane further, and that depolarization will cause more sodium channels to start conducting, which will cause more sodium entry, which will cause more channels to open.... This is called ‘positive feedback.’ In a few tens of microseconds, the sodium channels are all open, and Vm is well on its way to ENa..


What properties of nerves make APs necessary (3)?

Essentially, nerves are terrible conductors. Impulses can't be propagated more than ~1mm. There are three reasons:

1. Internal resistance is high (Ri)
2. Membrane resistance is low (Rm)
3. Membrane capacitance is high (Cm)

This means that signal "leaks" through the membrane and is transmitted slowly through the axon.