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Flashcards in Action Potential Deck (12)
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The sodium channels contribute to what phase of an action potential? What will happen if there is a reduction in external sodium?

The depolarizing phase. Smaller and slower action potentials.


Action potentials are generated by 3 different voltage-sensitive mechanisms, what are they?

1 activation of Na+ conductance.
2 delayed activation of K+ conductance
3 Inactivation of Na+ conductance


The undershoot of the membrane potential is due to what?

Open voltage gated K+ channels that gradually close.


Voltage clamps were used to test early squid axons and discover changes in Na+ and K+ conductances. What do they allow to be measured?

Mesure of the current flowing across the membrane. The amount of current that must be injected by the voltage clamp to keep the membrane voltage constant equals that value.


For K+ and Na+, which is the early inward current and which is the late outward current?

Na+ early inward.
K+ late outward.


Tetrodotoxin (TTX, from a puffer fish) blocks what type of channel? Does it affect the other type?

Na+ channels. No, K+ is not effected.


Tetaethylammonium bromide (TEA) blocks what type of channel? Does it affect the other type?

Block K+. Does not affect Na+. It is also an ACh receptor blocker.


The AP requires active and passive flow. What are these types of flow?

Active flow- the gating of the voltage-gated channels and associated influx of Na+ current.
Passive flow- Depolarization wave that precedes the action potential.


The absolute refractory period is equivalent to? What limit does this have?

The Na+ channel inactivation. It limits the frequency of firing.


What is the order of the 4 different voltage-sensitive mechanisms of an AP?

1 - activation of Na+ conductance
2 - activation of K+ conductance
3 - Inactivation of Na+ conductance
4 - closing of voltage gated K+ channels


Oligodendrocytes in the CNS and Schwan cells in the PNS are glial cells that wrap their membranes around the axon. What effect does this have on capacitance?

It decreases capacitance since C = sum of A/ d.
It also increases insulation and reduces leak of passive flow.


What effect does Multiple Sclerosis have on nerve fibers?

It demyelinates them disrupting saltatory conduction slowing and even blocking the transmission of nerve impulses in the CNS. Demyelination increases the capacitance of the membrane.