Lecture 3 Flashcards
Voltage Gated Channels, Action Potentials, The Refractory Period, Current Underlying the AP,
The probability of the channel being
open is (equal/different) at each value of
membrane voltage
different
When there is low membrane potential, VG K+ channels are…
-closed/deactivated
-open/activated
closed/deactivated
When there is high membrane potential, VG K+ channels are…
-closed/deactivated
-open/activated
-open/activated
If activation and inactivation gates are open, VG Na+ channel is….
-open/activated
-inactivated
-closed/deactivated
-open/activated
If activation gate is open but inactivation gate is blocking the channel, VG Na+ channel is….
-open/activated
-inactivated
-closed/deactivated
-inactivated
If activation and inactivation gates are blocking the channel, VG Na+ channel is….
-open/activated
-inactivated
-closed/deactivated
-inactivated
If activation gate is blocking the channel but the inactivation gate is open, VG Na+ channel is….
-open/activated
-inactivated
-closed/deactivated
-closed/deactivated
VG Na+ channels have
-activation gates
-inactivation gates
-both
-none
both activation and inactivation gates
VG K+ channels have
-activation gates
-inactivation gates
-both
-none
activation gates
If the activation gate is open, VG Na+ and K+ channels are
-depolarized potential
-rest/hyperpolarized potential
-depolarized potential
If the activation gate is blocking the channels, VG Na+ and K+ channels are
-depolarized potential
-rest/hyperpolarized potential
-rest/hyperpolarized potential
Hyperpolarization is due to an (efflux/influx) of (K+/Na+), making the outside more positive.
Efflux of K+
Depolarization is due to an (efflux/influx) of (K+/Na+).
Influx of Na+
If [Na+]out is reduced, the overshoot of the action potential will (increase/decrease).
decrease
If [K+]out is increased, the undershoot of the action potential will (increase/decrease).
increase
The THRESHOLD for the AP firing is the membrane
potential:
– at which the Na+ influx…
– overcomes the K + efflux…
– resulting in an action potential (or more than one).
At the resting potential:
gK < gNa
gK = gNa
gK > gNa
gK > gNa – when only leak channels are open – more K leak channels
When the AP is rising:
gK < gNa
gK = gNa
gK > gNa
gK < gNa – VG Na channels open
When the Ap is falling:
gK < gNa
gK = gNa
gK > gNa
gK > gNa - VG Na channels are inactivated + VG K channels open
At resting potential after an AP:
gK < gNa
gK = gNa
gK > gNa
gK > gNa - VG Na+ channels are inactivated/closed and VG K channels closed – only leak channels open
What two types of refractory periods are there?
Absolute refractory period
Relative refractory period
What is the Absolute refractory period?
The period of time after an AP occurs where it is
impossible to trigger a new AP.
–Mostly due to the post-AP inactivation of most of the VG Na+
channels in the cell
What is the Relative refractory period?
The period of time after an AP occurs where it is
necessary to provide a stronger input in order to trigger an
AP.
– Due mostly to the fact that VG K+ channels are still open,
increasing K+ conductance. The residual inactivation of a few VG Na+ channels also contributes
What comes first after an AP is fired? ARP or RRP?
ARP
The initial rise and final amplitude of an AP
are ?? dependent while the falling phase and
undershoot depend on ??
initial rise = Na+ dep
falling/undershoot = K+ dep
The THRESHOLD for the AP firing is the membrane
potential:
– at which the Na+ influx…
– overcomes the K + efflux…
– resulting in an action potential (or more than one)
When a positive ion or negative ion enters a cell, it is (depolarized/hyperpolarized) which (increases/decreases) the volt.
hyperpolarized - increases
A positive/outward current results in a (increase/decrease) in voltage.
decrease
What current is blocked when TEA is used to isolate the membrane current?
K+ current
What current is blocked when TTX is used to isolate the membrane current?
Na+ current
The early current is mediated by ___________ and the late current is mediated by ________ channels
VG Na+ channels; VG K+ channels
What does membrane conductance (Gion) mean?
the ability of charged ions to move across a cell membrane through protein pores. IT is a measure of the electrical flow from one pt to another
The activation of Na+ and K+ voltage gated
channels is dep on:
voltage
time
both
neither
voltage and time dependent
Na+ and K+ voltage gated
channels open faster at more (depolarized/hyperpolarized) potentials.
depolarized
What has faster kinetics of activation? VG Na+ channels or VG K+ channels
VG Na+
The depolarization of AP including the increase of Na+ current and opening of Na+ channels is a (slow/fast) (negative/positive) cycle.
fast positive
The hyperpolarization of AP including the increase in K+ current and opening of K+ channels is a (slow/fast) (negative/positive) cycle.
slow negative
