Lec 7 Flashcards
What is can be determined by “measuring the amplitude of an ionic current at a series of different voltages imposed on the cell using a voltage clamp “ ?
Voltage dependence
A Current - Voltage relationship shows the total amount of current flowing through all of the channel of a given type at each voltage
T or F?
True
What is defined as “voltages at which the current begins to appear” ?
Voltage Thresholds
Define “inward/outward current” .
the direction that each ion flows at physiological voltages.
IE. Na has inflow current
IE. K+ has outflow current
What is defined as “the voltage at which the Na+ current reverses direction” ?
reversing potential of Na+
When does the “flow” or current of an ion reverse?
When the membrane potential (Vm) is more positive than its threshold.
Whether an individual cahnnel is open or not can be predicted precisely using probabilities
T or F?
False:
CANNOT be predicted with certainty
What 2 events can increase the probability of a ion channel opening?
- Cell membrane voltage
- Concentration of a ligand
Total Conductance (G) will increase with the _______ (increases/decrease) of Voltage.
increase
G is proportionate to voltage
As Po or the total number of open channels increases , the conductance will _______ (increase/decrease).
increase
Po is proportionate to g
What determines the amplitude of total cell current at each current?
1.
2.
- Number of cells that are open
- The current passing through each of them.
The more ______ (positive/negative) the charge, the more channels open.
This is based on which scientific theory?
positive
Ohm’s Law
The number of open channels (Po) depends on voltage
T or F?
True
Current-Voltage relationships (similair to voltage clamp experiments) can be obtained by multiplying :
Total # of channels
x
single channel current
x
___________
(fill in the blank)
Probability of channel opening. (Po)
The probability of a ion channel being open depends on the membrane potential (Vm) _______ (increasing/decreasing) as the membrane is depolarized.
increasing.
If Vm is decreasing then there is a _____ (inflow/outflow) of current. Which ion is most likely responsible?
inflow , Na+
If the Vm is increasing then there must be a ______ (inflow/outflow) of current. The ion that is most likely responsible is?
outflow , K+
Na+ channels have a separate _________ that K+ channels do not.
inactivation gate
Both activation and inactivation are voltage dependent processes that occur when the membrane depolarizes
T or F?
True
Na+ channel “activation gates” are ______
- slower
- faster
than its “inactivation gates” .
Faster
Na+ inactivation gates can open and allow Na+ influx before the process of deactivation closes the channel.
T or F?
False:
Na+ activation channels can open and alllow Na+influx before the process of inacivation closes the channel.
Probability-Voltage graphs are shown at steady state.
T or F?
True
Define “steady state “
means it was measured at infinite time.
What is defined as “opening of an inactivation gate”
recovery from inactivatoin
What is defined as “closing fo an activation gate”
?
Deactivation
Following an “action potential” (or hyperpolarization) the activation gates of both K+ and Na+ will _____ (open/close) and inactivation gates of Na+ channels will ______ (open/close).
activation gates close
inactivation gates open
_________ (activation/inactivation) gates are responsible for the absolute refractory period.
inactivation
During an action potential, Na+ channels undergo _______ (positive/negative) feedback, which in turn activates more Na+ channels and depolarizes the membrane more.
positive
During an action potential K+ channels undergo ______ (positive/negative) feedback and repolarize the cell with the help of Na+’s inactivation gate!
negative
opening of Na+ channels causes an _____ (slow or fast) depolarization toward ENa.
Fast
Opening of K+ channels leads to ____ (slow/fast) repolarization towards EK.
slower
Opening of Na+ channels shifts the permeability of the membrane in favor of PNa
T or F?
True
The inactivation of Na+ channels helps shift the permeability back in favor of PK
T or F?
True
along with the activation of K+ channels
The opening of K+ channels shifts permeability in favor of PNa.
T or F?
False
in favor of PK
Na+ currents turn off while the membrane potential is still high because of ___________, where as K+ currents turn off because , as the membrane potential repolarizes the K+ channels deactivate.
inactivation
