Exam 1 - Lecture 9/4 Flashcards
Cell Polarization
A difference in electrical charge between inside and outside the cell. Inside usually negative at rest, Outside usually positive.
Cells are _____ at rest.
Polarized. (-mV @ Vrm).
Depolarized
To become less polar (more charged). Usually this is being stimulated or turned on.
Hyperpolarized
To become more polar (more negative charged). Usually means inhibiting or more difficult to excite.
e.g. Going from -80 to +30, back down to -90 before returning to rest at -80. Very short period of time more negative than -80, usually shortly after repolarizing or when something negative enters cell at rest.
Repolarization
To return to Vrm from a depolarized state. i.e. Renormalize the the charge back to resting polarity.
Action potential
-80mV at resting, Depolarization occurs to bring mV to +35 (overshoot above 0), Depolarization to return mV to resting state at -80mV. May or may not hyperpolarize during depolarization to -90mV before returning to -80mV.
What channels may be open during Hyperpolarization?
Extra K+ channels (-90mV).
What channels are open during Depolarization?
Ions with positive mV e.g. Sodium channels (+60mV.)
Overshoot
Resting membrane potential going above 0 to a positive state.
Voltage-gated Na+ channels
- Very fast Na+ channels, selective for only Na+.
Outside gate for Fast Na+ channels
Activation gate, also called M-gate.
Inside gate for Fast Na+ channels
Inactivation gate, also called H-gate.
At rest, what are the gates for the Fast Na+ channel?
M-gate is closed and H-gate is open
When cell depolarizes to threshold potential, activation (m-gate) gates ______.
Opens.
What drugs affect these Na+ channels?
Any drug ending in -caine.
e.g. Lidocaine
After M-gate opens, what happens quickly?
H-gate closes very shortly after M-gate opens.
Once H-gate is shut, what happens during repolarization?
M-gate will close, then H-gate can open again at resting mV, finalizing repolarization.
Voltage-gated K+ channels characteristics
- Only one gate on the inside of the channel.
- Very slow compared to “Fast” Na+ V-G channels.
- Open during cell Repolarization, close at the end.
Cell may become hyper polarized because of how slow this gate is.
Voltage-gated K+ channels.
Fast Na+ channels are open during:
Depolarization
Fast Na+ channels are closed during:
Repolarization
V-G K+ are open during:
Repolarization
V-G K+ channels are closed during:
Depolarization
Conductance
Ease of ion to get across the cell wall, aka ion flow
Permeability of Na+ increases rapidly during
Depolarization
Describe the action potential time course
Following threshold stimulus, fast Na+ channels open, pNa+ increases rapidly, Na+ channels are inactivated, V-G K+ channels open, cell returns to Vrm.
If Na+ channels don’t close rapidly, what can happen to the heart?
Arrhythmias such as V-fib.
IF membrane was equally permeable to K+ and Na+, what would the resting mV of the cell be?
-15mv
What is the total range of mV for a cell that is permeable to only K+ and Na+?
150mv (-90mV to +60mV)
If pt is hyperkalemic, what happens to the resting mV of a cell?
It becomes less negative, let’s say -70mV, due to the Nernst potential equation becoming 120/8 rather than 120/4. This affects heart function and can cause arrhythmias.
The more negative the cell, the harder to ___.
Excite/turn on
What would make a cell even more negative?
Low K+, due to Nernst equation being 120/2, making it a 60:1 ratio.
If the cell resting mV is only -60, off of the baseline of -80, what could happen to the Fast Na+ channels?
Might not restart, due to cell not achieving baseline mV. Leads to slower HR and transduction.
What decides the driving force of an ion?
The charge of the ion, concentration gradient, and charge inside cell.
e.g. Resting cell mV is -80. Calcium has a 1:10,000 inside-out gradient, has 2 positive charges, and inside the cell is negative… therefore Ca++ has the largest driving force.
If inside of the cell is +35mV, what happens to driving force of Na+ and Ca++?
Reduced, because inside of the cell is already positive and those are positive ions that are greater outside the cell.
If cell has a +1000 mV, what would happen to Na+?
Would be pushed outside the cell because it has a +mV, even going against its concentration gradient.
At what cell mV should Na+ be prevented from entering the cell?
+60mv, because that’s equal to sodiums mV.
Equilibrium potential
mV of inside the cell that prevents that ion from coming in
e.g. cell mV is +60, therefore Na+ will not enter cell.
e.g. K+ wants to leave cell until the mV is -90.
At rest, does sodium leak in/out of cell?
At rest, sodium will leak INTO the cell due to its concentration gradient AND the -mV of the cell.
At rest, does potassium leak in/out of cell?
No. Even though the concentration gradient would have potassium leaking out of the cell, the -80mV keeps potassium (a positive ion) from leaving.
mV is not always moving (a “current”), just the ______ for a current.
Potential.
If cell mV was -50, and a mystery ion had a negative charge, what would its concentration gradient be?
Higher outside the cell, wanting to flow inward. The negative mV inside the cell would prevent the negative ion from leaking in.
If a cell’s baseline is -50mV, and it suddenly became more negative to -80mV, what would happen to the negative ions inside the cell?
They would get pushed out, against their concentration gradient.
