Exam 1 - Lecture 9/4

Question 1

Cell Polarization

Answer 1

A difference in electrical charge between inside and outside the cell. Inside usually negative at rest, Outside usually positive.

Question 2

Cells are _____ at rest.

Answer 2

Polarized. (-mV @ V_rm).

Question 3

Depolarized

Answer 3

To become less polar (more charged). Usually this is being stimulated or turned on.

Question 4

Hyperpolarized

Answer 4

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.

Question 5

Repolarization

Answer 5

To return to V_rm from a depolarized state. i.e. Renormalize the the charge back to resting polarity.

Question 6

Action potential

Answer 6

-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.

Question 7

What channels may be open during Hyperpolarization?

Answer 7

Extra K+ channels (-90mV).

Question 8

What channels are open during Depolarization?

Answer 8

Ions with positive mV e.g. Sodium channels (+60mV.)

Question 9

Overshoot

Answer 9

Resting membrane potential going above 0 to a positive state.

Question 10

Voltage-gated Na+ channels

Answer 10

• Very fast Na+ channels, selective for only Na+.

Question 11

Outside gate for Fast Na+ channels

Answer 11

Activation gate, also called M-gate.

Question 12

Inside gate for Fast Na+ channels

Answer 12

Inactivation gate, also called H-gate.

Question 13

At rest, what are the gates for the Fast Na+ channel?

Answer 13

M-gate is closed and H-gate is open

Question 14

When cell depolarizes to threshold potential, activation (m-gate) gates ______.

Answer 14

Opens.

Question 15

What drugs affect these Na+ channels?

Answer 15

Any drug ending in -caine.

e.g. Lidocaine

Question 16

After M-gate opens, what happens quickly?

Answer 16

H-gate closes very shortly after M-gate opens.

Question 17

Once H-gate is shut, what happens during repolarization?

Answer 17

M-gate will close, then H-gate can open again at resting mV, finalizing repolarization.

Question 18

Voltage-gated K+ channels characteristics

Answer 18

• 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.

Question 19

Cell may become hyper polarized because of how slow this gate is.

Answer 19

Voltage-gated K+ channels.

Question 20

Fast Na+ channels are open during:

Answer 20

Depolarization

Question 21

Fast Na+ channels are closed during:

Answer 21

Repolarization

Question 22

V-G K+ are open during:

Answer 22

Repolarization

Question 23

V-G K+ channels are closed during:

Answer 23

Depolarization

Question 24

Conductance

Answer 24

Ease of ion to get across the cell wall, aka ion flow

Question 25

Permeability of Na+ increases rapidly during

Answer 25

Depolarization

Question 26

Describe the action potential time course

Answer 26

Following threshold stimulus, fast Na+ channels open, pNa+ increases rapidly, Na+ channels are inactivated, V-G K+ channels open, cell returns to V_rm.

Question 27

If Na+ channels don’t close rapidly, what can happen to the heart?

Answer 27

Arrhythmias such as V-fib.

Question 28

IF membrane was equally permeable to K+ and Na+, what would the resting mV of the cell be?

Answer 28

-15mv

Question 29

What is the total range of mV for a cell that is permeable to only K+ and Na+?

Answer 29

150mv (-90mV to +60mV)

Question 30

If pt is hyperkalemic, what happens to the resting mV of a cell?

Answer 30

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.

Question 31

The more negative the cell, the harder to ___.

Answer 31

Excite/turn on

Question 32

What would make a cell even more negative?

Answer 32

Low K+, due to Nernst equation being 120/2, making it a 60:1 ratio.

Question 33

If the cell resting mV is only -60, off of the baseline of -80, what could happen to the Fast Na+ channels?

Answer 33

Might not restart, due to cell not achieving baseline mV. Leads to slower HR and transduction.

Question 34

What decides the driving force of an ion?

Answer 34

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.

Question 35

If inside of the cell is +35mV, what happens to driving force of Na+ and Ca++?

Answer 35

Reduced, because inside of the cell is already positive and those are positive ions that are greater outside the cell.

Question 36

If cell has a +1000 mV, what would happen to Na+?

Answer 36

Would be pushed outside the cell because it has a +mV, even going against its concentration gradient.

Question 37

At what cell mV should Na+ be prevented from entering the cell?

Answer 37

+60mv, because that’s equal to sodiums mV.

Question 38

Equilibrium potential

Answer 38

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.

Question 39

At rest, does sodium leak in/out of cell?

Answer 39

At rest, sodium will leak INTO the cell due to its concentration gradient AND the -mV of the cell.

Question 40

At rest, does potassium leak in/out of cell?

Answer 40

No. Even though the concentration gradient would have potassium leaking out of the cell, the -80mV keeps potassium (a positive ion) from leaving.

Question 41

mV is not always moving (a “current”), just the ______ for a current.

Answer 41

Potential.

Question 42

If cell mV was -50, and a mystery ion had a negative charge, what would its concentration gradient be?

Answer 42

Higher outside the cell, wanting to flow inward. The negative mV inside the cell would prevent the negative ion from leaking in.

Question 43

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?

Answer 43

They would get pushed out, against their concentration gradient.