11.23 A

Question 1

Define a current as it relates to action potentials.

Answer 1

the movement of ions across the cell membrane

Question 2

What is V as it relates to action potentials?

Answer 2

the membrane potential

Question 3

The membrane potential is a measure of the potential of _____ relative to _____.

Answer 3

the cytoplasm relative to the bath

Question 4

What are the two forces that drive ion movement?

Answer 4

• electrical due to the membrane potential

- chemical due to an ion concentration gradient

Question 5

When membrane potential is negative, there is a force pulling what sorts of ions into the cell?

Answer 5

cations

Question 6

When membrane potential is positive, there is a force pushing what sorts of ions out of the cell?

Answer 6

cations

Question 7

The Nernst potential of an ion is a measure of what force driving it’s movement?

Answer 7

the chemical force

Question 8

What is the equation for Nernst potential?

Answer 8

E = (60/z)log(extracellular/intracellular concentration)

Question 9

There will be no net movement of a particular ion across a membrane when what is true?

Answer 9

the electrical and chemical forces driving it’s movement are balanced out

Question 10

Under normal conditions, in which direction does potassium move relative to the cytoplasm?

Answer 10

potassium moves out of the cell

Question 11

Are currents defined in terms of movement of positive or negative ions?

Answer 11

positive ions

Question 12

Positive currents have what affect on V?

Answer 12

they make it more negative because cations are leaving the cytoplasm

Question 13

Sodium ions will generate a (positive/negative) current?

Answer 13

negative

Question 14

Describe the flow of ions across a membrane that will generate a negative current?

Answer 14

cations moving into the cell

Question 15

A repolarizing current is a (positive/negative) one.

Answer 15

positive

Question 16

Define flux.

Answer 16

the direction of movement of an ion

Question 17

How is current different from flux?

Answer 17

flux is the direction of movement of an ion where as current is strictly the direction of movement of a cation

Question 18

The magnitude of an ion’s current will depend on what two things?

Answer 18

the forces driving the movement (chemical and electrical) and the conductance

Question 19

What is conductance?

Answer 19

how easily the ion can move across the membrane, it is the inverse of resistance

Question 20

Membrane potential describes the ___ force driving ion movement whereas Nernst potential describes the ____ force driving ion movement.

Answer 20

membrane = electrical, Nernst = chemical

Question 21

Conductance is dependent on what three things?

Answer 21

• number of open ion channels
• the presence of leak channels
• ion concentration

Question 22

How does conductance of potassium change if the extracellular potassium concentration is increased and all other factors remain unchanged?

Answer 22

the potassium conductance will also increase, and ions will be able to leave the cell more easily

Question 23

The conductance of potassium is proportional to what other factor?

Answer 23

the extracellular concentration of potassium

Question 24

Give an equation for the current of an ion moving across a cell membrane.

Answer 24

I = g (V - E) = conductance (membrane potential - Nernst potential)

Question 25

The sign of what defines the sign of an ion’s current?

Answer 25

the sign of (V - E)

Question 26

What is the typical resting membrane potential in a cell?

Answer 26

-70 mV to -80 mV, very close to the Nernst potential of potassium

Question 27

If the conductance of a particular ion is increased, what will happen to the membrane potential?

Answer 27

it will move closer to that ion’s Nernst potential

Question 28

The current across a cell membrane is zero when what is true?

Answer 28

there is no net movement of ions across that membrane

Question 29

Describe the structure of the voltage-gated sodium channel?

Answer 29

it is a channel with two gates, an activation gate and an inactivation gate; if either gate is closed, sodium cannot pass through the channel

Question 30

Describe a resting voltage-gated sodium channel under normal conditions.

Answer 30

the activation gate is closed and teh inactivation gate is open

Question 31

At resting potential, how can the magnitude of the sodium current be equal to the potassium current?

Answer 31

although the conductance of potassium is significantly greater, the (V - E) of sodium is larger than that of potassium

Question 32

If at resting membrane potential, the membrane potential is stable, what must be true about the currents of potassium and sodium?

Answer 32

they must be equal but opposite

Question 33

If a cell is only permeable to sodium and potassium, what is true about their combined fractional conductances?

Answer 33

they equal 1

Question 34

Give an equation relating the value of the membrane potential to the fractional conductance and Nernst potential of potassium and sodium.

Answer 34

V = (fg1 x E1) + (fg2 x E2)