Deck 6: Ionic Basis of the Resting Potential

Question 1

Which is a requirement for a neuron to remain in a stable condition?

A) It must have equal concentrations of intracellular sodium and potassium.
B) It must be osmotically balanced.
C) It must have a small sodium permeability to counteract the sodium-potassium exchange pump.
D) It must have a small chloride permeability to counteract the potassium permeability.
E) The intracellular solution must be electrically negative compared to the extracellular solution.

Answer 1

B

Question 2

Which is true of the potassium equilibrium potential?

A) In neurons, it is usually around 70mV.
B) It describes the membrane potential at which all ionic movement stops.
C) It predicts the membrane potential when the neuron is at steady state.
D) It is the membrane potential where electrical forces and concentration gradients are equal and opposite.
E) It plays little or no role in setting the resting membrane potential.

Answer 2

D

Question 3

Which must be true for an ion to be at equilibrium?

A) The concentrations on both sides of the membrane must be equal.
B) The electrical gradient must match the concentration gradient in the opposite direction.
C) The neuron's membrane potential must be negative.
D) The neuron's membrane potential must be positive.
E) The permeability of the ion must be zero.

Answer 3

B

Question 4

In a model cell, positive ions collect on the outer surface of the cell membrane, while anions collect along the inner surface. These ions are effectively removed from the intracellular and extracellular solutions, leaving these solutions

A) electrically charged.
B) osmotically balanced.
C) ion-deficient.
D) electrically neutral.
E) osmotically imbalanced.

Question 5

Increasing the extracellular potassium concentration causes chloride ions to

A) flow into the cell.
B) flow out of the cell.
C) accumulate in the extracellular space.
D) redistribute to establish equal concentrations on both sides of the cell membrane.
E) do nothing; extracellular potassium concentration does not impact chloride ions.

Question 6

The resting membrane potential for a neuron will depolarize (become less negative) with increased extracellular concentration of which of the following ions?

A) Potassium
B) Sodium
C) Chloride
D) Calcium
E) Anions

Question 7

In a model cell at rest, what is the relative concentration of potassium inside the cell?

A) Lower than the concentration of potassium outside the cell
B) The same as the concentration of potassium outside the cell
C) Higher than the concentration of potassium outside the cell
D) Lower than the sodium concentration inside the cell
E) Lower than the concentration of anions inside the cell

Question 8

The intracellular concentration of sodium in a neuron is

A) much lower than the extracellular concentration.
B) somewhat lower than the extracellular concentration.
C) the same as the extracellular concentration.
D) somewhat higher than the extracellular concentration.
E) much higher than the extracellular concentration.

Question 9

At rest, potassium ions exhibit very low current because the tendency for potassium to flow across the cell membrane because of a concentration gradient is opposed by

A) chloride ions moving across the cell membrane because of a concentration gradient.
B) sodium ions moving across the cell membrane because of a concentration gradient.
C) potassium ions moving across the cell membrane because of the electrical gradient.
D) chloride ions moving across the cell membrane because of the electrical gradient.
E) sodium ions moving across the cell membrane because of the electrical gradient.

Question 10

What happens in a model cell when the extracellular chloride concentration is lowered to half its original value?

A) The membrane potential gets more positive (depolarizes).
B) The membrane potential gets more negative (hyperpolarizes).
C) The membrane potential stays about the same.
D) The equilibrium potential for potassium gets more negative.
E) The equilibrium potential for potassium gets more positive.

Question 11

What happens in a squid giant axon when the extracellular potassium concentration is increased?

A) The membrane potential gets more positive (depolarizes).
B) The membrane potential gets more negative (hyperpolarizes).
C) The membrane potential stays about the same.
D) The equilibrium potential for sodium gets more negative.
E) The equilibrium potential for sodium gets more positive.

Question 12

What happens in a squid giant axon when the extracellular chloride concentration is increased?

A) The membrane potential gets more positive (depolarizes).
B) The membrane potential gets more negative (hyperpolarizes).
C) The membrane potential stays about the same.
D) The equilibrium potential for sodium gets more negative.
E) The equilibrium potential for sodium gets more positive.

Question 13

For a cell at rest, increasing the extracellular sodium ion concentration will cause what movement of sodium ions?

A) Sodium ions will move out of the cell.
B) Sodium ions will move into the cell.
C) Sodium ions will move away from the cell in the extracellular space.
D) Sodium ions will not move because the cell is at equilibrium.
E) Sodium ions will not move because sodium ions cannot cross the cell membrane.

Question 14

For a cell at rest, increasing the extracellular potassium ion concentration will cause what movement of potassium ions?

A) Potassium ions will move out of the cell.
B) Potassium ions will move into the cell.
C) Potassium ions will move away from the cell in the extracellular space.
D) Potassium ions will not move because the cell is at equilibrium.
E) Potassium ions will not move because potassium cannot cross the cell membrane.

Question 15

For a cell at rest, increasing the extracellular chloride ion concentration will cause what movement of chloride ions?

A) Chloride ions will move out of the cell.
B) Chloride ions will move into the cell.
C) Chloride ions will move away from the cell in the extracellular space.
D) Chloride ions will not move because the cell is at equilibrium.
E) Chloride ions will not move because chloride ions cannot cross the cell membrane.

Question 16

What happens when the axoplasm is removed from the giant axon of the squid?

A) Intracellular and extracellular ionic solutions can be controlled and the axon responds normally.
B) Anions removed from the intracellular space are lost and the axon loses function.
C) Ions from the extracellular space move inward, and the axon has a positive resting potential.
D) Ionic concentration can no longer be measured.
E) The membrane produces a weak potential that decays over time.

Question 17

Which of the following is true regarding the sodium permeability for a cell at rest?

A) The sodium permeability is about the same as the potassium permeability.
B) The sodium permeability is about 50% smaller than the potassium permeability.
C) The sodium permeability is about 75% smaller than the potassium permeability.
D) The sodium permeability is about 90% smaller than the potassium permeability.
E) The cell membrane is not permeable to sodium at rest.

Question 18

What is the purpose of the constant field equation?

A) To determine the equilibrium potential of a single ion
B) To determine the membrane potential when potassium and chloride are present.
C) To determine the resting potential of a cell given all ionic concentrations and conductances
D) To determine which ions are moving across the membrane at rest
E) To determine the minimum voltage at which ionic movement can be balanced

Question 19

Which of these conditions is assumed under the constant field equation?

A) Equal conductance for sodium and potassium
B) Zero net ionic current
C) High chloride conductance
D) High potassium conductance
E) Low sodium conductance

Question 20

Ionic conductance is a measure of

A) the electrical charge of an ion.
B) the charge strength of an ion.
C) the resistance of an ion to movement.
D) the equilibrium potential of an ion.
E) how easily the ion can move across the membrane.

Question 21

The driving force on an ion is defined as the difference between the

A) membrane potential and the threshold potential.
B) conductance of an ion and the membrane potential.
C) membrane potential and the equilibrium potential for that ion.
D) fraction of ions on the intracellular and extracellular membranes.
E) sodium and potassium equilibrium potentials.

Question 22

For a membrane potential to remain stable, which of the following must be true?

A) The potassium conductance must be equal to zero.
B) The sum of all ionic currents must be equal to zero.
C) The chloride and potassium equilibrium potentials must be the same.
D) The chloride and sodium currents must be equal.
E) The chloride and potassium conductances must be equal.

Question 23

In a cell at rest, the driving force on sodium is high, while the permeability of sodium is low. As a consequence, which of the following is true of the cell's membrane potential at rest?

A) Sodium ion concentrations have a small influence on the resting membrane potential.
B) Small changes in extracellular sodium concentration will have a large impact on the membrane potential.
C) Sodium is at equilibrium at the resting membrane potential.
D) Small changes in the intracellular sodium concentration will have a large impact on the membrane potential.
E) Sodium ion concentrations do not contribute to the resting membrane potential.

Question 24

The membrane potential of a cell depends on the relative conductances of the membrane to the major ions, and on the

A) permeability of these ions.
B) charge of these ions.
C) concentrations of these ions.
D) size of these ions.
E) equilibrium potentials of these ions.

Question 25

At the neuron's resting membrane potential, chloride ions are at equilibrium; what else must be true?

A) The driving forces on sodium and potassium are equal and in opposite directions.
B) The concentrations of sodium and potassium are equal on opposite sides of the membrane.
C) The permeability of the membrane to sodium and potassium are equal.
D) The ratio of sodium to potassium is equal on opposite sides of the membrane.
E) The products of the driving force and permeability for sodium and potassium are equal and opposite.

Question 26

In the term "steady state," what is steady?

A) The net passive loss of solutes from the cell
B) The composition of the cytoplasm
C) The leaking of solutes into the cell
D) The activity of ion pumps
E) The direction in which sodium and potassium are moving

Question 27

In order to maintain the neuronal membrane potential at steady state, which must occur?

A) ATP must be produced and used by the cell.
B) The potassium conductance must be low.
C) The membrane must be impermeable to sodium.
D) The sodium current must be zero.
E) The chloride equilibrium potential must be less than that for potassium.

Question 28

Which of these is not a factor in determining the membrane potential for a cell?

A) The concentration of sodium ions inside and outside the cell
B) The concentration of potassium ions inside and outside the cell
C) The relative permeability (or conductance) of the membrane to sodium and potassium ions
D) The ratio of the actions of the sodium-potassium exchange
E) The type of cell being studied (e.g., glia, muscle, neuron)

Question 29

The action of the sodium-potassium exchange pump is electrogenic. What does this mean?

A) The exchange pump uses the electrical gradient to pump ions..
B) The exchange pump produces an electrical charge.
C) The exchange pump is responsible for the membrane potential.
D) The exchange pump counteracts the effect of the electrical gradient.
E) The exchange pump uses ions to pump water out of the cell.

Question 30

Why is the sodium-potassium exchange pump necessary?

A) To establish a resting membrane potential
B) To counteract the loss of chloride ions from the cell
C) To ensure osmotic balance
D) To keep sodium and potassium flux at a steady state
E) To maintain equal numbers of positive and negative charges across the membrane

Question 31

Which of the following is true for the sodium-potassium exchange pump?

A) It pumps an equal number of ions into and out of the cell.
B) It passively distributes ions along their concentration gradient.
C) It passively distributes ions along their electrical gradient.
D) It pumps two potassium ions into the cell and three sodium ions out of the cell.
E) It is unrelated to maintaining ion balance in the cell.

Question 32

Values for neuronal resting membrane potentials vary widely, from -90mV to -40mV. This is primarily due to differences in

A) external potassium concentration.
B) external sodium concentration.
C) the sodium-potassium exchange pump.
D) the chloride conductance.
E) the sodium-to-potassium permeability ratio.

Question 33

What is the approximate maximum value that the sodium-potassium exchange pump can contribute to the resting membrane potential?

A) -5 mV
B) -11 mV
C) -24 mV
D) -75 mV
E) -90 mV

Question 34

The flow of potassium ions out of the cell is countered by which of the following?

A) An outward flow of chloride ions
B) An inward flow of chloride ions
C) An outward flow of sodium ions
D) An outward flow of calcium ions
E) The sodium-potassium exchange pump

Question 35

What is the ratio of sodium to potassium exchange for each cycle of the sodium-potassium exchange pump?

A) 1 sodium: 1 potassium
B) 2 sodium: 1 potassium
C) 3 sodium: 2 potassium
D) 2 sodium: 3 potassium
E) 1 sodium: 2 potassium

Question 36

The action of ion channels to allow current to flow through the membrane can be thought of as which of the following electrical components?

A) Capacitor
B) Battery
C) Wires
D) Resistor
E) Voltmeter

Question 37

The equilibrium potential for an ion can be considered as which of the following electrical components?

A) Capacitor
B) Battery
C) Wires
D) Resistor
E) Voltmeter

Question 38

In the squid axon, potassium contributes approximately how much to the resting membrane potential?

A) 15%
B) 30%
C) 45%
D) 60%
E) 75%

Question 39

In a biological neuron at rest, there is a constant flow of potassium ions out of the cell. This flow is called the

A) restive current.
B) sodium-potassium exchange pump current.
C) leak current.
D) electrogenic current.
E) passive current.

Question 40

What is the most abundant source of potassium to flow out of the cell at the resting membrane potential?

A) The sodium-potassium exchange pump
B) 2P channels
C) M channels
D) The omega current
E) HCN channels

Question 41

Which of the following is true regarding HCN channels in the neuronal membrane?

A) They are responsible for the bulk of the flow of potassium from the cell at rest.
B) They are voltage-activated at hyperpolarized membrane potentials.
C) They are nonspecific ion channels that allow chloride ions to flow into the cell.
D) They have a 4:1 ratio of potassium to sodium, allowing sodium to flow into the cell.
E) They are blocked by tetrodotoxin.

Question 42

Whether an increase in chloride permeability is hyperpolarizing or depolarizing depends on

A) the equilibrium potential for sodium.
B) the relationship between the chloride equilibrium potential and the membrane potential.
C) whether there is active transport of chloride across the membrane.
D) the equilibrium potential for potassium.
E) the neuronal membrane potential.

Question 43

Name three conditions that must be met for a cell to remain in a stable condition.

Question 44

Explain what is meant by the equilibrium potential for an ion?

Question 45

Explain why the charge separation across the cell membrane does not violate the principle of electrical neutrality.

Question 46

Why does a neuronal membrane potential change with increases in extracellular potassium concentration, but does not change with an increase in extracellular chloride concentration?

Question 47

At rest, a cell's membrane potential is near, but not equal to, the potassium equilibrium potential. Explain why this is the case.

Question 48

Name two features of the squid giant axon that make it particularly suitable for experiments on membrane potentials.

Question 49

In retinal ganglion cells, the sodium leak current is relatively large. Explain the effect this has on the resting membrane potential for these cells.

Question 50

You are conducting an experiment recording the membrane potential of the squid giant axon. You decide to increase the extracellular concentration of potassium from 10 mM to 30 mM, and then to 200mM. What is the effect on the membrane potential in each case? How do these results compare to the values you would expect from the Nernst equation? Why?

Question 51

In 1902, Bernstein postulated that the membrane potential was due to differences in the concentration of Potassium in the intracellular and extracellular fluids. How did Goldman, Hodgkin and Katz refine this relationship to model the membrane potential more exactly?

Question 52

Explain how the actions of the sodium-potassium exchange pump maintains a cell's internal concentrations of sodium and potassium.

Question 53

Describe the following components of the neuron in terms of their electrical properties: The cell membrane, ion equilibrium potentials, ion channels.

Question 54

In modifying the Constant Field Equation, why is it necessary to account for the ratio of potassium to sodium permeability?

Question 55

Explain how the sodium-potassium exchange pump contributes to the membrane potential, and how you can predict the magnitude of its effect.

Question 56

In your neurology practice, you meet a patient who complains of a temporary inability to move her legs, a condition that lasts for hours to days at a time. What is your diagnosis, including a description of the molecular mechanism that underlies this condition?

Question 57

How would an increase in chloride conductance affect the changes in the membrane potential?