Ionic Basis Of The Action Potential Chapter 7 Test Bank Docx

Chapter 7: Ionic Basis of the Action Potential

Test Bank

Type: multiple choice question

Title: Chapter 07 - Question 01

1. In a voltage clamp, which of the following is measured?

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Name two features of the membrane current that the voltage clamp method can measure.

Bloom’s Level: 2. Understanding

a. Magnitude of the ionic current

b. Direction of the ionic current

c. What ion is responsible for the current

d. a and b only

e. a, b and c

Type: multiple choice question

Title: Chapter 07 - Question 02

2. How does a voltage clamp work?

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Describe, in general terms, the experimental arrangement for voltage clamp experiments.

Bloom’s Level: 2. Understanding

a. It measures the voltage of a neuron that is placed in the preparation.

b. It changes the membrane potential of a neuron using two extracellular electrodes.

c. It holds the current across a neuronal membrane constant and measures the changes in voltage.

d, It holds the voltage of a neuron constant by injecting current equal to the ionic current passing across the cell membrane.

e. It inactivates ion channels so that the only current passing into the cell is delivered by the equipment.

Type: multiple choice question

Title: Chapter 07 - Question 03

3. In a voltage clamp experiment, this current is observed immediately after a voltage step and varies linearly with the size of the voltage step.

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Distinguish between capacitative currents and leak currents.

Bloom’s Level: 2. Understanding

a. Capacitative current

b. Leak current

c. Sodium current

d. Potassium current

e. Calcium current

Type: multiple choice question

Title: Chapter 07 - Question 04

4. In a voltage clamp experiment, this current is observed immediately after a voltage step and lasts approximately 20 microseconds or less.

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Distinguish between capacitative currents and leak currents.

Bloom’s Level: 2. Understanding

a. Capacitative current

b. Leak current

c. Sodium current

d. Potassium current

e. Calcium current

Type: multiple choice question

Title: Chapter 07 - Question 05

5. Following the application of a depolarizing stimulus, which of the following occurs first in a neuron?

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Explain how the movement of sodium and potassium is involved in producing action potentials in nerve cell membranes.

Bloom’s Level: 2. Understanding

a. Afterdepolarizing potential

b. Afterhyperpolarizing potential

c. Activation of sodium channels

d. Activation of potassium channels

e. Inactivation of sodium channels

Type: multiple choice question

Title: Chapter 07 - Question 06

6. An increase in the sodium conductance results in which of the following?

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Explain how the movement of sodium and potassium is involved in producing action potentials in nerve cell membranes.

Bloom’s Level: 3. Applying

a. A depolarization of the neuronal membrane potential

b. A hyperpolarization of the neuronal membrane potential

c. A repolarization of the neuronal membrane potential

d. An action potential

e. An afterhyperpolarizing potential

Type: multiple choice question

Title: Chapter 07 - Question 07

7. The late current observed in voltage clamp experiments contributes to which of these phases of the action potential?

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Explain how the movement of sodium and potassium is involved in producing action potentials in nerve cell membranes.

Bloom’s Level: 5. Evaluating

a. Depolarization

b. Inactivation

c. Repolarization

d. Threshold

e. Refractory period

Type: multiple choice question

Title: Chapter 07 - Question 08

8. The early current observed in voltage clamp experiments contributes to which of these phases of the action potential?

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Explain how the movement of sodium and potassium is involved in producing action potentials in nerve cell membranes.

Bloom’s Level: 5. Evaluating

a. Depolarization

b. Inactivation

c. Repolarization

d. Threshold

e. Refractory period

Type: multiple choice question

Title: Chapter 07 - Question 09

9. Which of the following ions is responsible for the late current following a voltage step in a voltage clamp experiment?

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Explain how the movement of sodium and potassium is involved in producing action potentials in nerve cell membranes.

Bloom’s Level: 4. Analyzing

a. Sodium

b. Potassium

c. Chloride

d. Calcium

e. Magnesium

Type: multiple choice question

Title: Chapter 07 - Question 10

10. In a voltage clamp experiment, you record from a neuron after a command voltage step to -10 mV. In a second experiment, you step the command voltage to +50 mV. What do you notice about the sodium current in the second experiment, compared to the first?

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Explain how membrane potential affects the magnitude and time course of ion currents.

Bloom’s Level: 4. Analyzing

a. The sodium current is larger.

b. The sodium current is smaller.

c. The sodium current is the same magnitude.

d. The sodium current appears earlier in time.

e. The sodium current appears later in time.

Type: multiple choice question

Title: Chapter 07 - Question 11

11. In a voltage clamp experiment, you observe that the magnitude of the sodium current increases when the membrane potential is stepped between -45 and +10 mV. Why?

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Explain how membrane potential affects the magnitude and time course of ion currents.

Bloom’s Level: 4. Analyzing

a. The driving force on sodium increases as membrane potential increases.

b. The equilibrium potential for sodium increases as membrane potential increases.

c. More sodium channels open as membrane potential increases.

d. The resting potential of the neuron increases as membrane potential increases.

e. The leak conductance increases as membrane potential increases.

Type: multiple choice question

Title: Chapter 07 - Question 12

12. In a voltage clamp experiment, you observe that the magnitude of the sodium current decreases when the membrane potential is stepped between +10 and +50 mV. Why?

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Explain how membrane potential affects the magnitude and time course of ion currents.

Bloom’s Level: 4. Analyzing

a. The driving force on sodium decreases as membrane potential increases.

b. The equilibrium potential for sodium decreases as membrane potential increases.

c. The voltage difference opens fewer sodium channels as membrane potential increases.

d. The resting potential of the neuron decreases as membrane potential increases.

e. The leak conductance decreases as membrane potential increases.

Type: multiple choice question

Title: Chapter 07 - Question 13

13. Which of the following can be attributed to the flow of sodium ions across the membrane?

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Name the three distinct processes that follow depolarization of the nerve membrane.

Bloom’s Level: 2. Understanding

a. Capacitative current

b. Gating current

c. Early current

d. Late current

e. Afterhyperpolarizing potential (AHP)

Type: multiple choice question

Title: Chapter 07 - Question 14

14. Which of the following depends on the flow of potassium ions across the membrane?

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Name the three distinct processes that follow depolarization of the nerve membrane.

Bloom’s Level: 2. Understanding

a. Capacitative current

b. Gating current

c. Early current

d. Late current

e. Afterdepolarizing potential (ADP)

Type: multiple choice question

Title: Chapter 07 - Question 15

15. What ion is responsible for the outward current seen in a voltage clamp experiment where the voltage is set to +25 mV?

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Name the three distinct processes that follow depolarization of the nerve membrane.

Bloom’s Level: 3. Applying

a. Sodium

b. Potassium

c. Calcium

d. Magnesium

e. Chloride

Type: multiple choice question

Title: Chapter 07 - Question 16

16. You are performing a voltage clamp experiment in which the neuron’s resting potential is -70 mV. When you change the command voltage to + 40 mV, what is the first current that you observe?

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Name the three distinct processes that follow depolarization of the nerve membrane.

Bloom’s Level: 3. Applying

a. Capacitative current

b. Inward potassium current

c. Inward sodium current

d. Outward potassium current

e. Outward sodium current

Type: multiple choice question

Title: Chapter 07 - Question 17

17. A neuron bathed in a fluid containing Saxitoxin (STX) is held a in a voltage clamp experiment and the command voltage is stepped to -15 mV. Which of the following currents is observed?

Feedback: Subhead: Voltage Clamp Experiments

Learning Objective: Name the three distinct processes that follow depolarization of the nerve membrane.

Bloom’s Level: 3. Applying

a. Outward sodium current

b. Inward sodium current

c. Outward potassium current

d. Inward potassium current

e. No currents are observed

Type: multiple choice question

Title: Chapter 07 - Question 18

18. The use of choline instead of sodium in the extracellular solution allowed Hodgkin and Huxley to eliminate which of the following from their experiments?

Feedback: Subhead: Quantitative Description of Sodium and Potassium Conductances

Learning Objective: Discuss the value of Hodgkin and Huxley’s work that mathematically described sodium and potassium conductances.

Bloom’s Level: 2. Understanding

a. Driving force on sodium

b. Driving force on potassium

c. Membrane potential fluctuation

d. Leak currents

e. Capacitative currents

Type: multiple choice question

Title: Chapter 07 - Question 19

19. Hodgkin and Huxley found a delayed potassium conductance that occurred following membrane depolarization but not hyperpolarization. For this reason, this conductance was called the

Feedback: Subhead: Quantitative Description of Sodium and Potassium Conductances

Learning Objective: Discuss the value of Hodgkin and Huxley’s work that mathematically described sodium and potassium conductances.

Bloom’s Level: 2. Understanding

a. depolarizing conductance.

b. rightward shift.

c. s-curve.

d. onward conductance.

e. delayed rectifier.

Type: multiple choice question

Title: Chapter 07 - Question 20

20. Hodgkin and Huxley found that the delayed potassium conductance could be described mathematically by the product of four exponential equations. This suggests that

Feedback: Subhead: Quantitative Description of Sodium and Potassium Conductances

Learning Objective: Discuss the value of Hodgkin and Huxley’s work that mathematically described sodium and potassium conductances.

Bloom’s Level: 4. Analyzing

a. there are four potassium channels present in the neuron.

b. the opening of potassium channels depends on four independent events.

c. the potassium channel is made up of a single monomeric protein.

d. the potassium current will increase exponentially with membrane potential.

e. the opening of potassium channels is delayed.

Type: multiple choice question

Title: Chapter 07 - Question 21

21. By subtracting the potassium current from the total ion current in their experiments, Hodgkin and Huxley were able to determine the

Feedback: Subhead: Quantitative Description of Sodium and Potassium Conductances

Learning Objective: Discuss the value of Hodgkin and Huxley’s work that mathematically described sodium and potassium conductances.

Bloom’s Level: 4. Analyzing

a. magnitude of the calcium current.

b. duration of the calcium current.

c. magnitude of the sodium current.

d. magnitude and duration of the sodium current.

e. contribution of potassium to the resting membrane potential.

Type: multiple choice question

Title: Chapter 07 - Question 22

22. By calculating the ionic conductances in the neuronal membrane, Hodgkin and Huxley were able to

Feedback: Subhead: Quantitative Description of Sodium and Potassium Conductances

Learning Objective: Discuss the value of Hodgkin and Huxley’s work that mathematically described sodium and potassium conductances.

Bloom’s Level: 3. Applying

a. describe the time course of the action potential.

b. predict the molecular makeup of the voltage-gated ion channels.

c. explain the basis of the refractory period.

d. explain the threshold membrane potential.

e. do all of the above.

Type: multiple choice question

Title: Chapter 07 - Question 23

23. When Hodgkin and Huxley recorded from a neuron under voltage clamp at +52 mV, which of the following describes what they observed?

Feedback: Subhead: Quantitative Description of Sodium and Potassium Conductances

Learning Objective: Discuss the value of Hodgkin and Huxley’s work that mathematically described sodium and potassium conductances.

Bloom’s Level: 4. Analyzing

a. An inward early current followed by an outward late current

b. No early current and an outward late current

c. An outward early current followed by an inward late current

d. An outward early current followed by an outward late current

e. An inward early current followed by no late current

Type: multiple choice question

Title: Chapter 07 - Question 24

24. Which of the following is true of sodium and potassium conductances in neurons?

Feedback: Subhead: Quantitative Description of Sodium and Potassium Conductances

Learning Objective: Discuss the value of Hodgkin and Huxley’s work that mathematically described sodium and potassium conductances.

Bloom’s Level: 4. Analyzing

a. They both increase with an increase in the membrane potential.

b. They both decrease with an increase in the membrane potential.

c. Sodium conductance increases, while potassium conductance decreases, with an increase in the membrane potential.

d. Sodium conductance decreases, while potassium conductance increases, with an increase in the membrane potential.

e. None of these describe the relationship between ion conductance and membrane potential.

Type: multiple choice question

Title: Chapter 07 - Question 25

25. When triethanolamine (TEA) is applied to a neuron in a voltage clamp experiment, what results are observed?

Feedback: Subhead: Quantitative Description of Sodium and Potassium Conductances

Learning Objective: Discuss the value of Hodgkin and Huxley’s work that mathematically described sodium and potassium conductances.

Bloom’s Level: 4. Analyzing

a. An inward early current followed by an outward late current

b. No early current and an outward late current

c. An outward early current followed by an inward late current

d. An outward early current followed by an outward late current

e. An inward early current followed by no late current

Type: multiple choice question

Title: Chapter 07 - Question 26

26. During the late phase of an action potential, the threshold for activating a subsequent action potential is larger than when the neuron is at rest. This relative refractory period is due to a very large

Feedback: Subhead: Quantitative Description of Sodium and Potassium Conductances

Learning Objective: Discuss the value of Hodgkin and Huxley’s work that mathematically described sodium and potassium conductances.

Bloom’s Level: 3. Applying

a. increase in sodium conductance.

b. increase in potassium conductance.

c. decrease in potassium conductance.

d. increase in chloride conductance.

e. decrease in calcium conductance.

Type: multiple choice question

Title: Chapter 07 - Question 27

27. What is the source of the gating currents?

Feedback: Subhead: Gating Currents

Learning Objective: Explain what gating currents are.

Bloom’s Level: 2. Understanding

a. Movement of ions across the cell membrane

b. Ion movement associated with the capacitance (“charging”) of the cell membrane

c. Changes in the conductance of ion channels

d. Translocation of charged residues in ion channel proteins

e. Influx of calcium from the extracellular space

Type: multiple choice question

Title: Chapter 07 - Question 28

28. What is thought to be the functional significance of charged amino acids along the S4 helix of the voltage-gated sodium channel?

Feedback: Subhead: Mechanisms of Activation and Inactivation

Learning Objective: Describe two different channel structures associated with activating and inactivating ion channels.

Bloom’s Level: 2. Understanding

a. They form the basis for sodium selectivity of the channel.

b. They provide a mechanism for inactivation.

c. They attract the negative charges of nearby channel subunits, forming a functional protein.

d. They form the pore of the channel.

e. They provide the gating mechanism for channel opening.

Type: multiple choice question

Title: Chapter 07 - Question 29

29. In the rotational model of sodium channel activation, what happens when the membrane is depolarized?

Feedback: Subhead: Mechanisms of Activation and Inactivation

Learning Objective: Describe two different channel structures associated with activating and inactivating ion channels.

Bloom’s Level: 3 Applying

a. An activation “gate” on the N-terminus of the protein swings open, allowing ions to move.

b. A short loop between domains III and IV swings open to allow sodium into the cell.

c. The S4 helices rotate, shifting the position of the S6 helices to open the ion pore.

d. A group of negatively-charged amino acids along the C-terminus rotate to open the ion pore.

e. A short loop between S4 and S5 swings open to allow sodium into the cell.

Type: multiple choice question

Title: Chapter 07 - Question 30

30. Which of the following is thought to play a role in the inactivation of potassium channels?

Feedback: Subhead: Mechanisms of Activation and Inactivation

Learning Objective: Describe two different channel structures associated with activating and inactivating ion channels.

Bloom’s Level: 3 Applying

a. Charged residues on the S4 helix

b. An inactivation gate between domains III and IV

c. A “ball” on the N-terminus of each of the channel subunits

d. A group of negatively-charged amino acids along the C-terminus

e. A short loop between the S4 and S5 helices

Type: multiple choice question

Title: Chapter 07 - Question 31

31. The time constant for the decay of whole-cell sodium current is different than the time course of single sodium channel inactivation. Why?

Feedback: Subhead: Activation and Inactivation of Single Channels

Learning Objective: Explain why the time course of activation and inactivation of single channels differs from that of macroscopic channels.

Bloom’s Level: 4. Analyzing

a. The sodium current depends on the probability of sodium channel activation.

b. The time course for sodium channel inactivation is longer than the sodium current.

c. The sodium current decays more slowly because of leak channels.

d. The sodium current decay depends on the time course of sodium channel inactivation.

e. The sodium current decays more rapidly as more sodium channels inactivate.

Type: multiple choice question

Title: Chapter 07 - Question 32

32. When is a sodium channel most likely to open following a depolarizing stimulus in the neuron?

Feedback: Subhead: Activation and Inactivation of Single Channels

Learning Objective: Explain why the time course of activation and inactivation of single channels differs from that of macroscopic channels.

Bloom’s Level: 2. Understanding

a. 100 milliseconds

b. 10 milliseconds

c. 4-6 milliseconds

d. 1-2 milliseconds

e. <1 millisecond

Type: multiple choice question

Title: Chapter 07 - Question 33

33. When is a potassium channel most likely to open following a depolarizing stimulus in the neuron?

Feedback: Subhead: Activation and Inactivation of Single Channels

Learning Objective: Explain why the time course of activation and inactivation of single channels differs from that of macroscopic channels.

Bloom’s Level: 2. Understanding

a. 100 milliseconds

b. 10 milliseconds

c. 4-6 milliseconds

d. 1-2 milliseconds

e. <1 millisecond

Type: multiple choice question

Title: Chapter 07 - Question 34

34. What is the approximate mean open time for a voltage-gated sodium channel?

Feedback: Subhead: Activation and Inactivation of Single Channels

Learning Objective: Explain why the time course of activation and inactivation of single channels differs from that of macroscopic channels.

Bloom’s Level: 2. Understanding

a. 100 milliseconds

b. 10 milliseconds

c. 5 milliseconds

d. 2 milliseconds

e. <1 millisecond

Type: multiple choice question

Title: Chapter 07 - Question 35

35. Which of the following ion conductances is responsible for the afterhyperpolarizing potential?

Feedback: Subhead: Afterpotentials

Learning Objective: Explain what afterhyperpolarizing potentials (AHPs) are and why they occur.

Bloom’s Level: 2. Understanding

a. Sodium conductance

b. Potassium conductance

c. Chloride conductance

d. Cadmium conductance

e. Magnesium conductance

Type: multiple choice question

Title: Chapter 07 - Question 36

36. What is the role of Calcium-dependent potassium channels in action potential dynamics?

Feedback: Subhead: Afterpotentials

Learning Objective: Explain what afterhyperpolarizing potentials (AHPs) are and why they occur.

Bloom’s Level: 5. Evaluating

a. They allow potassium to leave the cell during the falling phase of the action potential.

b. They allow potassium to enter the cell during the falling phase of the action potential.

c. They decrease potassium conductance, causing a return to the resting potential.

d. They increase potassium conductance, causing a slow afterhyperpolarizing potential.

e. They decrease the length of the relative refractory period following an action potential.

Type: multiple choice question

Title: Chapter 07 - Question 37

37. Spike frequency adaptation is mediated by a(n)

Feedback: Subhead: Afterpotentials

Learning Objective: Explain what afterhyperpolarizing potentials (AHPs) are and why they occur.

Bloom’s Level: 3. Applying

a. increase in sodium conductance with repeated action potentials.

b. decrease in sodium conductance with repeated action potentials.

c. increase in potassium conductance with repeated action potentials.

d. decrease in potassium conductance with repeated action potentials.

e. decrease in the availability of sodium channels with repeated action potentials.

Type: multiple choice question

Title: Chapter 07 - Question 38

38. The transport rate of the sodium-potassium cotransporter increases as

Feedback: Subhead: Afterpotentials

Learning Objective: Explain what afterhyperpolarizing potentials (AHPs) are and why they occur.

Bloom’s Level: 2: Remembering

a. intracellular sodium concentration increases.

b. extracellular sodium concentration increases.

c. intracellular potassium concentration increases.

d. extracellular potassium concentration increases.

e. the transport rate does not change with ion concentration.

Type: multiple choice question

Title: Chapter 07 - Question 39

39. Which of the following is true regarding the role of calcium on action potentials?

Feedback: Subhead: The Role of Calcium in Excitation

Learning Objective: Discuss two roles that calcium channels play in the membranes of nerve and muscle fibers.

Bloom’s Level: 3. Applying

a. The magnitude of the action potential depends on calcium concentration.

b. Extracellular calcium concentrations set the time constant for action potential decay.

c. The falling phase of the action potential is calcium-dependent in some cells.

d. The afterhyperpolarizing potential is shorter with increased extracellular calcium.

e. The rising phase of the action potential is calcium-dependent in some cells.

Type: multiple choice question

Title: Chapter 07 - Question 40

40. You perform a series of voltage-clamp experiments with 2 mM extracellular calcium, 0.2 mM extracellular calcium and 0 mM extracellular calcium. You notice that the potassium current increases with each step. What is the origin of this increase?

Feedback: Subhead: The Role of Calcium in Excitation

Learning Objective: Explain how calcium ions affect excitability.

Bloom’s Level: 4. Analyzing

a. Decreased membrane potential

b. Increased threshold potential

c. Activation of calcium-activated sodium channels

d. Activation of calcium-activated potassium channels

e. Activation of calcium channels

Type: multiple choice question

Title: Chapter 07 - Question 41

41. Both the afterhyperpolarizing current (AHP) and the afterdepolarizing current (ADP) depend on calcium levels altering

Feedback: Subhead: The Role of Calcium in Excitation

Learning Objective: Explain how calcium ions affect excitability.

Bloom’s Level: 4. Analyzing

a. sodium conductance.

b. potassium conductance.

c. chloride conductance.

d. calcium conductance.

e. magnesium conductance.

Type: multiple choice question

Title: Chapter 07 - Question 42

42. What does the voltage clamp experiment measure?

Feedback: Subhead: The student should explain that for any set (command) voltage, the experimenter measures both the direction and the magnitude of ionic current.

Subhead: Voltage Clamp Experiments

Learning Objective: Name two features of the membrane current that the voltage clamp method can measure.

Bloom’s Level: 2. Understanding

Type: essay/short answer question

Title: Chapter 07 - Question 43

43. Briefly describe the voltage clamp experimental setup and how it works.

Feedback: The student should explain the experimental setup (see Box 7.1), including the placement of the intracellular and extracellular electrodes, and that the apparatus compares the observed membrane voltage with the command voltage, injecting current to stabilize the neuron at the set voltage.

Subhead: Voltage Clamp Experiments

Learning Objective: Describe, in general terms, the experimental arrangement for voltage clamp experiments.

Bloom’s Level: 2. Understanding

Type: essay/short answer question

Title: Chapter 07 - Question 44

44. How do changes in sodium and potassium conductance following membrane depolarization lead to an action potential?

Feedback: The student should answer that the first change is a large increase in the sodium conductance, caused by voltage-gated sodium channel opening. As a result of this increase in conductance, sodium ions flow into the cell, which further depolarizes the membrane potential. This effect is regenerative as more sodium channels are activated and more sodium flows into the cell. A delayed increase in potassium conductance, which occurs as the sodium channels are inactivating (and sodium conductance decreases) then causes potassium ions to leave the cell, driving the membrane potential back toward the resting potential.

Subhead: Voltage Clamp Experiments

Learning Objective: Explain how the movement of sodium and potassium is involved in producing action potentials in nerve cell membranes.

Bloom’s Level: 5: Synthesizing

Type: essay/short answer question

Title: Chapter 07 - Question 45

45. You are recording from a neuron under voltage clamp to evaluate whether a new chemical “achematoxin” has any effect on the nervous system. You step the command voltage to +15 mV and find that there is a capacitative current and a robust, delayed late current. What effect, if any, do you suspect achematoxin has on neurons? Explain your answer.

Feedback: The student should answer that based on these results, achematoxin would be presumed to block voltage-gated sodium channels, because it abolishes the early current which is due to the influx of sodium through voltage-gated sodium channels. The student may also support their answer by noting that achematoxin has the same effect as TTX.

Subhead: Voltage Clamp Experiments

Learning Objective: Explain how membrane potential affects the magnitude and time course of ion currents.

Bloom’s Level: 5: Synthesizing

Type: essay/short answer question

Title: Chapter 07 - Question 46

46. Name and describe the three distinct currents that occur following the depolarization of the membrane in a voltage clamp experiment.

Feedback: The student should describe the capacitative current as an immediate and transient current, the early inward current that is short and carried by sodium ions, and the delayed, outward late current that is long-lasting and carried by potassium ions.

Subhead: Voltage Clamp Experiments

Learning Objective: Name the three distinct processes that follow depolarization of the nerve membrane.

Bloom’s Level: 2. Understanding

Type: essay/short answer question

Title: Chapter 07 - Question 47

47. Briefly, explain the significance of Hodgkin and Huxley’s finding that the time-course of potassium conductance could be modelled mathematically by an exponential function raised to the 4^th power.

Feedback: The student should answer that this result suggested that potassium channel activation must involve the coordinated action of four independent events, predicting the tetrameric subunit nature of the potassium channel.

Subhead: Quantitative Description of Sodium and Potassium Conductances

Learning Objective: Discuss the value of Hodgkin and Huxley’s work that mathematically described sodium and potassium conductances.

Bloom’s Level: 5: Synthesizing

Type: essay/short answer question

Title: Chapter 07 - Question 48

48. Describe the “gating currents” and their physiological source.

Feedback: The student should answer that the gating currents are the first currents seen in a voltage clamp experiment, that they are asymmetrical (appearing only with membrane depolarization, not hyperpolarization), and that they represent the movement of charged residues in the sodium channels as they translocate within the cellular membrane.

Subhead: Gating Currents

Learning Objective: Explain what gating currents are.

Bloom’s Level: 5: Synthesizing

Type: essay/short answer question

Title: Chapter 07 - Question 49

49. Identify and describe the molecular mechanism responsible for sodium channel activation.

Feedback: The student’s answer should include a description of the charged residues on the S4 helix that rotates 180° in the membrane after membrane depolarization, and how this rotation, through a link with the S6 helix, causes the pore of the channel to open.

Subhead: Mechanisms of Activation and Inactivation

Learning Objective: Describe two different channel structures associated with activating and inactivating ion channels.

Bloom’s Level: 4. Analyzing

Type: essay/short answer question

Title: Chapter 07 - Question 50

50. Describe the molecular mechanism of sodium channel inactivation, including experimental evidence supporting this mechanism.

Feedback: The student’s answer should describe the 45-residue sodium channel inactivation gate that lies between domains III and IV in the channel protein seems to serve as a hairpin inactivation gate, that targeted mutations to three amino acids in the middle of this loop abolish inactivation, and two additional regions (groups of glycine and proline residues) serve as the “hinge” for the gate.

Subhead: Mechanisms of Activation and Inactivation

Learning Objective: Describe two different channel structures associated with activating and inactivating ion channels.

Bloom’s Level: 5. Evaluating

Type: essay/short answer question

Title: Chapter 07 - Question 51

51. What is the molecular mechanism responsible for potassium channel inactivation? Support your answer with experimental evidence.

Feedback: The student’s answer should describe the “ball-and-chain” configuration that comprises the N-terminus of the channel subunits, and support this with experimental observations that targeted removal of this feature abolishes inactivation, and that adding a synthetic peptide matching the first 20 amino acids of this chain to the cytoplasm restores inactivation.

Subhead: Mechanisms of Activation and Inactivation

Learning Objective: Describe two different channel structures associated with activating and inactivating ion channels.

Bloom’s Level: 5. Evaluating

Type: essay/short answer question

Title: Chapter 07 - Question 52

52. Compare the time course of individual sodium channel opening and sodium current in the whole cell following membrane depolarization, and explain any differences between them.

Feedback: The students answer should include a comparison between sodium channel kinetics (short mean open time, immediate inactivation) and the sodium current (brief rise time, slow decay). Students should note that the sodium current is the summation of channel opening, and as such represents the probability distribution of sodium channel opening following membrane depolarization.

Subhead: Activation and Inactivation of Single Channels

Learning Objective: Explain why the time course of activation and inactivation of single channels differs from that of macroscopic channels.

Bloom’s Level: 5: Synthesizing

Type: essay/short answer question

Title: Chapter 07 - Question 53

53. What is the afterhyperpolarizing potential (AHP), and what is the ionic basis for it?

Feedback: The student’s answer should describe the AHP as a period of time following the action potential that the membrane is hyperpolarized with respect to the resting membrane potential. The student should go on to explain that an influx of calcium during the action potential leads to the opening of calcium-activated potassium channel, a concomitant increase in the potassium conductance, and a resulting influx of potassium that drives the membrane potential closer to its equilibrium potential than it is at rest.

Section: Afterpotentials.

Learning Objective: Explain what afterhyperpolarizing potentials (AHPs) are and why they occur.

Bloom’s Level: 3. Applying

Type: essay/short answer question

Title: Chapter 07 - Question 54

54. What is frequency adaptation, and what is the mechanism by which it occurs?

Feedback: The student should answer that frequency adaptation is seen when a long-lasting depolarization initiates a train of action potentials in a cell, which progressively decreases in frequency and eventually stops. This occurs because the train of action potentials leads to a steady increase in intracellular calcium, an increased activation of calcium-activated potassium channels, and a resultant increase in potassium conductance.

Subhead: Afterpotentials.

Learning Objective: Explain what afterhyperpolarizing potentials (AHPs) are and why they occur.

Bloom’s Level: 3. Applying

Type: essay/short answer question

Title: Chapter 07 - Question 55

55. In an experiment, Hodgkin and Huxley demonstrated that a hyperpolarizing prepulse potential increased sodium conductance by up to 70%, but a depolarizing prepulse potential decreased sodium conductance, with a depolarization to -25 mV resulting in virtually zero sodium conductance. What does this experiment demonstrate?

Feedback: The student should answer that this experiment shows that sodium channels exhibit some degree of inactivation even at resting membrane potentials. The hyperpolarizing prepulses served to remove this inactivation, while depolarizing prepulses exacerbated it.

Subhead: Afterpotentials.

Learning Objective: Explain what afterhyperpolarizing potentials (AHPs) are and why they occur

Bloom’s Level: 5. Evaluating

Type: essay/short answer question

Title: Chapter 07 - Question 56

56. How does extracellular calcium affect neuronal excitability?

Feedback: The student should answer that extracellular calcium concentration is inversely related to neuronal excitability; thus, when extracellular concentrations of calcium are high, neuronal excitability is low, and low calcium concentrations lead to more excitable neurons. Experimental evidence to this effect comes from Hodgkin and Huxley, who found that when extracellular calcium is reduced by five-fold, the action potential threshold is reduced by 10 to 15 mV.

Subhead: The Role of Calcium in Excitation

Learning Objective: Explain how calcium ions affect excitability.

Bloom’s Level: 3. Applying