Chapter 3

Question 1

What is the voltage clamp method and what can it measure?

Answer 1

The method allows experimenters to measure permeability changes by controlling the membrane potential.

Question 2

What is Na+ permeability dependent on?

Answer 2

Depolarization; a change resulting in a membrane potential above the threshold potential.

Question 3

What are the two clamps in the voltage clamp method and how do they help?

Answer 3

Voltage clamp: controls/clamps membrane potential at any desired level (membrane potential)
Current clamp: controls/clamps injected currents at any desired level (membrane permeability)

Question 4

Inward current involves ____ while outward current involves ____.

Answer 4

a positive ion, Na+, moving into the cell (depolarization) while outward current involves the positive ion moving out of the cell (hyperpolarization).

Question 5

During depolarization, what two currents do we see?

Answer 5

An early rapid inward current (Na+ flowing into the cell) and a delayed slow rising outward current.

Question 6

Membrane conductance is closely related to what and as such can be used interchangably?

Answer 6

membrane permeability (conductance means how well can electric charges flow in a certain path).

Question 7

Define membrane conductance:

Answer 7

the ability for ions to flow across the membrane, defined as the reciprocal of the membrane resistance (g= I/R)

Question 8

During depolarization, Na+ conductance ______ while K+ conductance

Answer 8

inactivates (decreases over time), increases over time (doesn’t inactivate the same way Na+ does).

Question 9

Do both Na+ and K+ conductance require time to active?

Answer 9

Yes, especially K+ because of the delay.

Question 10

The conductances ____ progressively as the neuron depolarizes.

Answer 10

increase

Question 11

Depolarization leads K+ to _____

Answer 11

active and leave the cell to reestablish, electrochemical equilibrium.

Question 12

Undershooting is the byproduct of ______ that leads to K+ conductance _____

Answer 12

Hyperpolarization, becoming temporarily higher than it is in resting state (higher than resting potential).

Question 13

Hyperpolarization helps K+ conductance _____

Answer 13

turn off

Question 14

Refractory period

Answer 14

following an action potential, the axon becomes refractory to further excitation for a brief period of time.

Question 15

What causes the refractory period?

Answer 15

Relatively slow time course of turning off the K+ conductance and the persistence of Na+ conductance activation. This is to help ensure that another AP doesn’t immediately go off.

Question 16

Action potential generation is an example of a positive feedback loop due to it _____

Answer 16

increasing Na+ entry, causing depolarization, and more activation of Na+ conductance, and more depolarization.

Question 17

Conduction velocity

Answer 17

the time required for electrical information to travel from one end of a neuron to another.

Question 18

What are two ways to improve passive current flow:

Answer 18

increase the diameter of the axon
insulate the axonal membrane by myelin.

Question 19

Nodes of Ranvier

Answer 19

a gap in the myelin wrapping where Voltage-gated Na+ channels are found.

Question 20

Saltatory conduction:

Answer 20

action potentials traveling down the axon “jump” from one node to the next node.

Question 21

Myelination increases _____ by insulating axonal membrane to increase passive current flow and saltatory conduction.

Answer 21

conduction velocity

Question 22

What is the main function of the nodes of ranvier?

Answer 22

The Na+ voltage gated ion channels help regenerate an action potential.