Textbook Chapter 4: Action Potential

Question 1

irritability

Answer 1

A property where organisms respond to external stimulation

Question 2

The nucleus of the neuron

Answer 2

located within an expanded region called the cell body, which is the metabolic center of the cell and the site
where most of its material contents are manufactured

Question 3

Myelin-forming cells within the central nervous system are called

Answer 3

oligodendrocytes

Question 4

A voltage (or electric potential difference) between two points, such as the inside and outside of the plasma membrane, results when

Answer 4

there is an excess of positive ions at one point and an excess of negative ions at the other point.

Question 5

voltmeter

Answer 5

an instrument that measures the difference in charge between two points

Question 6

When a nerve or muscle cell is in an unexcited state, the membrane potential is referred to as

Answer 6

the resting potential

Question 7

Potential of -70mV and equilibrium for potassium relationship

Answer 7

As one electrode penetrates the plasma membrane of the axon in b, the potential immediately drops to (inside negative), which approaches the equilibrium potential for
potassium ions, that is, the potential that would result if the membrane were impermeable to all ions except potassium.

Question 8

The magnitude and direction of the voltage across the plasma membrane are determined by

Answer 8

the differences in concentrations of ions on either side of the membrane and their relative permeabilities

Question 9

depolarization

Answer 9

a decrease in the polarity between the two sides of the membrane

Question 10

If the stimulus causes the membrane to depolarize by only a few millivolts, say, from −70 to −60 mV……

Answer 10

the membrane rapidly returns to its resting potential as soon as the stimulus has ceased

Question 11

If, however, the stimulus depolarizes the membrane beyond a certain point, called the threshold, which occurs at about -50 mV, then …… (2)

Answer 11

• The change in voltage causes the voltage-gated sodium channels to open.
• The increased permeability of the membrane to Na+ ions and the corresponding movement of positive charge into the cell cause the membrane to reverse potential briefly becoming positive at about +40mV which approaches the equilibrium potential for Na+

Question 12

After approximately 1 ms, the sodium channels spontaneously inactivate, blocking further influx of ions. According to the prevailing view, inactivation results from

Answer 12

the random diffusion of an inactivation peptide into the opening of the channel pore

Question 13

——- triggers the opening of the voltage-gated potassium channels

Answer 13

the change in membrane potential caused by Na+ influx

Question 14

—— causes the voltage-gated potassium channels to close, which returns the membrane to its resting state

Answer 14

The large negative membrane potential

Question 15

K+ equilibrium potential

Answer 15

-80 mV

Question 16

The refractory period occurs because

Answer 16

the sodium channels that were inactivated during the initial stage of the action potential must close before they can be reopened in response to another stimulus.

Question 17

The transformation of the ion channel from the inactivated (when it stops supporting sodium influx) to the closed conformation can only occur

Answer 17

after the inactivating peptide has swung out of the opening of the pore

Question 18

Although the action potential changes membrane voltage dramatically, only

Answer 18

a minute percentage of the ions on the two sides of the membrane are involved in any given action potential.

Question 19

The striking changes in membrane potential seen in are not caused by changes ….. Rather, they are caused by …..

Answer 19

• in Na+ and K+ ion concentrations on the two sides of the membrane (such changes are insignificant).
• the movements of charge in one direction or the
  other that result from the fleeting changes in permeability to these ions.

Question 20

The energy required to create an action potential is

Answer 20

stored ahead of time by the Na+/K+-ATPase, which generates steep ionic gradients across the plasma membrane. Once that is accomplished, various ions are poised to flow through the membrane down their
respective electrochemical gradients as soon as their ion channels are opened, just like water flowing from a dam once the floodgates are released.

Question 21

The large —– that accompanies an action potential creates a difference in charge along the inner and outer surfaces of the plasma membrane. As a result…..

Answer 21

• depolarization
• positive ions move toward the site of depolarization on the outer surface of the membrane and away from that site on the inner surface

Question 22

A succession of action potentials passing down the
entire length of the neuron is without any loss of intensity. This is because

Answer 22

The depolarization accompanying the action potential is very large, the membrane in the adjacent region is readily depolarized to a level greater than the threshold value, which opens the sodium channels in this adjacent region, generating another action potential