AP II

Question 1

Describe the positions of the activation and inactivation gates in sodium channels during an action potential: at rest

Answer 1

activation gate (m) is shut and inactivation gate (h) is open

Question 2

Describe the positions of the activation and inactivation gates in sodium channels during an action potential: as the membrane depolarizes

Answer 2

activation gate (m) opens as inactivation gate (h) closes 
• activation gate swings faster thanthe inactivation gate

Question 3

Describe the positions of the activation and inactivation gates in sodium channels during an action potential: at peak of action potential

Answer 3

activation gate (m) and inactivation gate (h) are open

Question 4

Describe the positions of the activation and inactivation gates in sodium channels during an action potential: as membrane repolarizes

Answer 4

activation gate (m) is closing and inactivation gate (h) is closed

Question 5

Describe the positions of the activation and inactivation gates in sodium channels during an action potential: refractory period

Answer 5

activation gate (m) and inactivation gate (h) are closed

Question 6

In most cells, the influx and efflux of potassium and sodium _______. Therefore,_______

Answer 6

• do not significantly

- many action potentials can be generated before the Na+/K+ pump is required to restore proper ion balances.

Question 7

The Na+/K+ pump

Answer 7

does not play a direct role in the generation of an action potential. Instead, the Na+/K+ pump functions to restore ion balances after many action potentials have been fired

Question 8

The number of action potentials that can be fired before Na+/K+ pump activity is required depends on

Answer 8

an axon’s surface area relative to its volume.

Question 9

An axon with a relatively small surface area compared to volume can fire _______ action potentials before pump activity is needed than an axon with a large surface area to volume ratio

Answer 9

more

Question 10

A smaller surface area to volume ratio means _______ influx or efflux per unit volume, resulting in a _______ percent change in ion concentrations.

Answer 10

• less

- smaller

Question 11

The refractory period is

Answer 11

the time after an action potential is fired during which an axon cannot fire another action potential (absolute refractory period) or requires a more extreme stimulus to fire another action potential (relative refractory period)

Question 12

Mechanism underlying the refractory period: After the axon repolarizes, which gate(s) are closed?

Answer 12

both the activation gate and the inactivation gate of the sodium channel are closed. The inactivation gate requires time to reopen before another activation potential can fire.

Question 13

Mechanism underlying the refractory period: After the axon repolarizes, what happens to the K+ channels?

Answer 13

The K+ channels are still open. K+ is still leaving the axon, which makes it more difficult to depolarize the cell

Question 14

During normal depolarization (in the absence of accommodation),_______. This allows _______

Answer 14

• the inactivation gate of the sodium channel is closing as the activation gate is opening
• sodium to rush into the axon and generate the action potential.

Question 15

With accommodation, the stimulus is applied slowly, causing the_______. As a result, _______

Answer 15

• the inactivation gate to close before the activation gate opens
• sodium cannot enter the cell and an action potential is not generated

Question 16

Accomodation refers to

Answer 16

a nerve cell’s loss of excitability as a result of applying a stimulus gradually, rather than all at once

Question 17

Threshold is

Answer 17

the membrane potential at which sodium and potassium influx and efflux, respectively, are equal. Or in other words, threshold is the membrane potential at which sodium and potassium currents are equal and opposite.

Question 18

Threshold is achieved by

Answer 18

a slight initial depolarization of the axon

Question 19

The threshold must be reached in order for _______

Answer 19

an action potential to be fired.

Question 20

Once threshold is reached,

Answer 20

the potential can either be tipped in the direction of sodium or potassium equilibrium potentials

Question 21

Because sodium channels are voltage gated, a momentary, slight influx of sodium will cause the potential to

Answer 21

tip in favor of the sodium equilibrium potential, causing more channels to open. Sodium will then rush into the cell and an action potential is generated

Question 22

An action potential is generated due to

Answer 22

depolarization of an axon caused by sodium influx.

Question 23

An action potential is an _______ mechanism because sodium channels are voltage gated.

Answer 23

explosive, positive-feedback

Question 24

An action potential is an explosive, positive-feedback mechanism because _______

Answer 24

sodium channels are voltage gated

Question 25

Once an axon is depolarized to threshold: Voltage gated sodium channels

Answer 25

begin to open

Question 26

Once an axon is depolarized to threshold: Sodium

Answer 26

moves into the cell which further depolarizes the cel

Question 27

Once an axon is depolarized to threshold: further depolarization causes

Answer 27

more voltage-gated sodium channels to open