Action Potential I: Generation

Question 1

Threshold is the point at which _____ and ______ currents are exactly equal and opposite.

Answer 1

sodium; potassium

Question 1

At rest, the activation gate (m) is shut and the _____ is open.

Answer 1

inactivation gate (h)

Question 2

The K+ channel gates are _____ at rest.

Answer 2

closed

Question 3

At rest, the _______ is shut and the inactivation gate (h) is open.

Answer 3

activation gate (m)

Question 3

Without the _____, the membrane would repolarize very slowly.

Answer 3

voltage-gated K+ channels

Question 4

Repolarization occurs for two reasons: 1) _____, and 2) _____.

Answer 4

P(Na) declines back to its resting level; P(K) undergoes a transient increase

Question 4

When the membrane is depolarized, the activation gate _____ and the inactivation gate closes.

Answer 4

opens

Question 4

The ____ channel behavior is an example of negative feedback.

Answer 4

K+

Question 4

What is the refractory period?

Answer 4

after generating an AP, the axon cannot produce another one for a few milliseconds

Question 5

The membrane potential must be _____ to the same level before each action potential occurs.

Answer 5

depolarized

Question 6

When the membrane is _____, the activation gate opens and the inactivation gate closes.

Answer 6

depolarized

Question 7

The action potential is always the same size and shape in that neuron, regardless of _______.

Answer 7

how big the stimulus is

Question 7

What is the absolute refractory period?

Answer 7

during this time, no stimulus, no matter how strong, can evoke another AP

Question 9

What is an action potential?

Answer 9

when the membrane undergoes a large, rapid, transient depolarization

Question 9

The threshold is not the point at which all of the ____ open.

Answer 9

Na+ channels

Question 11

Within each square micrometer of typical axonal membrane are about 100 ____ channels which, at rest, do not permit any ____ to cross the membrane.

Answer 11

sodium; Na+

Question 12

The K+ channel gates open in response to ______.

Answer 12

depolarization

Question 13

The action potential depends on the ______.

Answer 13

voltage-gated sodium channels

Question 13

The _______ depends on the voltage-gated sodium channels.

Answer 13

action potential

Question 14

The ‘passive’ electrical properties of axons are not sufficient to conduct an action potential ______.

Answer 14

over long distances

Question 15

What is the relative refractory period?

Answer 15

time during which a stronger-than-normal stimulus is required to evoke another AP

Question 16

The _____ open in response to depolarization.

Answer 16

K+ channel gates

Question 16

K+ channels close with _____.

Answer 16

a delay

Question 17

What controls the behavior of the K+ channel gate?

Answer 17

membrane potential

Question 17

Why is there a refractory period?

Answer 17

the sodium channel inactivation (h) gates require time to reopen after repolarization

Question 18

The ______ gate swings faster.

Answer 18

activation

Question 18

After \_\_\_\_\_, an axon cannot generate another one for a few milliseconds.

Answer 18

producing an action potential

Question 19

\_\_\_\_\_\_ occurs for two reasons: 1) P(Na) declines back to its resting level and 2) P(K) undergoes a transient increase.

Answer 19

Repolarization

Question 21

Without the sodium channels, electrical signals can’t spread more than _____ from the site of the stimulus.

Answer 21

a few millimeters

Question 22

\_\_\_\_ channels close with a delay.

Answer 22

K+

Question 23

The action potential is always the same _____ in that neuron, regardless of how big the stimulus is.

Answer 23

size and shape

Question 24

The K+ channel behavior is an example of ____ feedback.

Answer 24

negative

Question 26

At the beginning of depolarization, the membrane permeability is drastically altered from one that is largely permeable to _____ to one that is much, much more permeable to \_\_\_\_.

Answer 26

potassium; sodium

Question 27

The K+ channel gates ____ in response to depolarization.

Answer 27

open

Question 29

Without the \_\_\_\_\_, electrical signals can’t spread more than a few millimeters from the site of the stimulus.

Answer 29

sodium channels

Question 30

The ____ channels start conducting when the cell is depolarized a little bit.

Answer 30

Na+

Question 32

What does it mean that action potentials are all or none events?

Answer 32

the AP is always the same size and shape regardless of the stimulus

Question 34

The _____ open as the Na+ channel inactivation gates are closing.

Answer 34

K+ channels

Question 36

\_\_\_\_\_\_\_ is the point at which sodium and potassium currents are exactly equal and opposite.

Answer 36

Threshold

Question 37

The _____ is not the point at which all of the Na+ channels open.

Answer 37

threshold

Question 39

As ______ ions rush into the cell, the inside becomes more positive.

Answer 39

sodium

Question 41

What does threshold mean?

Answer 41

a certain amount of depolarization is required to initiate an AP

Question 42

As sodium ions rush into the cell, the inside becomes more \_\_\_\_\_.

Answer 42

positive

Question 43

The ____ channel gates are closed at rest.

Answer 43

K+

Question 44

When the membrane is depolarized, the activation gate opens and the \_\_\_\_.

Answer 44

inactivation gate closes

Question 45

After producing an action potential, an axon cannot generate another one \_\_\_\_\_.

Answer 45

for a few milliseconds

Question 46

The _______ is always the same size and shape in that neuron, regardless of how big the stimulus is.

Answer 46

action potential

Question 47

\_\_\_\_\_, the activation gate (m) is shut and the inactivation gate (h) is open.

Answer 47

At rest

Question 49

What does it mean that there is a threshold for excitation?

Answer 49

the membrane potential must be depolarized to the same level before each action potential occurs

Question 50

The Na+ opening is an example of ____ feedback.

Answer 50

positive

Question 51

Without the voltage-gated K+ channels, the membrane would \_\_\_\_\_.

Answer 51

repolarize very slowly

Question 52

The membrane potential must be depolarized to the same level before each _____ occurs.

Answer 52

action potential

Question 53

Why do K+ channels close with a delay?

Answer 53

to allow both maximum height of the AP and rapid repolarization