Introduction to the Action Potential

Question 1

The

separation of charges makes each cell a

Answer 1

battery

Question 2

the cells’ resting potential is a power source that generates

Answer 2

action potentials

Question 3

are proteins in the cell membrane that confer permeability to ions

Answer 3

Ion channels

Question 4

K+

channels are always open regardless of membrane potential. t/f

Answer 4

True

Question 5

channels that are gated (opened and closed) by the membrane potential

Answer 5

voltage gated ion channels

Question 6

Two types of voltage gated ion channels generate action potentials. Please enumerate

Answer 6

voltage gated

sodium channel and the other is a voltage gated potassium channel.

Question 7

three main

features of the channel (voltage gated sodium channels)

Answer 7

1. central pore that is selectively permeable to Na+ ions;
2. activation gate
3. inactivation gate

Question 8

hat is closed at the resting potential

but is opened by depolarization (when the inside of the cell becomes less negative than rest);

Answer 8

voltage gated Na channel - activation gate

Question 9

Na channel that is open at rest but is closed by

depolarization.

Answer 9

inactivation gate

Question 10

inactivation gate is also referred to as a

Answer 10

“ball and chain”

Question 11

has a structure such that a length of amino acids forms a chain-like structure that is linked to
another group of amino acids that forms a ball-like structure.

Answer 11

inactivation gate

Question 12

when neurons are at

rest, at about -70 mV, what is the status of voltage gated Na channels

Answer 12

activation gate is closed and the inactivation is open.

Question 13

The whole
idea of depolarization is to
(status of voltage gated Na channels )

Answer 13

open the activation gate and close the inactivation gate

Question 14

However,
an important feature of the two gates is that when the axon is depolarized, the opening of the
activation gate is just slightly faster than the

Answer 14

closing of the inactivation gate

Question 15

After the activation gate has been open for about ___, the slower inactivation gate
swings shut, thereby plugging the pore and preventing the further influx of Na+ ions into the cell.

Answer 15

1.0 ms

Question 16

as a selflimiting

gate that allows the pore to be open for only about a 1.0 ms and no longer.

Answer 16

inactivation gate

Question 17

membrane just under the open Na channel will approach this potential

Answer 17

sodium equilibrium potential, ENa,

Question 18

sodium equilibrium potential, ENa, which is about

Answer 18

+55 mV (inside positive).

Question 19

during depolarization, this brief period of less than 1.0 ms (1/1000 of a second); the
membrane potential spikes from a resting value of -70 mV to +55 mV, a net change of

Answer 19

125

mV

Question 20

This spike in the membrane potential, from -70 to +55 mV, is what comprises the ___ of action potential

Answer 20

upstroke

Question 21

is a stereotyped event

that is triggered by depolarization of the membrane

Answer 21

action potential, or spike

Question 22

Typically the first depolarization that starts the entire cycle is due to the influx of positive
charges caused by the release of transmitter at the synapse. But once the spike or action
potential is first initiated at the axon hillock, it is reproduced over and over again at each
point along the axon, because of the presence of what structure

Answer 22

voltage gated sodium channels

Question 23

The rapid re-polarization of the membrane

potential is accomplished by the

Answer 23

opening of voltage-gated potassium channels- efflux of K+ ions.

Question 24

their

purpose is for the rapid efflux of positive charges from the inside of the cell to the outside.

Answer 24

voltage gated potassium channels

Question 25

The reason that positive charges can be carried in by one ion (Na+) and removed by another ion (K+) is that the opening (or closing) of channels depends ONLY on the

Answer 25

charge inside the membrane

Question 26

VOLTAGE GATED CHANNELS | OPERATE THOUGH

Answer 26

EQUAL OPPORTUNITY” CHARGES they care only about charge and are oblivious to whether the charge was carried by K+, Na +, or Ca++ ions

Question 27

Na+ channels open

Answer 27

upstroke

Question 28

downstroke

Answer 28

Na+ inactivation gates are closing | K channels are opening

Question 29

Only K+ channels are open. membrane is at Ek

Answer 29

undershoot

Question 30

both Na and K are closed

Answer 30

RM

Question 31

begins less than 1.0 ms after the activation gates open.

Answer 31

Repolarization

Question 32

because of the massive increase in potassium permeability, the axonal membrane at that location approaches the potassium equilibrium potential, EK. This phase of the action potential is called

Answer 32

the undershoot,

Question 33

for that brief period the membrane potential is even | more negative than the resting potential.

Answer 33

the undershoot,

Question 34

sets an upper limit on the rate at which action potentials can be produced.

Answer 34

refractory | period

Question 35

Since the | refractory period is about

Answer 35

about 1.0 ms,

Question 36

highest possible firing rate of any neuron is

Answer 36

1000 | spikes/sec.

Question 37

is an all or none event and has a threshold

Answer 37

action potential

Question 38

When an action potential occurs, it always drives the membrane potential to

Answer 38

+55 mV.

Question 39

However, depolarizations are graded | and can be small or large or have any value in between. T/F

Answer 39

True

Question 40

Neurons, however, need a certain level of | depolarization to evoke an action potential, called the

Answer 40

“threshold level”.

Question 41

Rather, the depolarization | needed to generate an action potential is produced by the

Answer 41

opening of many sodium channels at | the same time.

Question 42

There is a range of small depolarizations where the Na+ entry into the cell, while increased over resting, will still be less than the exit of K+ ions from the cell. This range of depolarizations is referred to as being

Answer 42

“subthreshold”

Question 43

no action potentials are evoked by these small depolarizations.

Answer 43

“subthreshold

Question 44

The additional depolarization, caused by the slightly greater influx of Na+ than efflux of K+, will then open a few more Na+ channels that will bring in more Na+ and initiate the

Answer 44

positive feedback

Question 45

net result of positive feedback is

Answer 45

rapid, nearly simultaneous opening of many sodium channels that drives the membrane potential to the sodium equilibrium potential, ENa, which is an action potential.

Question 46

if the cell reaches a depolarization where the entry of Na+ is exactly equal to the exit of K+, and if, in the next instant one more K+ leaves the cell than Na+ enters, the membrane potential will begin to return to the

Answer 46

resting value.

Question 47

that value of membrane potential at which the | Na+ current entering the cell just exceeds the K+ current leaving the cell.

Answer 47

threshold

Question 48

threshold For most neurons this is in the range

Answer 48

10 to 15 mV depolarized from rest