Action Potential Lecture

Question 1

action potentials ____ proportional to the stimulus size

Answer 1

ARE NOT proportional to the stimulus size

Question 2

can action potentials act locally?

Answer 2

NO - they DO NOT act locally

Question 3

do action potentials die out with distance? attentuate?

Answer 3

NO - they do not attenuate

Question 4

T/F: you can generate LOCAL potential in any given cell

Answer 4

TRUE

Question 5

Do action potentials spread in both directions?

Answer 5

NO they do not spread in both directions

Question 6

can action potentials be generated in any given cell?

Answer 6

NO - they do not happen in many different cells

Question 7

action potentials can only be generated AND propagated in ___ and __

Answer 7

neurons (at the axon) and muscles - propagation is just as important as the generation

Question 8

what types of channels are mostly found on the axon and axon hillock

Answer 8

voltage gated channels

Question 9

what is another name for the axon hillock

Answer 9

the trigger zone

Question 10

do we have VG channels in axon or soma?

Answer 10

yes! but we just don’t have enough of them

Question 11

describe the sodium voltage gated channels

Answer 11

sodium voltage gated channels have TWO gates so it makes it a little more complicated; activation gate and the inactivation gate

Question 12

describe the potassium voltage gated channels

Answer 12

a simple gate - opened or closed

Question 13

will sodium ions pass through if the activation gate is closed and the inactivation gate is open?

Answer 13

NO - the channel is still closed

Question 14

will sodium ions pass through if the activation gate is open and the inactivation gate is closed?

Answer 14

NO - the channel is still closed

Question 15

how do we open the sodium voltage gated channel

Answer 15

BOTH the activation gate and the inactivation gate have to be OPEN for the channel as a whole to be open and for sodium ions to pass through

Question 16

at resting state: all the channels are ___

Answer 16

CLOSED; despite the fact that the inactivation gate is open on the sodium voltage gated channel; only way to move is leak channels or generating a local potential

Question 17

when do the voltage gates change their status

Answer 17

upon depolarization and ONLY after reaching a threshold

Question 18

channels will open up at a given potential - what number

Answer 18

-55 mV

Question 19

inactivation gates ___, activation gate ___ and potassium channel ____ after reaching threshold

Answer 19

inactivation gate closes, activation gate opens and potassium channel opens

Question 20

sodium activation gate is a ___ gate and the sodium inactivation gate is a ___ gate ; the potassium gate is a ____ gate

Answer 20

fast, slow, slow; 0.5 ms delay that occurs with the slow closing gates that allows the sodium channel to be open

Question 21

4 step graph for action potential

Answer 21

1. all channels are closed at resting membrane potential - (the sodium inactivation gate is open but it doesn’t matter)
2. stimulus added and the channel opens and sodium ions move in
3. Depolarization ; -70 become -68 - (local graded potential)
4. Eventually threshold is reached if we have enough sodium ions
5. inactivation gates close really slowly and activation gates open really fast, so sodium channel is OPEN for a small amount of time
6. increasing on the depolarization (2) event as more ions move in (positive feedback chain)
7. peak of depolarization is reached when the inactivation gates finally CLOSED
8. repolarization (3) potassium gates are finally opened up, so potassium leaves and cell is losing positive charge and is repolarizing
9. undershoot beyond -70 (hyperpolarization) is caused by the slow closing of the potassium channels to close completely
10. go back to resting membrane potential - SPP restores the gradient and resting membrane potential

Question 22

T/F: action potential starts with a local graded potential

Answer 22

true

Question 23

once the first sodium voltage gated channel is open why can the stimulus go away?

Answer 23

because a positive feedback loop is started and each VG channel opens the next one

Question 24

when does depolarization stop

Answer 24

when the inactivation gate finally closes and as a result closes the channel

Question 25

atrocytes will help absorb excess potassium ions and help restore the membrane potential

Answer 25

TRUE