Lecture 2: Graded and Action Potentials

Question 1

the membrane potential outside a cell is assumed to be ___mV and is referred to as __

Answer 1

zero; ground

Question 2

the inside membrane potential of a cell is measured relative to what value?

Answer 2

ground (0mV)

Question 3

what happens in the depolarization phase of a membrane potential?

Answer 3

na channels open and na rushes in

Question 4

during depolarization, the inside of the cell becomes more __(+/-)

Answer 4

+

Question 5

what happens in the repolarizing/hyperpolarizing phases of a membrane potential?

Answer 5

na channels are inactivated then closed and K channels are open and K flows out

Question 6

what causes a graded potential?

Answer 6

stimuli that activate VG ion channels causing the cell membrane to become more permeable to certain ions

Question 7

give 3 examples of stimuli that can cause a graded potential

Answer 7

1. applied pressure
2. binding of acetylcholine
3. binding of glycine

Question 8

graded potentials are proportional to the ___ of the stimulus

Answer 8

strength

Question 9

why does a stronger stimulus produce a greater graded potential?

Answer 9

causes more ion channels to be opened

Question 10

graded potentials are produced at the ___ site, they can spread __ distances

Answer 10

local stimulus; very short

Question 11

the spread of a graded potential is caused by __

Answer 11

local current flow / local redistribution of charge

Question 12

t/f graded potentials are good at travelling long distances

Answer 12

false

Question 13

along with strength, graded potentials are also sensitive to the __ of stimuli

Answer 13

frequency

Question 14

if a second stimuli is added to a graded potential before it ends, what is the effect on depolarization?

Answer 14

increases (piggy back)

Question 15

describe the depolarization in an action potential

Answer 15

large and brief/fast

Question 16

action potential is initiate by depolarization beyond __

Answer 16

threshold

Question 17

what type of membrane potential is used for long-distance signalling

Answer 17

action potential

Question 18

what must happen for a graded potential to become an action potential?

Answer 18

a stimuli must be great enough to result in a graded potential that depolarizes the membrane to threshold

Question 19

what is the typical threshold of a nerve cell?

Answer 19

-50mV

Question 20

what is the resting membrane potential of a nerve cell?

Answer 20

-70mV

Question 21

t/f VG ion channels are different from background “leak” channels

Answer 21

true

Question 22

what causes activation of VG ion channels?

Answer 22

changes in membrane potential (depolarization)

Question 23

Na channels are ____ (fast/slow) and ___ (transient/sustained)

Answer 23

fast and transient

Question 24

K channels are ____ (fast/slow) and ____ (transient/sustained)

Answer 24

slow and sustained

Question 25

during an action potential, permeability to Na is __

Answer 25

high

Question 26

describe the 4 steps of an action potential

Answer 26

1. all channels are closed (rest)
2. graded potential depolarization to threshold results in opening of Na channels which accelerates depolarization
3. na channels are inactivated and K channels open, causing K to rush out, making the cell more negative (repolarization)
4. after hyper polarization sodium channels are now closed and K channels remain open until resting is returned

Question 27

transient increase in __ results from na channel inactivation

Answer 27

na conductase

Question 28

do potassium channels require inactivation?

Answer 28

no

Question 29

t/f action potential are all or none

Answer 29

true

Question 30

why are action potentials all or none?

Answer 30

once threshold is met and those sodium ions rush in, all the steps must follow to restore resting potential

Question 31

a bigger stimulus would generated ___ action potential

Answer 31

multiple

Question 32

t/f a stronger stimulus results in bigger action potential

Answer 32

false

Question 33

the absolute refractory period begins ___ and ends ___

Answer 33

when na channels open; when na channels recover from inactivation

Question 34

the relative refractory period occurs when

Answer 34

na channels are closed and K channels are still open, but resting has not been returned

Question 35

t/f during the absolute refractory period it is impossible to generate another action potential

Answer 35

true

Question 36

t/f during the relative refractory period it is unlikely but possible for another action potential to be generated

Answer 36

true

Question 37

why is it harder to start a new action potential during the relative refractory period?

Answer 37

b/c the baseline is lower due to hyper polarization so the depolarization needs to be larger to reach threshold