Membrane Potential Lecture

Question 1

ion channels

Answer 1

the door which ions can move in or out

Question 2

there are 4 types of ion channels

Answer 2

1. Leak channels
2. Chemically (Ligand) gated channels
3. Voltage gated channels
4. Mechanically gated channels

Question 3

what is a leak channel

Answer 3

they are always open; BUT not everything can move through the channel - still very specific; size and charge matters - sodium cant move through potassium leak channels and vice versa

Question 4

what drives ions to move in or out of the membrane

Answer 4

the electrochemical gradient - higher concentration of certain ions on the outside versus inside

Question 5

always go from ___ to ___ gradient when ions move

Answer 5

higher to lower area

Question 6

ions have charges which is why the driving force is called the _______ gradient

Answer 6

electrochemical - electrical AND chemical ; the combination of the two

Question 7

there is a ___ concentration of potassium K+ in the cytosol than in the ECF

Answer 7

HIGHER inside the cell than it is outside the cell

Question 8

will the CHEMICAL gradient drive K+ in or out of the cell

Answer 8

OUT - wants to go from higher to lower concentration

Question 9

how is K+ going to leave the cell

Answer 9

through K+ leak channels

Question 10

where does the majority of the negative charge in the inside of cell come from?

Answer 10

the negatively charged proteins that are inside the cell - not from the negative N ions

Question 11

the plus potassium and negatively charged proteins are ___ nicely so why does K+ want to move out

Answer 11

balanced ; they want to move because of the CHEMICAL gradient

Question 12

what happens when potassium leaves the cell and proteins stay in?

Answer 12

more of an electrical gradient, and the more K+ that leaves the cell and tries to solve the CHEMICAL the greater the ELECTRICAL gradient becomes

Question 13

so as K+ leaves to go be with other K+s there is now a force calling them ____ to the cell

Answer 13

back to the cell ;

Question 14

the more potassium that leaves, the more ___ that will want to come back into the cell

Answer 14

potassium

Question 15

in the tug of war between electrical and chemical - who wins

Answer 15

usually the chemical wins out

Question 16

we decided that the measure membrane potential by measuring the inside of the cell and comparing it to the outside

Answer 16

cytosol compared to ECF

Question 17

what would the electrical membrane potential that will counteract the outflow of K+

Answer 17

it will be more negative relative to the outside, so the answer is negative

Question 18

what is reversal potential

Answer 18

the reversal potential of a given ion is the membrane potential at which the net flow of the ion across the membrane = 0

Question 19

how does reversal potential happen

Answer 19

this happens when the electrical gradient has become as strong as the chemical gradient so that there is still flow of an ion in/out of the cell, but they are flowing in/out at the same rate, meaning the NET FLOW is 0

Question 20

T/F: each ion has its own reversal potential and is completely independent of other reversal potentials

Answer 20

true

Question 21

does permeability have anything to do with reversal potential

Answer 21

nope

Question 22

Synonyms for reversal potential

Answer 22

Nerst equation and equilibrium potential

Question 23

reversal potential is NOT the resting membrane potential

Answer 23

TRUE

Question 24

sodium is found in higher concentrations on the ___ of the cell compared to the ___ of the cell

Answer 24

higher Na+ concentrations outside of cell (in ECF) than inside the cell (in cytosol)

Question 25

the CHEMICAL gradient will drive Na+ ___ the cell

Answer 25

inside

Question 26

what will the electrical reversal potential be to counteract the Na+ flow

Answer 26

it has to be positive because it was negative then the Na+ ion would WANT to stay - positive rejects positive, so we need positive to PUSH Na+ out of the cell

Question 27

what is resting membrane potential

Answer 27

it is the membrane potential of a given membrane when there is no stimulus and all the gated channels are closed

Question 28

Na+ and K+ are the two major ions that contribute to membrane potential - so what is numeric resting membrane potential

Answer 28

-70 mV ; puts together -88 mV and 60 mV

Question 29

T/F : sodium barely has an effect on the resting membrane potential value of -70mV

Answer 29

True - sodiums membrane potential is positive 60 mV and RMP is -70mV

Question 30

why does sodium not contribute as much to the resting membrane potential ; why is the value so close to potassium’s value?

Answer 30

the membrane is not as permeable to sodium as it is to potassium ; a much lower concentration of sodium leak channels than potassium leak channels - not many windows in the wall for sodium, but lots for potassium

Question 31

resting membrane potential is mainly dependent on the potassium electrochemical gradient and it is ___

Answer 31

negative

Question 32

concentration is not changed by much in order to affect the potential - T/F?

Answer 32

True - think about the beach analogy - sand in eye is super bothersome but only one grain from a beach of millions left the sand

Question 33

what would happen if there wasn’t a gradient

Answer 33

ions wouldn’t want to move

Question 34

what creates the gradient in the first place? what causes the difference in the concentrations of ions?

Answer 34

the sodium - potassium pump; the hardest working protein in our body ; it actively (requires ATP) working against the concentration gradient - it throws sodium out and throws potassium in - important for creating AND maintaining the gradient

Question 35

how does sodium potassium pump maintain the resting potential

Answer 35

it will bring gradient back to normal / maintain resting membrane potential

Question 36

in reality not a huge amount of ions flow T/F

Answer 36

True - 0.006% of K+ ions move

Question 37

T/F: The membrane is much more permeable to K+ than to Na+

Answer 37

True.

Question 38

T/F: the electrical gradient counteracts the chemical gradient and the ions reach equilibrium (NET FLOW = 0)

Answer 38

True.

Question 39

T/F: The Na+/K+ pump maintains the chemical gradient and is essential in creating/maintaining a negative resting membrane potential

Answer 39

True.

Question 40

what is a chemically (ligand) gated channel

Answer 40

they are opened by ligand which is a compound/chemical they can be ion-specific or not ion specific (in terms of permeability) but they ARE SPECIFIC to the ligand that binds to receptor and opens the channel (ex. the Ach receptor at the neural muscular junctions is permeable to both Na+ and K+)

Question 41

what is a voltage-gated channel

Answer 41

they open or close depending on the voltage/potential surrounding them; a change in the voltage (membrane potential) is what stimulates it to open/close; they are ion selective channels ; their gates can open and close at different speeds;

Question 42

what are mechanically gated channels

Answer 42

carousels in ears are mechanically gated channels - they are found in sensory receptors (ex. in ears we have stream of fluid that is pushing those hairs and opening mechanically gated channels and as a result ions move in)

Question 43

how do the three gated channels differ?

Answer 43

they differ in how they respond to a stimulus

Question 44

in resting membrane potential it is ___

Answer 44

negative

Question 45

we can change membrane potential by changing the gate’s status through ___

Answer 45

polarization

Question 46

depolarize

Answer 46

making the cell less polarized or closer to 0 (ex. -70 to -60)

Question 47

hyperpolarize

Answer 47

making it further away from 0 (ex. -70 to -90)

Question 48

how do we polarize ?

Answer 48

with a stimulus - electrical, chemical or mechanical

Question 49

what happens to little amount of sodium coming through leak channels

Answer 49

it gets booted back out by SPP

Question 50

what is a local or graded potential?

Answer 50

a short-range change (ex. -70 to -65) in a membrane potential upon a stimulus (ex. ligand gated channels opening and positive sodium ions moving into the cell leading to depolarization)

Question 51

sodium ligand gated channels opening upon stimulus leads to ___ of the cell

Answer 51

depolarization

Question 52

T/F: adding ions outside the membrane changes the electrical gradient

Answer 52

FALSE - you changed the CHEMICAL gradient but not the electrical gradient (remember the beach example)

Question 53

can the graded/local potential be increased? HOW?

Answer 53

YES! A local potential can be increased with a stronger stimulus (as in the Ach - not the ions that are already there for a ligand channel)

Question 54

if I add a bunch of sodium and did not open the ligand gated channels will it affect the resting membrane potential

Answer 54

No - its like grains of sands to the beach ; the membrane is not very permeable to it; just a few leak channels but otherwise it cannot flow

Question 55

if I add a bunch of potassium will it affect the resting membrane potential even if the channels are closed

Answer 55

yes - more so than sodium because membrane is highly permeable to the potassium and potassium can flow easily

Question 56

is the SPP continuous

Answer 56

yes

Question 57

the stronger stimulus affects the graded potential which is why we call it a graded solution

Answer 57

TRUE

Question 58

why does a graded/local potential weaken

Answer 58

the response to the graded/local potential is diffusing/moving along the membrane because cations will move towards the negative charge to the left and right of where the local potential occured; the site next to the original depolarization site will also depolarize but not by as much because it didn’t have the same amount of influx of ions as did the original site causing it to slowly weaken

Question 59

why does a graded/local potential weaken

Answer 59

& the SPP is pumping them back out and some diffuse toward middle of cell and their effect is less; the response to the graded/local potential is diffusing/moving along the membrane because cations will move towards the negative charge to the left and right of where the local potential occured; the site next to the original depolarization site will also depolarize but not by as much because it didn’t have the same amount of influx of ions as did the original site causing it to slowly weaken

Question 60

what is an example of a stimulus that could lead to hyperpolarization

Answer 60

opening Cl- ligand gated channels (they are higher in concentration outside the cell like Na+) or opening K+ channels (they would leave the cell but they’re cations so it would lead to hyperpolarization)