Module 3: Lecture 2

Question 1

what dictates what ion drives membrane potential?

Answer 1

the permeability
- the greater the permeability of the plasma membrane for a given ion, the greater is the tendency for that ion to drive the membrane potential toward the ion’s own equilibrium potential

Question 2

are leak channels always open?

Answer 2

yes, they are passive
- ions are always passively passing through

Question 3

what channels dictate the resting membrane permeability?

Answer 3

the leak channels

Question 4

are there more potassium or sodium leak channels?

Answer 4

more potassium leak channels
- this is why potassium can leave the cell much more than sodium can enter

Question 5

the resting membrane potential is more dictated by? why?

Answer 5

potassium. this is because more positive ions is leaving the cell than more positive ions is entering

Question 6

why is potassium more permeable at rest?

Answer 6

because there is more potassium leak channels

Question 7

what is the net resting membrane potential of a neuron?

Answer 7

usually -70mV (much closer to potassium’s membrane potential)

Question 8

how much more permeable is potassium to sodium at rest?

Answer 8

50-75 times more permeable

Question 9

the passive ion movements are responsible for how much of the resting membrane potential? what is responsible for the rest?

Answer 9

80%
- Na+/K+ pump is responsible for the other 20% (active transport)

Question 10

what can change the membrane potential?

Answer 10

ions concentration across the membrane

Question 11

what does a structure of a cell dictate?

Answer 11

its function

Question 12

what goes through very transient and rapid changes in their membrane potentials?

Answer 12

neural and muscle cells

Question 13

what can neural cells or neurons do?

Answer 13

• receive a signal
• initiative/elaborate a message
• transmit a message

Question 14

what is polarization?

Answer 14

separation of charge across the membrane
- membrane potential does NOT equal 0mV
- not static - it can rapidly change

Question 15

what is depolarization?

Answer 15

• decreasing the amount of polarization that has occurred
• less charge that is separated across the cell membrane
• the membrane is less polarized than under resting conditions
• polarization goes closer to 0mV

Question 16

what is repolarization?

Answer 16

• the membrane returns to resting membrane potential value AFTER having been depolarized

Question 17

what is hyperpolarization?

Answer 17

• increase in the magnitude of the negative potential –> membrane is more polarized than under resting conditions
• separated more charge across the membrane

Question 18

what is generated when resting potential changes?

Answer 18

electrical signals

Question 19

what are the two forms of electrical signals?

Answer 19

1. the graded potentials (short-distance signals) - very localized
2. the action potentials (over long distances)

Question 20

what is the main difference between the two electrical signals?

Answer 20

the distance they occur over

Question 21

what triggers an action potential?

Answer 21

graded potentials

Question 22

what is a graded potential?

Answer 22

• local changes in the membrane potential
• short distance signals (small areas of a cell membrane change their potential)
• graded potentials can have various magnitudes and durations

Question 23

when are mechanically gated channels going to open?

Answer 23

• in response to some sort of triggering event like a touch for example

Question 24

when we open a gated channel, does our cells become more negative or positive? why?

Answer 24

more positive because sodium can now enter (can be -50mV as opposed to -70mV)
- this causes a depolarization. we are getting less charge difference between the inside and outside of the cell

Question 25

what are the two types of triggering events of a gated channels?

Answer 25

1. chemically (usually a neurotransmitter)
2. mechanical (ex. touch)

Question 26

when a depolarization occurs in an area due to a graded potential, what is that area called?

Answer 26

the active area
- a localized area so the area around it will be the inactive area

Question 27

graded potentials can vary in both?

Answer 27

magnitude as well as duration

Question 28

a graded potential is generated where?

Answer 28

at a specific point on the plasma membrane

Question 29

what opens chemically gated ion channels?

Answer 29

they open in response to a neurotransmitter

Question 30

what is the beginning of a current?

Answer 30

the active and inactive areas have opposite charge differences across the membrane

Question 31

the direction of CURRENT flow is always designated by the direction in which?

Answer 31

the positive charges are moving

Question 32

when do inactive areas become depolarized?

Answer 32

when there is a spread of those positive sodium ions in the cell because of the graded potential previously created
- happens after gated channel closes and no more ions are enters

Question 33

what does it mean that “graded potentials are decremental”?

Answer 33

as it moves along the cell membrane, it decreases in magnitude. they are getting weaker. so it progressively decreases as it traverses along that cell membrane
- returning it back to polarization
- both dispersion among the large area or the cell and also physically leaving the cell

Question 34

what is the reason as to why graded potential is decremental?

Answer 34

• the leaking of charge-carrying ions across parts of the membrane (from leak channels)
• sodium leaves from leak channels to return back to its resting polarization

Question 35

what are action potentials?

Answer 35

changing membrane potential
- flow of ions
- brief and rapid
- large amplitude
- the membrane potential reverses: the inside becomes more positive than the outside (not simply less negative than the outside as can occur for the graded potential)
- strength is the same as when they are initiated to when they end (not decremental)

Question 36

what initiates your action potentials?

Answer 36

a graded potential can generate an action potential if it reaches a sufficient magnitude (threshold potential)
- when the threshold potential is reached from enough depolarization

Question 37

what is the threshold potential that changes a graded potential to an action potential?

Answer 37

-55 to -50mV

Question 38

when is the threshold potential reached?

Answer 38

• if there is sufficient magnitude of a stimulus
• enough sodium or enough depolarizing events occur and enough sodium enters to cell to depolarize the resting membrane from -70mV to -55 or -50mV

Question 39

what is needed to turn a graded potential into an action potential?

Answer 39

many graded potentials because they are very weak
- depolarization is slow (graded potentials) until it reaches the threshold potential of -55 to -50mV