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BIOL155 > NS - Membrane Potential: RMP, Graded and some AP > Flashcards

NS - Membrane Potential: RMP, Graded and some AP Flashcards

1
Q

True or False: Only excitable cells have transmembrane potential

A

False

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2
Q

True or False: Neurons are the only excitable cells in the body

A

False

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3
Q

True or False: The transmembrane potential is created by ion pumps (such as the Na/K-ATPase)

A

False

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4
Q

True or False: Ions move across plasma membranes through ion channels according to their concentration gradient

A

False

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5
Q

True or False: When a membrane is at a permeable ion’s equilibrium potential, the ion no longer moves

A

False

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6
Q

Match the following to their correct type of transport:

  1. Co-transporters
  2. Pumps
  3. Ion channels
A
  1. Co-transporters
    - active secondary transport
  2. Pumps
    - active primary transport
  3. Ion channels
    - passive
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7
Q

What is co-transport/secondary transport?

A

one particle is moving against its gradient with the help of another molecule moving with its gradient
- does not directly use ATP

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8
Q

Ions only move according to their concentration gradients: True or False?

A

FALSE! Ions don’t actually move according to JUST their concentration gradients

The movement of the ion differs depending on whether it has a charge or not

Ions, since they have a charge, move across membranes according to their ELECTROCHEMICAL GRADIENT!

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9
Q

What is an electrochemical gradient?

A

Charged molecules will experience repulsion and attraction according to their sign

And this is known as the ELECTROCHEMICAL GRADIENT/ELECTROMOTIVE FORCES

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10
Q

How do uncharged molecules move?

A

Uncharged molecules move passively according to a DIFFUSIVE FORCE

  • a force that pushes molecules DOWN THEIR CONCENTRATION GRADIENT
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11
Q

How do charged molecules move?

A

Charged molecules such as ions are also affected by the diffusive force created by uncharged molecules moving down their concentration gradient

HOWEVER, they also experience ELECTROMOTIVE FORCES

Initially, it may look like an ion moves down its concentration gradient, but its movement relies more strongly on its electrochemical gradient (repulsion or attraction) to its surroundings

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12
Q

What is a diffusive force?

A

A force that pushes UNCHARGED molecules down their concentration gradient

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13
Q

What kind of cells have a transmembrane potential?

A

Transmembrane Potential (Vm)

ALL CELLS HAVE A TRANSMEMBRANE POTENTIAL

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14
Q

What are two types of excitable cells?

A

Neurons and myocytes (muscle cells)

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15
Q

Describe excitable cells and their transmembrane potentials at rest or when excited (Briefly)

A

Excitable cells can alter their Vm to send and/or receive signals
- involves the movement of particles down their electrochemical/concentration gradient to change the transmembrane potential

When an excitable is EXCITED, its Vm will be less negative than at rest
- exciting a cell turns the membrane potential down

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16
Q

What is a potential?

A

Potentials are signals that are sent/received when excitable cells alter their membrane potential

  • very quickly
  • rapid time scale
  • measured in millivolts and take place in milliseconds
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17
Q

What are the two types of potentials?

A

Graded potentials
Action potentials

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18
Q

What is a graded potential?

A
  • changes in membrane potential that vary in size rather than being all-or-none
  • temporary fluctuation in membrane potential
  • associated with dendrites

ex: dendrite in sensory neuron

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19
Q

What is an action potential?

A
  • transient = lasting only for a short time
  • associated with axons
  • abrupt change that is very rapid (spike)
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20
Q

What is the difference between a graded potential and an action potential?

A

Graded potentials come in varying sizes and shapes, and their size varies relative to the number of ion channels that are open
- typically associated with dendrites and cell bodies (somas)
- not able to propagate because they get weaker as they move further from the site of initial induction

Action potentials are all the same size and they function in an all-or-none manner where they either happen because the threshold amount was reached or they do not occur at all
- typically associated with axons
- are able to propagate down axons

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21
Q

How do potentials occur? What allows Vm signals to occur?

A

Vm signals occur by PROTEINS that allow IONS TO RAPIDLY CROSS THE PLASMA MEMBRANE

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22
Q

Which of the following types of transporter proteins are used in generating potentials?

  1. Ion channel (passive transport)
  2. Permease (co-transporter)
  3. ATP-powered pump (primary transport)
A
  1. ion channels
    - fastest transporters
    - involved with signals because they are the FASTEST

ONLY ION CHANNELS ALLOW ARE USED IN GENERATING POTENTIALS

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23
Q

What does the term “resting membrane potential” mean?

A
  • Any changes in membrane potential are relative/deviating from the RMP
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24
Q

What is depolarization?

A

Any potential changes that go from rest to becoming less negative

Moving away from the negative value

(more negative to less negative/more positive)

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25
Q

What is repolarization?

A

Potential changes that bring the membrane potential back to resting potential

Restoring resting potential

(less negative back to more negative)

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26
Q

What is hyperpolarization?

A

Overshooting the restoration of the resting potential

  • when the membrane potential temporarily becomes more negative than what you started with
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27
Q

All potentials (resting, graded, and action) are created by the movement of ions through _________________________________

A

All potentials (resting, graded, and action) are created by the movement of ions through DIVERSE ION CHANNELS

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28
Q

What are the two types of ion channels involved in generating potentials?

A
  1. Leak channels (ungated)
  2. Gated channels
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29
Q

How are ion channels categorized?

A

Ion channels are categorized by gating and ion selectivity

Gating = what makes them open and shut
Ion selectivity = when they are open, what can come through?

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30
Q

What are leak ion channels?

A

Gating = not gated

  • create a pathway for ions to get through
  • always open
  • passive transport
  • always providing a place for ions to leak from one place to another
  • pretty good selectivity
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31
Q

How is resting membrane potential maintained?

A

RMP is created by leak channels, which are always open

RMP arises from the unequal permeability of ions due to different leak channel abundance
(Abundance of Na+ leak channels to K+ leak channels is roughly ~1:20)

  1. Unequal permeability to ions (# of channels)
  2. Unequal distribution of ions (Na+/K+)
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32
Q

What are gated channels?

A

Gating = not automatically open
- something must happen to it in order for the channels to open

  • require GATING FACTORS to open and close the channels
  • three types of gated channels (ligand-gating, voltage-gating, mechanical-gating)
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33
Q

What are the three types of gated ion channels?

A
  1. Ligand-gated channel
  2. Voltage-gated channel
  3. Mechanical-gated channel
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34
Q

What are ligand-gated channels?

A
  • requires a ligand to bind to the channel to open it
  • molecules that bind to receptors to open channels

Ex: muscle excitation occurs when acetylcholine released from the motor neuron binds to the channel and the neurotransmitters are released

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35
Q

What are voltage-gated channels?

A
  • closed at resting potential, but if you excite the cell, the channels will open and allow ions to pass through
  • will not pass ions at rest (closed at resting potential)
  • if a potential is generated to the correct level (threshold) then these VGC will open

Ex: Sodium voltage-gated channels and potassium voltage-gated channels

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36
Q

What are mechanical-gated channels?

A
  • requires mechanical pressure to make the channels open
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37
Q

Why are ion channels the only channel that can generate/pass ions in potentials?

A

Only ion channels are FAST ENOUGH to produce potentials/pass ions

38
Q

What is the distribution of ions outside and inside the plasma membrane?

A

K+ in abundance INSIDE (ICF)
Na+ in abundance OUTSIDE (ECF)

The ratio of Na+ to K+ leak channels in the plasma membrane is ~1:20

39
Q

What happens when K+ moves out of the cell down its concentration gradient? In an extreme example where K+ was the only permeable ion

A

At the starting state, there would be no electrical force because the charges would be balanced on both sides of the membrane, but if there was a greater abundance of K+ in the cell, the diffusive force would push K+ out of the cell

When selective K+ channels open and K+ diffuses out, a negative charge inside the cell is generated because the (+) ions have moved out and there now exists an ELECTRICAL FORCE!!

There is now a negative membrane potential

40
Q

When would K+ reach equilibrium potential? In an extreme example where K+ was the only permeable ion

A

If K+ was the only permeable ion, net K+ movement would cease when its two opposing forces (diffusive and electrical) are balanced or equal and opposite

  • when the forces on an ion are balanced, it moves inward and outward at the same rate
  • ions are still moving but there is no net movement of ions
  • still moving and still going through channels, but movement is equal
41
Q

What is equilibrium potential?

A

When there is no net movement in Vm because the ion’s electrical and diffusive forces are equal and opposite (balanced)

EQUILIBRIUM !!
- becomes so negative or positive to the point where it just gets steady because the electrical force is equal to the diffusive force

42
Q

At equilibrium potential, there is ________________ movement of ions because there is _______________ force on the ion

A

At equilibrium potential, there is NO NET movement of ions because there is NO NET force on the ion

43
Q

What is resting potential for a cell?

A

-70mV

44
Q

What is equilibrium potential for K+ in a myofiber?

A

-90mV

ions are always trying to get the membrane potential value back to its equilibrium potential

  • K+ desire to move the membrane potential to -90mV
45
Q

If we were at -70mV, what direction would K+ want to move to achieve equilibrium potential?

A

K+ would want to move out of the cell to make the inside membrane potential more NEGATIVE - bring it down to -90mV

46
Q

When do ions want to move towards their equilibrium potential?

A

At any value of Vm other than the equilibrium potential for an ion, there will be a net force on that ion (a small or large electrochemical gradient) to makes the ion move so that the membrane potential becomes closer to its equilibrium potential

47
Q

*Will the equilibrium potential for sodium be positive or negative based on its concentration gradient?

A

There is a smaller gradient for Na+, but since there is a large abundance of Na+ outside of the cell, they have a tendency to move INTO the cell down their concentration gradient

As they carry a positive charge, they bring an excess positive charge into the cell as well

When sodium moves inwards, there is an electrical gradient that is created moving outwards… Eventually sodium reaches an equilibrium potential

But now that there are more Na+ inside the cell, the membrane potential has increased to become more POSITIVE

48
Q

How would you describe the net force (electrochemical gradient) experienced by K+ and Na+ at RMP?

A

At RMP (-70mV)

K+ wants to make the membrane potential MORE NEGATIVE, so there is going to be a small electrochemical gradient moving K+ ions OUTWARDS (less net force because K+ is closer to its equilibrium potential)

Na+ wants to make the membrane potential more POSITIVE, so there is going to be a large electrochemical gradient moving Na+ ions INWARDS (big net force because it is very far from its equilibrium potential)

49
Q

Will the equilibrium potential for K+ be positive or negative?

A

For K+ in most all cells, equilibrium potential is LARGE AND NEGATIVE

-90mV

50
Q

Why isn’t resting potential equal to the equilibrium potential for K+?

A

When the neuron is at rest, K+ is the MOST permeable, but NOT the ONLY permeable ion

There are still other Na+ and Cl- ions moving, though there are fewer Na+ leaker channels in comparison to the many K+ leak channels

K+ wants to drive the membrane potential to be -90mV, ,but the other ions are simultaneously trying to get the membrane potential to their equilibrium potential, which explains why RMP is not equal to K+ equilibrium potential

51
Q

What is the relative permeability for K+/Na+/Cl- at rest?

A

Relative permeability of K+ = 1.00 (1)

Relative permeability of Cl-/K+ = 0.45 (1:2)

Relative permeability of Na+/K+ = 0.05 (1:20)

52
Q

True or False: Each ion’s contribution to the membrane potential is directly proportional to its permeability

A

True

53
Q

True or False: Each permeable ion moves the membrane towards its own equilibrium potential

A

True

54
Q

What is RMP for a sensory neuron? A myofiber?

A

Sensory neuron = -70mV
Myofiber = -90mV

55
Q

A sensory neuron has a Vm of -70mV and a myofiber has a Vm of -90mV, what predictions might you make about the relative proportion different leak channels present in the two cell types?

A

In the myofiber, there must be a greater proportion of K+ leak channels to Na+ leak channels OR less Na+ leak channels

ratio = 1:100 instead of 1:20

which is what allows the membrane potential to be more negative

56
Q

What prediction can you make, based on the equilibrium values, about what would happen if the sensory neuron opened gated channels that were permeable to sodium?

A

Eion Na+ = +70mV
Eion K+ = -90mV
Sensory neuron RMP = -70mV

If more gated channels opened and Na+ was more permeable,

There would be an increase in Vm as the Na+ would try to move towards its equilibrium potential

The Vm would become LESS NEGATIVE !!

57
Q

What is the equilibrium potential for Na+ in a myofiber?

A

+70mV

58
Q

What maintains ion concentration differences?

A

Ion concentration differences are critical for the membrane potential and they are maintained by ACTIVE TRANSPORT (PUMPS)

Ex: Na+/K+ pump

59
Q

Differentiate the roles of passive ion channels and active transport in membrane potential

A

Ion channels are what allow for potentials to be generated because they are the fastest transporters for ions

Active transport does not do membrane potentials because they are not fast enough, instead they maintain ion concentration differences

60
Q

What maintains Na+ and K+ gradients at the plasma membrane/cell?

A

Maintained by the primary active transport pump (Na-K-ATPase pump)

Maintains a higher abundance of Na+ outside of the cell and a higher abundance of K+ inside of the cell

61
Q

What maintains Cl- gradients at the plasma membrane/cell?

A

Maintained by secondary active transport (co-transport with K+)

Equilibrium potential of Cl- = -65mV

62
Q

What is responsible for maintaining resting membrane potential?

A

The transmembrane potential is indirectly maintained by ion pumps (Na/K-ATPase pump)

Leak channels create resting membrane potential as ions leak in and out

63
Q

What drives potential signals in an excitable membrane? (Graded vs action potentials)

A

Driven by the opening and closing of gated ion channels
- gated ion channels create temporary fluctuations from RMP

Graded potentials = dendrites and cell bodies
- come in different grades, shapes, sizes, etc.

Action potentials = axons (require the right voltage gated channels to propagate)
- bigger in amplitude compared to graded potentials (more than 20mV deviation from RMP)

64
Q

What are the two types of graded potentials?

A
  1. (Post)synaptic potentials (PSPs)
  2. Receptor/generator potentials
65
Q

What determines the size of a graded potential?

A

Graded potentials have variable sizes that are affected by the number of ion channels that open

  • graded potentials have different amplitudes (different amounts of change from resting potential)
  • can be bigger or smaller depending on what caused the potential to happen
  • produce membrane potential changes from RMP for as long as the gated channels are open

Recall: Membrane potential is determined by permeability = more channels open means more permeability… A BIGGER GRADED POTENTIAL !!

66
Q

During excitation, which ions are permeable?

A

Excitation = Depolarization

  • only Na+ and K+ ions are permeable
67
Q

During inhibition, which ions are permeable?

A

Inhibition = Hyperpolarization

  • only Cl- or K+ ions are permeable
68
Q

Explain: A synaptic potential can be inhibitory or excitatory.

A

During excitation: Na+ and K+ ions are permeable
- excitation is associated with DEPOLARIZATION
- making the membrane potential more positive/less negative
- deviating from the RMP

During inhibition: K+ and Cl- ions are permeable
- inhibition is associated with REPOLARIZATION/HYPERPOLARIZATION
- making the membrane potential less positive/more negative
- restoring the RMP

69
Q

What happens to membrane potential changes as they spread away from the site where they are first induced?

A

As membrane potential changes spread away from the site where they are first induced, they get WEAKER the further they spread

70
Q

What is transmembrane current?

A

the flow of ions across the membrane

71
Q

*What is electrotonic current?

A

the flow/spreading out of membrane potentials = getting weaker as they get further from the origin

72
Q

What type of potential is used for transmitting information?

A

Action potentials are specialized membrane potential signals that can rapidly transmit long distances through an axon membrane (associated with axons)

Axons are too long to rely on graded potentials for transmitting information
- usually small and do not last long
- cannot spread out very far because they get weaker and weaker as they move away

73
Q

What is the threshold value of an action potential?

A

Action potentials are ALL OR NONE
- only generated if there is enough excitation to hit the threshold amount
- if the threshold value isn’t reached then the action potential will not happen at all

74
Q

List the four key features of action potentials

A
  1. All or none (threshold)
  2. Propagation
  3. Stereotyped dimensions
  4. All or none (refractory)
75
Q

Describe the all or none key feature of action potentials

A

The threshold value must be reached in order for the action potential to occur

If the threshold value isn’t reached (~15-20mV above the RMP) then no action potential will happen

76
Q

Describe the propagation of an action potential

A

Action potentials are able to propagate down the axons because they are an all-or-none type of potential

Graded potentials get weaker as they move further from the site of initial induction, so they cannot propagate

77
Q

Describe the all or none refractory feature of action potentials

A

The refractory period describes a period after an action potential in which another action potential cannot be generated

  • this is like a grace period for the cell
78
Q

What are the two types of voltage gated ion channels that generate action potentials?

A
  1. Voltage gated sodium channels (VGNC)
  2. Voltage gated potassium channels (VGKC)
79
Q

What are voltage-gated channels?

A

When you depolarize to about the threshold level, these voltage gated channels that didn’t allow ion channels to get through before will open and allow ions to go through

80
Q

*When do VGNCs open? When do VGKCs open?

A

VGNC open during depolarization = aid depolarization so that Na+ ions can flow into the cell and make the membrane potential more positive

VGKC open during the downhill of the depolarization curve because K+ ions open and K+ ions can flow INWARDS to balance out of the electrical gradient

81
Q

What are the two distinct gates on VGNCs?

A
  1. Activation gates
  2. Inactivation gates
82
Q

What are the two types of fates in VGNCs

A

Activation gate
Inactivation gate

83
Q

What are activation gates?

A

Activation gates are found on one side of voltage-gated sodium channels as a response to depolarization

More depolarization = more activation gates open
- open quickly and Na+ floods in quickly since more gates are open
- after a certain amount of time, activation gates close

84
Q

What are inactivation gates?

A

Inactivation gates are found on on side of the voltage-gated sodium channels

  • they start OPEN then CLOSE
  • control the movement of sodium ions after depolarization
85
Q

How do activation gates work?

A

At rest, activation gates are closed

Crossing the “threshold” amount for an axon causes a few VGNCs to open

A single open channel produces extra depolarization that causes nearby VGNCs to open

The channels eventually inactivate, closing themselves

86
Q

If either the activation gates or inactivation gates are closed, no sodium goes through. Why?

A

Activation gates = stop the flow of Na+, which in turn causes the membrane potential to stop leaving!!

87
Q

Compare and contrast VGKCs to VGNCs

A

VGKC = have only one gate (an activate gate)
VGKC = very slow at opening/closing
VGKC = only occur after a delay

The gate responds to the membrane crossing threshold, but only AFTER A DELAY (refractory period)

88
Q

The opening and closing of both types of VG channels determines….

A

The SHAPE and BRIEF DURATION of an AP reflects the opening and closing of both types of VG channels

The permeability of the membrane to both types of ions rises markedly during AP, just at slightly different times

89
Q

What type of VG channel is open/closed at each stage:

A
  1. RMP - graded potential
  2. Threshold/depolarization
  3. Repolarization
  4. AHP
  5. AHP
90
Q

Positive or Negative Feedback:

“Every VG Na+ channel that
opens leads to more
depolarization, increasing
the likelihood that more VG
channels will open”

Explain this passage

A

Because the Na+ channels opening leads to MORE DEPOLARIZATION, the action potential is accelerated or driven to completion

  • as more Na+ channels open, it causes even MORE to open
  • builds upon it
  • depolarization (Na+ channels) is an example of positive feedback
91
Q

Negative feedback:

“Every VG K+ channel that
opens leads to repolarization,
increasing the likelihood that
more VG channel activation
gates will close once again.”

Explain this passage

A

Negative feedback:

When the original stimulus is shut off by the end of the stimulus
- restores the initial conditions

  • brings back to the original condition
  • repolarization (K+ channels) is an example of negative feedback
92
Q

Describe the behaviour of voltage-gated potassium channels

A
  • They open very slowly after the suprathreshold depolarization
  • VERY SLOWLY after repolarization
  • gate responds to membrane potential crossing threshold, but only after a delay

BIOL155 (34 decks)

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