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1H06A > 04 - Membrane Potential > Flashcards

04 - Membrane Potential Flashcards

1
Q

When does potential difference occur?

A

Potential difference occurs when there is a separation of electrical charge

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2
Q

Why is it called potential difference?

A
  • The different electrical charges are attracted to each other, i.e., there is a force between them
  • This force has the potential to do work
  • There is potential energy due to the difference in the distribution of electrical charges
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3
Q

What is the potential difference that exists across all the cell membranes?

A

Membrane potential

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4
Q

What’s the potential diff measured in?

A

Volts

  • The greater the amount of charge separation, the greater the amount of volts
    Because the potential difference is very tiny we use units of millivolts (1/1000 of a volt)
  • If there is no voltage that means you’re dead
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5
Q

Why is there a small charge separation compared to the inside of a cell to the outside?

A
  • Across the plasma membrane of cells, there are different concentrations of ions (charged particles like the cations Na+, K+, Ca2+ and the anion Cl- ) as well as charges on proteins
  • There are a few more negative ions on the inside of the plasma membrane than on the outside
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6
Q

Is the cytoplasm more negative or the extracellular space?

A

The cytoplasm is more negative

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7
Q

Which direction do potassium Ions want to go?

A

K+ is always trying to leave the cell (EFFLUX) b/c K+ wants to go down its concentration gradient because it is in high concentration inside of the cell

  • When K+ leaves the cell, the potential difference becomes greater
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8
Q

Why care about potential difference?

A

They can be signals (APs)

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9
Q

Efflux meaning

A

Ions trying to LEAVE the cell

Cytoplasm to ECS

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10
Q

Are there more K+ in the cell or outside?

A

Higher [K+] in cytoplasm

Lower [K+] in ECS

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11
Q

Which direction do sodium Ions want to go?

A

Sodium ions are always trying to enter the cell (INFLUX) b/c
- Na+ “wants” to go down its concentration gradient
sodium is less concentrated inside of the cell than outside so sodium attempts to enter the cell
- Na+ wants to go down its charge gradient
the inside of the cell is negative so the positively charged sodium ions attempt to enter the cell

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12
Q

When Na+ enter the cell, is the potential difference greater or lessened?

A

When Na+ enters the cell, the potential difference is lessened (the voltage moves towards zero) because the positive charge on the sodium ions decreases the net amount of negative charge in the cell

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13
Q

What is resting membrane potential?

A

The resting potential is what is in a cell at rest

  • Every cell has a RMP
  • Inside of a neuron at rest it is about -70mV other cells are less but none are less than -40mV
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14
Q

What are the one or two forces pushing on the ions that make the RMP?

A
  • The first force is that which pushes ions down their concentration gradient (i.e., ions diffuse from areas where they are in high concentrations to areas where they are in low concentration)
  • The second force is that which pushes ions down their charge gradient (i.e., positive charges diffuse towards areas of negative charges and negative charges diffuse towards areas with positive charges)
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15
Q

Inside vs outside of a cell (+/- and what ions)

A

Inside (cytoplasm)
- More (-) protein
- More K+
- More negative

Outside (ECS)
- More Na+
- More positive

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16
Q

What causes RMP?

A

Uneven distribution of ions
- The extracellular fluid is rich in Na+ and Cl-
- The cytosol is rich in K+ and protein
- The protein molecules within the cell have a negative charge but cannot move (they help keep the inside of the cell negative)

If you add up all the charges you get a few more (just a few) negatives on the inside thus they line up on the membrane

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17
Q

What are the 2 ways to maintain the RMP?

A
  • Differentially permeable membrane
  • Sodium-potassium pump (Na+/K+ ATPase)
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18
Q

How does a differentially permeable membrane work?

A
  • The membrane is much less permeable to sodium ions than potassium ions
  • Sodium leaks into the cell much more slowly than potassium leaks out of the cell
  • As a result of the different movement of positive ions more positive charge leaks out than positive charge leaking in the cell a net negative charge is left in the cell
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19
Q

How does sodium-potassium pump (Na+/K+ ATPase) work?

A
  • The membrane is somewhat leaky (i.e., Na+ comes in and K+ goes out) so the ions have to be returned whence they came or the RMP runs down
  • Three sodium ions (3 Na+) are pumped out for every two potassium ions (2 K+) that are pumped into the cell (net negative charge is left) this is mildly electrogenic (that means it causes a wee bit of the RMP)
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20
Q

What format is the changes in membrane potential in?

A

As electrically-coded messages

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21
Q

What are the 2 types of membrane potential changes?

A

Graded potentials
Action potentials

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22
Q

How are potential changes generated?

A

By opening channels (eg. Na+ pump)

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23
Q

How are messages sent quickly?

A

They are electrically encoded

24
Q

How do voltage-gated ion channels work?

A
  1. Voltage change
  2. Voltage-gated ion channel gate opens (b/c of voltage change)
  3. Cations enter (positive ions)
  4. Potential decreases b/c of the entry of cations
  5. Voltage-gated ion channel gate close
25
Q

How do ligand-gated ion channels work?

A
  1. Ligand binds to the receptor
  2. Ligand-gated ion channel gate opens
  3. Cations enter (positive ions)
  4. Potential difference decreases b/c of the entry of cations
  5. Ligand dissociates
  6. Ligand-gated ion channel gate close
26
Q

What happens if the binding of ligand leads to the opening of Na+ channels?

A

The cell depolarizes

  • Positive ions (Na+) rush in
  • Ligand-gated Na+ channels make the potential difference less
27
Q

What happens if the binding of ligand leads to the opening of K+ channels?

A

The cell hyperpolarizes

  • Positive ions (K+) rush out
  • Ligand-gated K+ channels make the potential difference greater
28
Q

Are graded potentials long lived or short lived?

A

Short-lived

  • Brought back to homeostasis
  • The graded potential only lasts about 10 milliseconds then the RMP is restored
29
Q

Can graded potentials be summed?

A

Yes, they can be summed

30
Q

Can graded potentials be depolarized or hyperpolarized or both?

A

Both, it can be either depolarized (decrease (-)) or hyperpolarized (increase (-))

31
Q

How are graded potentials brought back to homeostasis?

A

There is a negative mechanism that brings them back to the RMP

32
Q

What kinds of changes do graded potentials make (in terms of area)?

A

Local changes

  • Small areas
  • The voltage changed caused by a graded potential does not spread more than a few micrometers along the cell membrane
33
Q

Are hyperpolarizing graded potentials more (+) or (-) charged?

A

More (-) charged

  • On a graph, it goes down (below the RMP)
34
Q

Are hyperpolarizing graded potentials less (+) or (-) charged?

A

Less (-) charged

  • On a graph, it goes up (above the RMP)
35
Q

How can graded potentials be summed?

A
  1. If they are near to each other
  2. If they are close enough together in time
36
Q

What is it called when graded potentials are summed when they’re near to each other?

A

Spatial summation

Spatial - S - Think of “space”

37
Q

What is it called when graded potentials are summed when they’re enough together in time?

A

Temporal summation

Temporal - T - Think of “time”

38
Q

Where can AP occur?

A

AP can occur in any cell with an excitable membrane

  • Includes muscles, neurons (axons of neurons)
39
Q

What does AP cause in terms of voltage?

A

The AP causes a brief reversal of the voltage

40
Q

Can APs be summed?

A

No, the AP is never summed

41
Q

Can AP happen partially?

A

No, the AP is an all-or-none phenomenon

42
Q

What mechanism does AP work by?

A

A positive feedback mechanism

43
Q

What are the phases of AP & ion channels??

A

Resting phase
- all channels are closed

Depolarizing phase
- Na+ ATPase opens
- Stimulus causing voltage to rise (e.g., ligand-gated Na+ channels opening)
- Voltage-gated Na+ channels opening

Repolarizing phase
- K+ ATPase opening & Na+ ATPase closing
- Voltage-gated K+ channels opening and Na+ channels closing

Hyperpolarizing phase
- K+ ATPase open & Na+ ATPase closed
- Voltage-gated K+ channels still open and Na+ channels closed

Resting phase
- all channels are closed

44
Q

What phase(s) of the AP and the ion channels are positive feedback?

A

The depolarizing phase

45
Q

What phase(s) of the AP and the ion channels are negative feedback?

A

Repolarizing phase & hyperpolarizing phase

46
Q

What are the 2 types of refractory periods?

A

Absolute refractory period & relative refractory period

47
Q

What are refractory periods?

A

Cell cannot fire again
- Need space between AP to have accurate signals

48
Q

How does absolute refractory and relative refractory differ?

A

Absolute refractory period:
- No AP possible
- The inability to send a new impulse
- Because the sodium channels are inactivated

Relative refractory period:
- APs are harder to start
- Need more APs to send a new impulse
- This is the interval immediately after the absolute refractory period
- It is possible to send a new impulse but needs greater stimulus

49
Q

Do APs only come from internal?

A

APs can come from both external & internal as long as there’s a voltage change

50
Q

What measures the electrical activity in the muscles?

A

Electromyography (EMG)

51
Q

How does electromyography (EMG) work?

A

Measures the movement of ions around the body and how conductive you become when all these different channels are moving back & forth

52
Q

What are controlled by nerves that react to electrical stimulation?

A

Muscles

53
Q

How to generate AP in nerves?

A
  • Bring up to the voltage threshold (can be done with external current)
54
Q

How to contact a muscle?

A

Stimulation
- Just need to bring a voltage to the nerve to generate APs which will cause muscle contractions
- Message send through the nerve to the muscle (as AP)
- Muscle contacts when voltage brought to the threshold

55
Q

What does the time from the stimulation to the contraction of the muscle tell you?

A

It tells you how quickly that nerve conducts

56
Q

Why can’t we let go of a 60Hz AC current?

A

B/c the alternating current is 60Hz (60 cycles/sec) and our neuron fires approximately 60 times/sec which is the same frequency thus we can’t let go

57
Q

What is a synapse?

A

The tiny gap between the axon of a neuron and the muscle

1H06A (8 decks)

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