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Cell Biology > Membrane Potential ✅ > Flashcards

Membrane Potential ✅ Flashcards

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1
Q

What are the different types of membrane potentials?

A
  • resting potential
  • action potential
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2
Q

What is the “resting membrane potential”?

A

The electrical charge of cells that can be measured across their outer cell membrane.

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3
Q

Why is the electrical membrane potential in nerve and muscle cells unique?

A

The electrical membrane potential can be changed as the result of synaptic signalling from neighbouring cells.

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4
Q

What is an action potential? When does it occur?

A

When the membrane potential of a nerve or muscle is reduced sufficiently (-55mV) (from -70mV), a further dramatic change occurs in the membrane potential (+30mV).

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5
Q

Explain briefly how the resting electrical membrane potential achieved.

A
  • the result of the differential separation of charged ions, especially Na+ and K+ across the membrane
  • the result of the differential permeability of the membrane to these ions diffusing back down their concentration gradient.
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6
Q

What is the resting membrane potential?
What is its value and units?

A

A resting potential is the DIFFERENCE in CHARGE across the membrane when a neuron is NOT FIRING.

In a typical resting potential, the inside of the neuron is more negative relative to the outside (approximately –70 mV).

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7
Q

Explain in detail how the resting electrical membrane potential achieved.

A
  • sodium-potassium pump: a transmembrane protein that actively exchanges sodium and potassium ions.
  • expels 3 Na+ ions
  • admits 2 K+ ions
  • ATP hydrolysis required
  • energy-dependent process

–> An electrochemical gradient is created: the cell interior is negative compared to the extracellular environment
(as there are more positively charged ions outside of the cell and more negatively charged ions inside the cell)

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8
Q

What are the three major factors that cause the resting membrane potential?

A

1) Differential permeability of the membrane to the diffusion of ions.
(The membrane is more permeable to K+ ions than Na+ ions)
2) Negatively charged anions trapped in the cell
(Intercellular anions (macromolecules) are too large to get out through the cell’s plasma membrane).
3) The sodium-potassium (Na+ -K+) pump

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9
Q

Which ions is the membrane more permeable to?

A

membrane is more permeable to K+ ions that Na+ ions)

K+»>Na+

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10
Q

What happens to negatively charged anions inside the cell?

A

They get trapped as intercellular anions (macromolecules) are too large to get out through the cell’s plasma membrane.

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11
Q

How is ATP derived?

A
  • Through cellular respiration
  • It requires glucose and oxygen
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11
Q

What are the 6 major parts of the transmission of electrical signals?

A

1) Stimulus (must exceed the threshold potential (-55mV))
2) Depolarization (Na+ in, sodium channels open)
3) Action potential (+30mV)
4) Repolarization (K+ out, potassium channels open)
5) Hyperpolarization (-80mV) (sodium-potassium pump is activated)
6) Resting state (Na+-K+ pump reestablishes +70mv)

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12
Q

What controls the movement of ions across the membrane of a neuron?

A

Ion channels control the movement of ions across the neuronal membrane.

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13
Q

What are four properties of ion channels?

A
  • selective,
  • passive or active,
  • regionally located,
  • functionally unique.
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14
Q

What are ion channels made of?

A

Integral proteins (that cross the membrane).

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15
Q

What three factors determine the selectivity of an ion channel?

A
  • The charge of the ion (positive or negative)
  • The size of the ion
  • How much water it attracts and holds around it.
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16
Q

What’s the difference between an active and passive ion channel?

A

Active channels have gates that can open or close the channel,

Passive channels (leakage channels) are always open. Ions pass through them continuously.

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17
Q

Is a resting neuronal cell membrane more positive inside or outside?

A

It is more positive on the outside.

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18
Q

What is the result of the charge separation in a resting neuronal membrane?

A

The difference in ions produces a voltage across the cell membrane. This voltage is called the membrane potential.

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19
Q

When the neuronal membrane is at rest are the voltage-gated channels opened or closed?

A

When the neuronal membrane is at rest, the voltage-gated channels are closed.

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20
Q

What happens to the voltage-gated channels when there is a nerve impulse (or action potential) in the neuronal membrane?

A

During a nerve impulse (an action potential), the voltage across the membrane changes, causing voltage gated channels to open and close.

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21
Q

Why, when the Na+ voltage-gated channel opens, does the membrane potential goes from -70 mV to less negative values.

A

When the Na+ voltage-gated channels open, Na+ flows into the cell, causing an increase in membrane potential (Na+ is positively charged).

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22
Q

Why, when the K+ voltage-gated channel opens, does the membrane potential goes from +30 mV to more negative values (-80mV).

A

When the K+ voltage-gated channels open, K+ flows out of the cell, causing a decrease in membrane potential as K+ is positively charged, and it is leaving the cell.

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23
Q

Give two general types of active channels.

A

Na+ voltage-gated channel and K+ voltage-gated channel.

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24
Q

What will open a chemically-gated ion channel in a neuron?

A

A neurotransmitter, such as acetylcholine and GABA.

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25
Q

When a neurotransmitter opens a chemically-gated channel, does the neurotransmitter go into the cell?

A

No, the neurotransmitter stays in the synapse.

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26
Q

When acetyl choline binds to its receptor, which ion(s) will move across the membrane? In which direction will they move?

A

Sodium ions (Na+) will move into the cell, while potassium ions (K+) will move out of the cell.

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27
Q

When GABA binds to its receptor, which ion(s) will move across the membrane? In which direction will they move?

A

Cl- ions will move into the cell.

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28
Q

What determines the direction that ions move through an ion channel?

A

The chemical gradient and the electrical force.

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29
Q

On what parts of the neuron do we find passive channels?

A

Passive channels are located in the cell membrane on the dendrites, the cell body, and the axon.

30
Q

On what parts of the neuron do we find chemically-gated channels?

A

Chemically-gated channels are mainly located on the dendrites and the cell body.

31
Q

On what parts of the neuron do we find voltage-gated channels?

A

Voltage-gated channels are mainly found on the axon hillock, along the unmyelinated axons, and at the nodes of Ranvier in myelinated axons.

32
Q

Which of Na+, K+, Cl- ions have a high concentration outside the cell and which have a high concentration inside the cell?

A

High concentration inside the cell: K+ (balanced by a high concentration of negatively charged proteins and other anions)
High concentration outside the cell: Na+, Cl-

33
Q

What is the only way that ions can get across the cell membrane?

A

Ions (insoluble in the lipid bilayer) can only cross through ion channels (watery pores).

34
Q

Which ion are most cells in the body permeable to?

A

Potassium (K+)

35
Q

What’s the difference between a neuron’s permeability to sodium and potassium?

A

Excitable cells are very permeable to K+ and slightly permeable to Na+.

36
Q

What two factors will affect the permeability of a cell for a particular ion?

A
  • Number of channels for the ion,
  • The ease with which the ion can move through the channels.
37
Q

What mechanism is used by the nervous system to produce rapid changes in membrane permeability?

A

The permeability of a cell for a given ion increases when gated channels for that ion are opened.

38
Q

As opposed to neurons, simple, non-excitable cells are permeable only to one ion. What is that ion?

A

Potassium (K+).

39
Q

What major factor causes ions to move through ion channels?

A

Gradients cause ions to move (eg. K+ diffuses down its concentration gradient).

40
Q

What type of force is the concentration gradient?

A

A chemical force.

41
Q

How does the cell membrane become more positive outside and more negative inside?

A

As K+ ions diffuse out of the cell, they accumulate on the outside surface of the cell membrane, making it more positive than the inside surface of the cell membrane. This results in a separation of charge across the cell membrane.

42
Q

What type of force is created by the separation of charge?

A

The separation of charge creates an electrical potential or voltage across the cell membrane.

43
Q

As potassium diffuses out of a cell, the outside of the cell becomes more ….. and the inside of the cell becomes more ….. Since opposite charges attract each other, and potassium is positive, the potassium will be …….

A

positive
negative
pulled back into the cell.

44
Q

What is an electrical potential?

A

The force that is responsible for the movement of positive potassium ions back into the cell, where it is more negative is called the electrical potential.

45
Q

What effect do both the chemical force and the electrical force have on K+?

A

K+ will continue to diffuse out until the electrical potential is equal but opposite to the force from the concentration gradient.

46
Q

What is a membrane potential?

A

The electrical potential across the cell membrane.

47
Q

In what units is both the concentration and the membrane potential measured?

A

It is measured in millivolts (mV).

48
Q

What is a typical value for the resting membrane potential?

A

-70mV

49
Q

Does the sodium-potassium pump move sodium and potassium with or against their gradients?

A

Against their concentration gradients.

50
Q

What provides the energy to pump sodium and potassium against their gradients?

A

The pump uses ATP.

51
Q

What is another name for an action potential?

A

Nerve impulse

52
Q

Where is the action potential generated?

A

The action potential is generated at the axon hillock.

53
Q

What causes an axon potential to occur at the axon hillock?

A

At the axon hillock, the density of voltage-gated Na+ channels is greatest.

54
Q

What happens to ion channels when the membrane depolarizes at the axon hillock?

A

Voltage-gated channels for Na+ open rapidly, increasing membrane permeability to Na+.

55
Q

How much does the axon hillock have to depolarize to reach the threshold?

A

15mV (until -55mV)

56
Q

What happens at the threshold?

A

At the threshold an action potential is generated.

57
Q

What happens if there is a weak stimulus at the axon hillock and the threshold is not reached?

A

Weak stimuli that do not reach the threshold do not produce an action potential. (It is an all-or-none-event).

58
Q

Do action potentials always have the same amplitude and the same duration?

A

Action potentials always have the same amplitude and the same duration

59
Q

What happens to sodium voltage-gated channels at the threshold?

A

At the threshold, depolarization opens more voltage-gated Na+ channels.

60
Q

Explain how the positive feedback loop maintains the rising phase of the action potential.

A

At threshold, depolarization opens more voltage-gated Na+ channels. This causes ore Na+ to flow into the cell, which in turn, causes the cell to depolarize further and open even more voltage-gated sodium channels. Loop: Depolarization —> open voltage-gated Na+ channels —> Inward flow of Na+ —>

61
Q

The rising phase of the action potential ends when the positive feedback loop is interrupted. What two processes break the loop?

A

The inactivation of the voltage-gated sodium channels (Na+ channels).

The opening of the voltage-gated potassium channels (K+ channels).

62
Q

What are the names of the two gates on the voltage-gated sodium channels?

A
  • Voltage-sensitive gate (opens as the cell is depolarised)
  • time-sensitive inactivation gate (stops the movement of Na+ through the channel after the channel has been open for some time.)
63
Q

What happens to the voltage gated sodium channels at the peak of the action potential?

A

At the peak of the action potential, voltage-gated Na+ channels begin to inactivate. As they inactivate the inward flow of Na+ decreases, and the positive feedback loop is interrupted.

64
Q

When do the voltage-gated potassium channels open?

A

They begin to open slowly only when the action potential reaches its peak.

65
Q

What happens when the voltage-gated potassium channels open and the potassium moves out of the cell?

A

As K+ moves out, depolarization ends, and the positive feedback loop is broken.

66
Q

When does repolarization occur?

A

With less Na+ moving into the cell, and more K+ moving out, the membrane potential becomes more negative, moving toward its resting value.

67
Q

What is hyperpolarization?

A

The slow voltage-gated K+ channels remain open after the cell has repolarized. K+ continues to move out of the cell, causing the membrane potential to become more negative than the resting membrane potential.

68
Q

What is the absolute refractory period?

A

After the neuron has generated an action potential, it cannot generate another one. Many Na+ channels are inactive and will not open. Most K+ channels are open.

69
Q

Why can’t a neuron generate another action potential during the absolute refractory period?

A

Because:
- sodium ions. (Na+) cannot move in through inactive channels,
- potassium ions (K+) continue to move out through open voltage-gated channels.

70
Q

What is the relative refractory period?

A

Immediately after the absolute refractory period, the cell can generate an action potential, but only if it is depolarized to a value more positive than normal threshold. (This is because some Na+ channels are still inactive while some K+ channels are still open.)

71
Q

What is conduction velocity?

A

The speed at which an action potential is propagated.

72
Q

What two factors does conduction velocity depend on?

A
  • the diameter of the axon
  • how well the axon is insulated with myelin
73
Q

What is the effect of myelin on conduction velocity?

A

name: Saltatory conduction.

  • myelinated axons have areas of insulation interrupted by areas of bare axon (node of Ranvier)
  • in a myelinated axon, charge flows across the membrane only at the nodes, and therefore an action potential is generated only at the nodes.
  • action potential jumps along the axons.

Cell Biology (12 decks)

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