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Cell Biology > Membrane Potentials > Flashcards

Membrane Potentials Flashcards

1
Q

What is resting memebrane potential

A

Electrical potential difference across the membrane. Usually -70 mv

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2
Q

What is an action potential and where does it stem from

A

A rapid change in membrane potential. The permeability or k+ and Na changes

Forms in the axon hillock

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3
Q

Which channel maintains the negative rmp directly

A

The k+ leak channel. K+ moves out of cell via diffusion down conc gradient

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4
Q

Why is the membrane called impermeable to NA+ and permeable to K+

A

Because when cell is resting k moves out of cell freely via the k leak channel

Na+ in transported back out of the cell by the Na pump (ATPase) actively when na tries to move in by diffusion (leak channel)

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5
Q

What 2 things cause chemical disequilibrium

A

The high permeability to k+ and the active transport of na + out of cell when resting

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6
Q

Why is the na+ pump called electro genic

A

Because it changes the potential difference of the outside to be more positive

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7
Q

What does the electrical gradient mean when talking about the k leak channel

A

The more k diffuse out of cell the bigger the electrical charge difference (electrical gradient)

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8
Q

What happens eventually when so many k+ leave the cell

A

They become attracted back into the cell due to the big negative charge

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9
Q

Why do k+ eventually stop moving via leak channel

A

When the electrical gradient becomes equal and opposite to the concentration gradient = k has no net movement

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10
Q

What is another word for when the k+ stop moving from leak channel

A

The equilibrium potential (Ek)

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11
Q

Which equation is used to calculate the equilibrium potential

A

Nernst equation finds the voltage of it

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12
Q

What is the voltage of Eion in Na and K

A

K = no net movement at -86mv

Na = + 60 mv (due to it moving in cell)

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13
Q

What generates the resting membrane potential

A

The equilibrium potential of the ions average out at -70mv - closest to the Ek because resting cell is permeable to K

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14
Q

Which 2 channels are involved in action potentials

A

Voltage gated K+ channel

Voltage gated na+ channel

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15
Q

Explain what happens when a cell is activated and it goes into slow depolarisation

A

Some Na+ channels open and they move in cell by diffusion

If they reach threshold of -55mv rapid depolarisation occurs

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16
Q

When threshold is met what happens in rapid depolarisation

A

All voltage gated Channels open and Na+ rush into cell through the ACTIVATION GATE

This occurs till a potential or +40/60 mv is met

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17
Q

Why does depolarisation eventually slow down and stop

A

K+ channels some open and k+ starts to leave the cell which opposes the positive charge of cell

18
Q

What occurs in repolarisation

A

The inactivation gates on the Na+ voltage gated channels close. No more Na move in

The k+ voltage gated channels become active and k+ leaves the cell slowly bringing the charge of cell down

19
Q

Why does hyperpolarisation occur after repolarisation

A

K+ channels are slow to shut and more k+ keep leaving the cell which means cell becomes too negative

However they do finally close

20
Q

What happens after hyperpolarisation

A

The resting state is tried to be reinstated by the k+ leaky channels and the Na+ pump

21
Q

When do activated gates actually close in voltage gated channels

A

They stay open all the way through Ap until the resting state is met again

22
Q

What is the absolute refractory period

A

Membrane cannot generate another AP no matter the stimulus size

Na+ channels are inactivated

23
Q

What is relative refractory period and when does it occur

A

Period when there can be another ap generated but stimulus needs to be bigger
Some Na channels recovered
Some k+ stay open

Happens in hyperpolarisation. This means the stimulus has to be stronger due to very negative charge

24
Q

How does Ap move across the axon

A

In current loops

When the neighbouring Na+ channels open the previous ones go into repolarisation stage and the next is depolarised

25
Q

Why is the refractory period important

A

To keep AP unidirectional

26
Q

What is the velocity of the Ap related to

A

Diameter and memebrane resistance

Bigger and higher resistance = faster ap

27
Q

How does a bigger diameter allow for faster ap

A

More room for current flow (eg depolarisation)

28
Q

Why does a bigger membrane resistance (Rm) cause a faster AP

A

Less current lost by leakage out of cell

29
Q

How is membrane potential increased

A

The myelin sheath because it insulates it

30
Q

How do ap move down axon - if not through myelin sheath

A

They jump via nodes of ranvier (saltatory conduction)

31
Q

What would happen if the axon was myelinated

A

Can cause diseases such as MS due to action potentials stopping (no saltatory conduction)

32
Q

Explain the structure of the post synaptic membrane in a neuromuscular junction

A

There are junctional folds on the membrane which have the Ligand gated Na channels

The membrane is called the muscle end plate

33
Q

Explain the steps of transmission in a neuromuscular junction

A

When an ap gets to axon terminal it depolarises the pre synaptic membrane

Depolarisation causes the voltage gated calcium channels to open and calcium diffuses into cell

Ca causes vesicles to fuse with membrane and exocytosis of acH occurs

AcH then binds to receptors on the ligand gated Na channels and opens them

Sodium diffuses into the post synaptic neurone

K+ moves out of the post synaptic neurone using the same channel (anti Porter)

34
Q

What is the end plate potential

A

The membrane potential when Na moves in and K moves out

35
Q

What is the equation for the EPP end plate potential

A

Ena + Ek / 2

EPP is half way between equilibrium potentials for the ions

36
Q

What is the voltage of the EPP

A

-15mv

37
Q

Why is there no action potential that occurs at the NMJ

A

There are no Na voltage gated channels

Epps instead trigger ap nearby in muscle to trigger contraction

38
Q

What is a mini EPP

A

Slight change in voltage when cell is at rest of the NMJ. This is the fusion of an acH vesicle on presynapse (0.5 mv)

39
Q

What is the safety factor for EPP

A

200-300 vesicles fuse even though only 100 are needed to open channels

40
Q

What happens to acH when it unbinds from the ligand gated channels

A

Acetylcholine esterase (acH ase) breaks it down into acetate and choline

Choline is then reacted with acetyl co A to reform AcH into the vesicles

41
Q

What gates in Na voltage channels are closed and open in the relative refractory period

A

The inactivation gates are open - go back to resting state and the activation gates are closed but can reopen with a big stimulus

42
Q

What does electrogenic mean

A

Changing the potential difference

Cell Biology (21 decks)

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