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BRS - Bioregulatory Systems Week 1 > Membrane Potential and Action Potential > Flashcards

Membrane Potential and Action Potential Flashcards

1
Q

What is diffusion and flux and where is this method of transmission efficient / useful?

A

Movement of molecules down a concentration gradient until an equilibrium is achieved

Over short distances and when no energy input required

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2
Q

What is a flux of ions?

A

The number of molecules that cross a unit area per unit of time e.g. molecules.m^-2.s^-1

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3
Q

What are the properties of ions?

A

Like charged ions repel

Oppositely charged ions attract

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4
Q

What is voltage VS current VS Resistance?

A

Voltage - Same as potential difference. measured in Volts, generated by ions to produce a charge gradient

Current - measured / describes in Amps, it is the movement of ions due to the potential difference

Resistance - measured in Ohms, barrier that prevents movement of ions

In the picture: Volts doing the pushing of the current (Amps) against the resistance (Ohms)

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5
Q

Do all cells have membrane potentials (MPs)?

How can you measure membrane potential and what is the resting membrane potential of a typical nerve cell?

A

Yes

By placing one electrode inside the cell and the other in saline solution of zero-volts outside of the cell. The electrodes are both connected to a voltmetre, which shows the p.d. and so the MP

-70 mV

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6
Q

How do cells get across ions across their membranes (a hydrophobic layer) and what are their features?

A

Ion channels / pumps - they give the membrane permeability to the ions

Ions channels can be selective i.e. selective to the type of ion Ca2+ or Na+ etc.

Movement occurs when the channel is open

Can open and close in response to ligands / various MPs

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7
Q

How is the MP produced?

If the membrane is impermeable, how is MP affected?

A

Due to the diffusion of ions across a selectively permeable membrane

If there is no way for ions to get across, difference in ions inside and outside makes no difference to the MP, as the MP always equals 0

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8
Q

Explain what will happen in this picture? (Compartment 1 has Na+ ions, compartment 2 has K+ ions, and there are K+ channels that allow for the diffusion of K+)

What is the electrochemical equilibrium?

A

When K+ channels are introduced, K+ diffuses into compartment 1 down the concentration gradient, making compartment 1 more positively charged and compartment 2 more negatively charged

Eventually the difference in charges prevents the net movement of K+ ions into compartment 1 to stop

So an electrochemical equilibrium is reached - electrical forces exactly balance the diffusion forces

This forms a stable (trans)membrane potential (MP)

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9
Q

What is the equilibrium potential?

A

The potential at which the electrochemical equilibrium is reached - so the potential that prevents the diffusion of ions down the concentration gradient (no net movement of ions)

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10
Q

What is the Nerst equation and what is it used to calculate?

A

Equilibrium potential (E) - states E in mV

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11
Q

How can the Nerst equation be simplified?

This is a picture of a simplified Nerst Equation calculated:

A

By assuming T = 37 degrees C (like in our bodies) = 310 Kelvins

Convert natural log to log base 10

Typical concentrations of the ion inside and outside of the cell

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12
Q

What is the composition of the main fluid compartments in the intra and extra cellular fluids?

A

[At least learn the highlighted ones]

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13
Q

Using these typical intracellular and extracellular concentrations, calculate the theoretical E values (in mV)?

A

The theoretical E values for K+ and Na+ come out to be:

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14
Q

What is the typical value of E and why do membrane potentials not rest at the equilibrium of Na+ or K+?

A

The membrane is not fully specific in the ion it transports at any one time, so there is still some leakage of ions across the membrane

At rest, although K+ channels are the only channels fully open, there is still a small entry of Na+, so the E value instead rests at -70mV (rather than -90mV)

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15
Q

What is GHK equation and why is it better?

A

Takes into account the the relative permeability of each ion

More physiologically relevant

More specific / accurate / exact

P is the relative permeability of each ion, so when P=1 channel is open, P = 0.5 channel is open half the time, P=0 channel is closed

Takes into account the small permeability during RMP - e.g. Na+ channels only open for like 5% of the time

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16
Q

What do both these equations show during depolarisation?

A

The inside of the cell becomes more and more positive as the Na+ channels open, so the membrane potential increase

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17
Q

Some worked examples using the GHK equation to show how the membrane at resting potential is slightly permeable to Na+, despite supposedly being only permeable to K+, changes the RMP from -90mV to around -70mV?

A

.

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18
Q

What is depolarisation?

A

MP increases from negative and goes towards 0mV

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19
Q

What is repolarisation?

A

MP decreases (becomes more negative) towards the RMP

20
Q

What is overshoot?

A

MP increases (becomes more positive) above 0mV

21
Q

What is hyperpolarisation?

A

MP decreases (becomes more negative) beyond the RMP

22
Q

A diagram to explain / label the terms depolarisation, repolarisation, overshoot and hyperpolarisation?

A

.

23
Q

What are graded potentials?

A

Change in MP in response to stimuli e.g. light

They are dependent on the nature and size of the stimulus, and decay along the axon

24
Q

What can different stimuli lead to in MPs, and what specific property causes these differences?

A

Some stimuli lead to hyperpolarisation, some lead to depolarisation

Some stimuli are stronger, and some stimuli are weaker and so lead to a larger ro smaller change in MP

Depending on whether the threshold value is reached, an AP is generated

These differences in MP are in response to different stimuli and are due to different ion permeabilities being activated according to the NT being released in the synapses between receptors, nerves etc.

25
Q

Why do small stimuli that cause a small depolarisation in MP fade away along the axon, over a distance?

A

Because as the deploarisation travels along the axon, some of the charges ‘leak’ out of the axon, til the charge in the membrane is insufficient to cause an AP

26
Q

What are graded potentials dependent on?

A

Length of axon

Size of stimulation

Nature of the stimulation

27
Q

Where are graded potentials likely to occur?

A

Sensory receptors

Synapses

28
Q

What can graded potentials do / why are they useful?

A

Can contribute to or prevent APs being formed

Filter out background stimuli

29
Q

What are action potentials (APs) and where do they occur?

A

Known as nerve impulses in neurons - allow for excitation to be carried down an axon

Allow transmission over long distances e.g. all they way to the effectors

Occur in all excitable cells - neurons, muscle cells and some endocrine tissue

30
Q

What is the diff between GPs and APs

A

idk

31
Q

Why are APs important / useful?

A

Reliable and quick in neurons

32
Q

How do action potentials work on an ionic basis? i.e. What does permeability of the ions depend on?

A

Conformational state of the ion channels

Opened by depolarisation e.g. Na+ channels open

Inactivated by sustained depolarisation - electrochemical gradient reached

Closed by repolarisation / hyperpolarisation

33
Q

What 2 things happen when the membrane permeability of the ion increase?

A

The ion moved down the electrochemical gradient

MP moves towards equilibrium potential (E) of the ion

34
Q

Why are Na/K pumps important?

A

Allow for the concentration gradient of the ions to be maintained - i.e. during RMP

Which is the basis or nerve impulses, as the opening of different ion channels can then activate an AP

However, pumps do not contribute directly to the AP (i.e. do not cause depolarisation, repolarisation etc.)

35
Q

What is meant by an ‘all or none’ event?

A

Either it happens or it doesn’t- If the threshold value is reached, an AP is generated

36
Q

What are the 5 phases of an AP?

A

RMP

Depolarisation

Upstroke / Overshoot

Repolarisation

Hyperpolarisation

All happen rapidly between 2-3 ms

37
Q

Describe the different phases of the AP?

A

RMP - maintained as the membrane is more permeable to K+ than Na+, MP lies close to E of K+ than Na+ at -70mV

Depolarisation - receptor activated by a stimulus, which moves the MP towards 0 (positive direction) to the threshold value

Upstroke - threshold value reached, voltage gated Na+ channels open quickly at this mV, voltage gated K+ channels also open at this mV but more slowly so fewer K+ diffuse in, MP moves towards E of Na+

Repolarisation - Na+ channels are inactivated, Na+ stops diffusing into the cell, K+ channels are now fully open so K+ diffuses out of the cell down the electrochemical gradient, MP moves towards the E of K+

Hyperpolarisation - VG K+ channels remain open so K+ continues to leave down the electrochemical gradient. the VG channels close when the MP is close to the E of K+, eventually the MP returns to the RMP, resting potential K+ pumps stay open

38
Q

How are the Na+ channels inactivated, what does it cause and why is it important?

A

The channel is a large protein that has 2 mechanisms at the threshold value, first it opens up to allow for the flow of Na+

After, a part of its protein structure blocks the channel to stop the flow of Na+

This causes a refractory period

New stimulus cannot be evoked as the Na+ channels are taken out of action, and the plug is removed during repolarisation

39
Q

What is active propagation?

A

How the AP is conveyed down the axon

After an AP, Na+ diffuses along the axon, increasing the next part of the axon’s MP to reach the threshold value, triggering another AP, and so on

40
Q

Where are VG channels located?

A

At the nodes of Ranvier

41
Q

What are nodes of Ranvier and what is saltatory conduction?

A

Myelinated axons have gaps called nodes of Ranvier

APs are formed at these nodes, and in the myelinated (insulated) areas, the ions diffuse across so the next AP can be generated at the next node

42
Q

What affects conduction velocity?

A

Diameter / axon size (conduction velocity is proportional to the square root of the axon diametre)

Myelinated or not (insulation)

43
Q

What are some examples of diseases that reduce myelination of axons and how does this affect the person?

A

Multiple sclerosis and diptheria

Reduces the speed at which signals can be transmitted

44
Q

What are the 3 main factors that influence the movement of ions across the membrane?

A

Charge 1+/- or 2+/-

The concentration of the ion on both sides of the membrane

Voltage across the membrane - influences drive across the membrane

45
Q

Why is the K+ equilibirum potential (E) negative at -90mV, but the Na+ E positive at +72mV, when both these ions are positive?

A

Due to the relative concentrations of Na+ and K+ inside and outside the cell

There is a higher [K+] inside than outside the cell, so K+ diffuses out creating a negative E

Opposite for Na+. there is a higher [Na+] outside than inside the cell, so Na+ diffuses in creating a positive E

A negative E for K+ is required to attract the K+ to stop net outwards flow, a positive E for Na+ is required to repel the Na+ to stop Na+ from entering the cell

46
Q

Which ion is important for the upstroke of and which for the repolarisation, and in which direction do these ions move?

A

Upstroke - Na+ moving down their concentration gradient into the cell

Repolarisation - K+ ions going down their concentration gradient out of the cell

47
Q

What factors influence the speed of propagation of an AP along an axon?

A

Larger axons have a lower resistance, so ions move faster (conduction velocity is proportional to the square root of the axon diametre)

Linear relationship between conduction velocity and myelin thickness

BRS - Bioregulatory Systems Week 1 (13 decks)

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