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Neurosciences > Membrane & Action potentials > Flashcards

Membrane & Action potentials Flashcards

1
Q

Where do electrical signals start?

A

They start in the receptor cells

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2
Q

What three kinds of electrical potentials are there?

A
  1. Receptor Potential
  2. Synaptic potential
  3. Action potential
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3
Q

Which of the three types of electrical potential is the fastest?

A

Action potential is the fastest

Synaptic is the second and the third is Receptor potential

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4
Q

What are the requirements for electrical signaling between nerve cells?

A
  1. Must be fast
  2. Must cross a long distance
  3. Should not lose strength
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5
Q

What is the nature of the resting potential inside a cell, compared to the extracellular environment?

A

The nature of the charge is negative ( -65 mV )

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6
Q

What happens when you feed a positive current into a nerve cell? What happens if you increase the strength?

A

The positive current will depolarize the cell until the threshold is met. This translates to an action potential. A stronger positive current does not result in a stronger action potential but leads to multiple action potentials.

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7
Q

What would happen if only passive conduction was present?

A

The charges would diffuse across the cell - the signal becomes weaker the further it goes.

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8
Q

What is the benefit of active conduction compared to passive conduction?

A

The signal does not lose strength over time.

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9
Q

What two principles is the resting membrane potential based on?

A
  1. Diffusion of particles (from high concentration to low concentration)
  2. Electrical forces between electrical charges (positive and negative forces)
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10
Q

What are the four main ions for signal transduction in neurons?

A

K+ , Na+ , Cl- and Ca2+

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11
Q

What happens at the electrochemical equilibrium?

A

At the equilibrium, the diffusion forces will equal the electrical forces of the ions (K+)
No net movement of K+ ions on either side of the membrane.

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12
Q

What is the equilibrium potential?

A

The potential at the electrochemical equilibrium.

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13
Q

Why don’t ion concentrations change, if there are ions flowing in an out constantly, even at a resting membrane potential?

A

Because the amount of ions creating this flow is very small. About one millionth of the total concentration.
(Small, almost non-detectable shift)

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14
Q

What can you use the Nernst equation for?

A

Calculating the Equilibrium potential.

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15
Q

What is the reversal potential?

A

The reversal potential creates a flow that brings the potential back to the equilibrium if the concentrations deviate.

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16
Q

What is hyperpolarization and depolarization, regarding the resting potential?

A

Hyperpolarization goes under the resting potential (becomes more negative) and depolarization goes above the resting potential (becomes more positive)

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17
Q

What factors influence the resting potential?

A

Concentrations of K+, Na+ and Cl- inside and outside the cell, as well as the membrane permeability for those ions (Ca2+ is NOT found freely inside or outside the cell)

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18
Q

What ion channels are leaky on the membrane?

A

K+ ion channels are leaky.

Na+ channels are closed

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19
Q

What ion dominates the resting membrane potential mechanism?

A

K+ dominates the control of the resting membrane potential.

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20
Q

What happens if the extracellular concentration of K+ is increased?

A

The resting membrane potential is also increased (becomes more positive)

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21
Q

Why does K+ dominate the resting membrane potential?

A

Because the permeability for K+ is much higher than all other ions, at the resting membrane potential.

22
Q

What happens to permeability during an action potential?

A

The membrane becomes much more permeable for Na+ ions than K+ ions, thus creating an ion flow.

23
Q

What is the function of ion transporters?

A

It does active transport of ions against the gradient. This costs energy (ATP)

24
Q

What is the function of ion channels?

A

It allows ions to diffuse down the concentration gradient. Those are selectively permeable for certain ions.

25
Q

Roughly explain how the Na/K ATPase pump works

A

The enzyme starts with a high affinity for Na+. After 3 Na+ ions bind to the enzyme, ATP phosphorylates the enzyme, which changes configuration and opens the gates on the other side. The affinity changes and the Na+ is released. The enzyme then gets a high affinity for K+. After the K+ bings to the enzyme, it dephosphorylates and changes configuration again, releasing K+ on the other side and gaining a high affinity for Na+ again. (a transport cycle)

26
Q

How much approximate energy does the Na/K ATPase use in the brain?

A

Around 20 - 40% of the energy consumption in the brain.

27
Q

Why is the efflux of Na+ reduced when external K+ is removed?

A

Because relatively less K+ will bind to the Na/K ATPase

28
Q

What happens when the ATPase activity is blocked?

A

The efflux of Na+ is greatly reduced, as the protein cannot get phosphorylated.

29
Q

What is the energy source of Ion exchangers?

A

The ion gradient op the ions it transports.

30
Q

What ion is (usually) used for Co-transport and anti-port

A

Na+ is usually used as an “exchange” for other ions.

31
Q

What are the model requirements for studying electrical signaling in nerve cells?

A
  1. Nerve cells that produce action potentials

2. It is well accessible

32
Q

Why were the first nerve experiments done on squids?

A

The squid had a giant axon which was easily accessible.

33
Q

What two types of recordings were performed on the squid experiment in the 50s?

A
  1. Voltage clamp - Artificial changes in voltage, induced with current
  2. Current clamp - induce a current to see how the voltage changes over time
Voltage = amount of mV
Current = flow of ions
34
Q

What is the difference in duration of how long ion channels are open, for Na+ and K+ channels?

A

K+ channels are open for a longer amount of time than Na+ channels.

35
Q

Why do Na+ channels remain closed after a brief moment of depolarisation?

A

The Na+ channels are affected by two mechanisms. The first mechanism is the opening of the channel after depolarisation. After it has been activated, a second mechanism is put in motion, that blocks ions from passing through. It is like a cork on a wine bottle.
The Na+ ion channel is open, but inactive and cannot transport Na+ inwards for a brief moment of time, until the “cork” is removed.

36
Q

What are the two components of the Na+ ion channel? (two mechanisms)

A
  1. Fast activation gates - open during depolarisation

2. Slow inactivation gates - close during depolarisation

37
Q

Why is it important that the inactivation gates in the Na+ ion channel are slower than the fast activation gates?

A

Because otherwise current will be completely impaired and no flow would happen. With this system, the flow is controlled, as only a small discharge is needed.

38
Q

What is the refractory period?

A

The period after an action potential, in which no other action potential can happen again

39
Q

Why is there a refractory period?

A

This has to do with the inactivation of the Na+ channels. After the opening of the channels, the slow inactivation gates cover up the channel and don’t let ions through. They keep it covered for some time - during which no flow is possible, even after another depolarisation.

40
Q

What leads to the opening of K+ channels?

A

A change in the voltage

K+ channels have a (depolarized) voltage sensor

41
Q

What types of ion channel classes are there?

A
  1. Voltage Gated
  2. Ligand gated (GTP)
  3. Thermosensitive
  4. Mechanosensitive
42
Q

Describe Phase 1 of depolarization.

A

Na+ and K+ channels are closed, but there are some leaky K+ channels

43
Q

Describe Phase 2 of depolarization.

A

When the membrane gets depolarized, Na+ channels start to open (Permeability for Na+ is increased)

44
Q

Why does the cell become more depolarized during Phase 2 of depolarization?

A

Because the Na+ channels are starting to open, letting more positive ions inside the cells, thus depolarizing it
(positive feedback loop)

45
Q

Describe Phase 3 of depolarization.

A

Na+ channels are open and a lot of ions flow inside the cells

46
Q

Describe Phase 4 of depolarization.

A

In Phase 4, Na+ channels are closed by the inactivation gates, and K+ channels open, letting K+ ions flow outside the cell.

47
Q

Describe Phase 5 of depolarization.

A

:(

48
Q

Where does the initial action potential take place?

A

It happens at the soma (cell) and NEVER in the middle of the neuron
This is because the impulse must go only in one direction

49
Q

What does myelin prevent in terms of ion concentration?

A

Myelin prevents ion leaks

This is how the ion concentration gradient remains constant, very little to none is lost over a distance.

50
Q

Why is diffusion faster in myelinated axons?

A

The concentration difference is maintained and the ions will be more “willing” to move towards a low concentration gradient, as the differences remain high (hope this is understandable)

Neurosciences (7 decks)

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