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NSB Lectures > Physiology of neurons > Flashcards

Physiology of neurons Flashcards

1
Q

Which ions are predominantly extracellular?

A

Na & Cl-

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2
Q

Is the extracellular space negative or positive?

A

Positive

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3
Q

Is the inside of the cell negative or positive?

A

Strongly negative

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4
Q

What largely determines the charge of the inside of the cell?

A

The amount of K+ ions and also intracellular proteins

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5
Q

Why is it hard for charged ions to cross the cell membrane?

A

The cell membrane is hydrophobic - this means it hates charged particles and they cannot cross

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6
Q

What is the difference between a concentration gradient and an electrochemical gradient?

A

Concentration gradients = ion movement is driven across the membrane by higher concentrations of the ion on one side than the other.

Electrochemical gradients = ion movement is driven by charge differences - large concentrations of similarly charged particles cause repulsion and give them the desire to move to an area where there are less particles of that charge

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7
Q

Can any ion cross a leak channel?

A

No - they are selective for a particular ion

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8
Q

Do leak channels allow fast transfer of ions?

A

They allow slow transfer of K+ and Na+

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9
Q

What types of ion cross the membrane via leak channels?

Which does the cell have more of?

What does it mean for resting potential?

A

Cell has K+ and Na+ leak channels.

Most cells have more K+ than Na+ = more positive charge is removed from the cell - therefore resultant charge is more negative intracellularly at rest - so resting potential is negative.

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10
Q

What are leak channels?

A

Protein channels which open up periodically (and randomly) & allow certain ions to cross in small amounts.

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11
Q

What do Na leak channels do?

A

Allow Na to move into the cell (in small amounts)

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12
Q

What do K leak channels do?

A

Allow K to leave the cell (in small amounts)

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13
Q

What is the Na / K pump?

A

Protein channel that moves 3 Na+ ions out of the cell using ATP, and then pumps 2 K+ ions into the cell when the conformation changes back.

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14
Q

How does the Na / K pump work?

A

It breaks down ATP into ADP - and the energy released from this reaction is used to change the conformation (shape) of the channel allowing 3 Na+ to leave the cell. When the energy is used, the protein then changes shape back again - which allows 2K+ to re-enter the cell.

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15
Q

What is a voltage gated ion channel?

A

It is an ion channel that changes shape in response to changes in the voltage of the cell membrane.

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16
Q

What types of voltage gated channels exist in neurons?

A

K+ (Kv) and Na+ (Nav)

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17
Q

What is resting potential maintained by?

A

Leak channels and the Na/K membrane pump

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18
Q

What happens when there is depolarisation of the membrane?

A

The voltage gated Na channels open - lets a huge amount of Na+ into the cell - making the cell more positive (further depolarisation).

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19
Q

Why does depolarisation of the membrane cause Na voltage gated channels to open?

A

Inside Na voltage gated channel proteins are positive elements. These are strongly attracted to the negative inner of the cell. When the inside of the cell becomes less negative, the elements in the channel become less attracted, and therefore they allow the protein channel to move and change shape - thereby “opening” the channel and allowing free flow of ions through it.

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20
Q

What happens when there is a lot of depolarisation of the cell membrane (+40mV)?

A

The voltage-gated K+ channels can open - allowing an influx of K+ ions out of the cell - thereby making the inside of the cell more negative again.

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21
Q

What are mechanically-gated ion channels?

A

Ion channels that are opened by a mechanical stimulus (e.g. tissue stretching).

22
Q

How do mechanically-gated ion channels work?

A

The mechanical stimulus causes the channel to undergo conformational change and open.

23
Q

What are ligand-gated ion channels?

A

Ion channels that opens when the ligand (chemical) binds to the target receptor on the channel.

24
Q

What is an electrochemical gradient?

A

The electrical force that drives ions to move (from an area of similar charge to an area of different charge) and the chemical force that drives ions to move by diffusion from an area of high concentration to low concentration.

25
Q

Which are the most important ions in determining membrane potential?

A

Na+, Cl- & K+

26
Q

What affects the movement of ions across a membrane?

A

The permeability of the membrane to that ion.

27
Q

What is the permeability of the membrane controlled by for the ions Na+ and K+?

A

Protein channels - inc leak channels and the Na/K pump.

28
Q

What is another name for the Na+/K+ pump?

A

Na+/K+ ATPase

29
Q

What voltage is resting potential?

A

-70mV

30
Q

How are action potentials generated?

A

Depolarisation of the membrane occurs (usually as a result of stimulus from nearby cells). This depolarisation causes the inside cytoplasm of the cell to become less negative.

When the cytoplasm becomes less negative, the voltage sensing elements in the centre of the Na+ channels become far less strongly attracted to the cytoplasm (they are positively charged) and this means they move away and allow the Na channel to change shape.

When the Na channel changes shape (voltage gated channel) - it allows a huge influx of Na+ ons into the cell - making the cell inside EVEN MORE positive = DEPOLARISATION. This is rapid.

When the cell reaches about +40mV, an action potential is triggered, the Na+ channels close and the K+ channels open. This allows an outward flow of K+ ions to the extracellular space = REPOLARISATION.

The amount of ions that flow out is so great the cell becomes HYPERPOLARISED - -90mV.

The K+ voltage gated ion channels then close, and the cell returns to resting potential via leak channels and the Na/K+ ATPase pump.

31
Q

What things can cause depolarisation to occur in a nerve cell?

A
  • Signal received at the dendrites.
  • Nearby cell depolarising
  • Signal received via neurotransmitters (NT)
32
Q

What does it mean when we say an AP is binary?

A

It is all or nothing - it either meets the depolarisation threshold and occurs, or it does not and no AP occurs. When then the depolarisation reaches around -50mV, the neuron is committed to the action potential.

33
Q

What is the refractory period?

A

When the neuron gets hyperpolarised (below -70mV), it cannot respond to a fresh stimulus of depolarisation and therefore another AP cannot fire.

34
Q

During the refractory period - why can the neuron not respond to a new stimulus?

A

Because the inside of the cell is extra negative during hyper polarisation. This means that the voltage sensing elements within the Na+ voltage gated channels are STRONGLY attracted and this pull keeps the channel closed. It is only when the cell returns to resting membrane potential that these elements are less strongly attracted and can be stimulated to change shape.

35
Q

What is the electronic-potential of the following ions if they were freely allowed to move and were the only ions present?
- Na
- K
- Ca
- Cl

A

Na = +60mV
K = -90mV
Ca = 123
Cl = -40

36
Q

What adaptation of neurons allows for fast propagation of a signal?

A

Myelination & Nodes of Ranvier in between

37
Q

What is the difference between myelinated and unmyelinated cells in terms of polarisation?

A

Unmyelinated - depolarisation spreads uniformly - but is slower and travels at a speed of approx 10m/s

Myelinated - depolarisation jumps between nodes - increasing propagation velocity to about 120-150m/s

38
Q

What are the two types of synapse?

A

Chemical & electrical

39
Q

What are electrical synapses?

A

They are PHYSICALLY CONNECTED synapses - allows the waves of depolarisation & AP to pass through.

40
Q

What are chemical synapses?

A

Not physically connected - instead when the AP arrives at the pre-synaptic terminal, it stimulates vesicles to bind to the membrane and release NTs into the synapse. These then bind to ligand-gated ion channel receptors on post-synaptic membrane and initiate depolarisation of the post-synaptic membrane.

41
Q

Name one other type of potential apart from action potential.

A

Graded potential

42
Q

The following details an action potential - how does a graded potential differ from this?

AP -
- needs a big change in voltage to start - therefore need a large, defined stimulus.
- need depolarisation to begin.
- are very short (1ms)
- are all or nothing (binary) - amplitude is not proportional to the signal produced
- must meet threshold to commence
- demonstrates large amplitude of response
- AP can travel far without weakening
- has a refractory period

A

GP
- only requires a small deviation from the resting potential;
- can be caused by depolarisation or hyperpolarisation,
- are slower and last longer than APs;
- no threshold needs to be met to initiate - therefore not binary - rather amplitude is proportional to the signal
- less amplitude than APs.
- GP doesn’t travel far, only short distances and weakens as it goes
- has no refractory period (change in voltage is usually small)

43
Q

What is depolarisation?

A

When the cell becomes less negative (more positive).

44
Q

What is hyperpolarisation?

A

When the cell becomes more negative (less positive).

45
Q

What is it called when a signal weakens as it progresses along?

A

Decremental conduction

46
Q

Can graded potentials cause an AP to occur?

A

If the graded potentials are large enough - they can lead to an AP.

GPs can also be summated (added together) - increases the amplitude and if high enough can initiate an AP.

47
Q

What often initiates a graded potential?

A

A ligand or mechanical-gated ion channel

48
Q

What is Carbamazepine used for?

A

Anticonvulsant

49
Q

How does Carbamazepine work?

A

Binds to & inhibits voltage-gated Na channels (does so by binding to the channel when it is inactive and raising the threshold required for an AP so the channel cannot open).

∴ Doesn’t inhibit entirely - rather it raises threshold needed for AP.

50
Q

What is Lidocaine used for?

A

Topical anaesthetic

51
Q

How does Lidocaine work?

A

Binds to & inhibits Na voltage-gated ion channels in pain neurons.

Inhibits local APs by raising threshold required for AP.

52
Q

What is Sodium Valproate used for?

A

Anti-epileptic drug + used for treating bipolar

NSB Lectures (48 decks)

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