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Techniques in Neuroscience > Introduction to electrophysiology > Flashcards

Introduction to electrophysiology Flashcards

1
Q

What is a resting membrane potential?

A

The voltage difference across the membrane of a neuron when at rest
-70 mVs intracellularly

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2
Q

What is the concentration gradient?

A

The concentration of positive or negative ions higher in one area than another

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3
Q

What is depolarisation?

A

Change in a neuron’s membrane potential that makes it more positive

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4
Q

What is hyperpolarisation?

A

Change in a neuron’s membrane potential that makes it more negative

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5
Q

What are ionotropic receptors?

A

Transmembrane proteins that form a channel allowing ions to travel in or out of a cell
- ligand-gated channel opens when receptor binds a ligand (e.g. NT)

Glutamate receptors and GABA-A receptors are ionotropic receptors

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6
Q

What are voltage-gated ion channels?

A

Transmembrane proteins that form ion channels whose opening and closing is regulated by the membrane potential near the channel

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7
Q

What is an action potential?

A

Process by which a neuron sends information down its axon

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8
Q

What are the 4 types of biological electrical activity?

A
  1. large voltages generated by animals
    - e.g. electric eels or rays: < 700V
  2. Negative resting membrane potential
    - most neurons: -70mV
  3. Postsynaptic potentials
    - small variable changes in membrane potential: 1-40mV
  4. Action potentials
    - large, fast, all or none: < 100mV
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9
Q

What are electroplaques?

A

Cells in animals that generate large voltages

- e.g. electric eels or rays

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10
Q

How are electroplaques activated?

A

By NT ion channel receptors:
When fish want to give electric shock, electroplaques are activated by a nerve which releases Ach onto nicotinic-type Ach receptors: ligand-gated receptors
-> flow of Na+ into electroplaques -> depolarises -> brief potential change of 120mV

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11
Q

What are the gradients corresponding to the force of diffusion and the electrostatic force?

A
  • Force of diffusion = concentration gradient

- Electrostatic force = electrical gradient

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12
Q

What happens to Na+ ions at resting membrane potential (Vmrest)?

A

Concentration and electrical gradients direct Na+ intracellularly

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13
Q

What happens to K+ ions at resting membrane potential (Vmrest)?

A

Concentration gradient directs K+ extracellularly despite inward electrical gradient

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14
Q

What happens to Cl- ions at resting membrane potential (Vmrest)?

A

Concentration gradient moves Cl- intracellularly despite outward electrical gradient

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15
Q

What happens to Ca2+ ions at resting membrane potential (Vmrest)?

A

Concentration and electrical gradients direct Ca2+ intracellularly

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16
Q

How are Excitatory postsynaptic potentials (EPSPs) generated?

A

By activation of ion channels that depolarise neurons

- Glu NT opens ion channel permeant to positive ions = inflow of Na+ and Ca2+

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17
Q

How are Inhibitory post synaptic potentials (IPSPs) generated?

A

By activation of ion channels that hyperpolarize neurons

- GABA NT opens ion channel permeant to negative ions = inflow of Cl-

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18
Q

Why are EPSPs and IPSPs graded in amplitude?

A

Due to the concentration of NT and length of time the NT is in the synaptic cleft

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19
Q

What are the stages of an action potential?

A
  1. Resting Vm
    - Na+ and K+ channels closed, resting
  2. Upstroke
    - Na+ channels open: Na+ goes in -> depolarisation
    - K+ channels closed, resting
  3. Peak
    - Na+ channels closed, inactivating
    - K+ channels opening
  4. Downstroke
    - Na+ channels closed, inactivated
    - K+ channels open: K+ moves out of cell -> hyperpolarisation
  5. Resting Vm
    - Na+ and K+ channels closed, resting
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20
Q

How does an action potential go down a neurons’ axon?

A

Depolarisation opens Na+ channels -> Na+ ions intracellularly -> further depolarisation -> further Na+ channels opening

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21
Q

What is a field potential?

A

The electric potential in the extracellular space around neurons

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22
Q

What is a nerve?

A

A bundle of axons

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23
Q

What is the compound axon potential?

A

The sum of the activity in a number of nerve fibres (axons)

- can be recorded extracellularly

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24
Q

What are the 5 versions of extracellular recording (ER)?

A
  1. Field potentials
  2. Whole nerve recordings
  3. Muticellular (multi-unit) recordings
  4. Single unit recordings
  5. Multi-electrode arrays (MEAs)
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25
Q

What is common to all versions of extracellular recording (ER)?

A

> The electrode is outside but close to the neurons

> The electrodes pick up only field potentials and low frequency filtered APs

> We cannot record Vmrest or postsynaptic potentials

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26
Q

What constitutes the technique of field potentials?

A
  1. Stimulating electrode
    - e.g. in hippocampus: activates Schaffer collaterals - NT released onto Purkinje neurons in CA1
  2. Recording electrodes pick up:
    - the field excitatory postsynaptic potential (fEPSP)
    - the somatic population spike AP (e.g. of CA1 cells in hippocampus)

=> We record the changes associated with changing membrane potentials of neurons (EPSP and resulting AP)

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27
Q

What is the field excitatory postsynaptic potential (fEPSP)?

A

Effect of glutamate receptors opening, causing depolarisation

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28
Q

What is the somatic population spike action potential?

A

Sum of many APs

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29
Q

What constitutes the technique of whole nerve activity?

A

> Nerve isolated and placed on platinum wires

  • outter chambers sealed with silicone grease, filled with olive oil to electrically isolate the nerve
  • > only the AP travelling down the axons (nerve) are recorded

> Stimulating electrodes increase the compound AP amplitude

  • the stronger the stimulation, the more axons are recruited to fire an AP
  • > Compound AP gets larger and eventually all axons will be recruited = maximal compound AP

> Can identify subgroups of axons by conduction velocity and stimulus threshold

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30
Q

In the technique of whole nerve activity, how can different axons recorded be separated?

A

By the intensity of the stimulus and their conduction velocity

31
Q

What constitutes the technique of multi-unit activity recording?

A

> Multi-unit extracellular recordings can be be done in vivo

> Electrode, e.g. placed in anaesthetised rat brain

> Stimulation (e.g. flash of light) to activate neurons

> Simultaneous recording of different neurons (e.g. one very close to electrode, the other further)

32
Q

What constitutes the technique of single unit activity recording?

A

> Stimulations to characterise single axon or neuron

> Comparison of the responses from the same single unit

33
Q

What constitutes the technique of multi-electrode arrays (MEAs)?

A

MEA electrodes are bedded in the bottom of a dish

  • 64 electrodes
  • inert to cells
  • pick up extracellular network electrical activity

> Neurons are grown inside these dishes, in an incubator

  • grow on the multi-electrode arrays
  • > monitoring of electrical activity (APs) in a non-invasive manner

> Characterises single axon or neuron

34
Q

What are the disadvantages of the field potentials technique?

A

> Cannot identify individual cells

> Cannot monitor PSPs or Vm

35
Q

What are the disadvantages of the whole nerve technique?

A

> Cannot identify individual cells

> Cannot monitor PSPs or Vm

36
Q

What is the disadvantage of the multi-unit technique?

A

Cannot monitor PSPs or Vm

37
Q

What are the disadvantages of the single unit technique?

A

> Difficult to do in vivo

> Cannot monitor PSPs or Vm

38
Q

What are the disadvantages of the technique of multi-electrode arrays (MEAs)?

A

> Cannot target particular cells
Only in vitro
Cannot monitor PSPs or Vm

39
Q

What is the common disadvantage of extracellular recording techniques?

A

Cannot monitor PSPs or Vm

40
Q

With intracellular recordings, what can the nature of the recording be?

A

> Current clamp
or
Voltage clamp

41
Q

With intracellular recordings, what can the nature of the recording electrodes be?

A

> Sharp electrodes
or
Patch clamp electrodes

42
Q

How are sharp electrodes used for intracellular recordings?

A

They penetrate the plasma membrane of the oocytes (animal’s egg)

43
Q

How are sharp electrodes used in a current clamp recording setup?

A

We change the current and record the voltage (AP)

44
Q

What is a current?

A

The rate at which an electric charge is flowing

45
Q

How are sharp electrodes used in a voltage clamp recording setup?

A

We stimulate with voltage and record the current

  • voltage induces the current that generates the AP
  • we record the current flow through the membrane that generates the voltage pulse (AP)
46
Q

How does the patch clamp technique work?

A

Patch clamp goes on the cell’s surface and interacts with the membrane
- forms a gigaseal on cell’s surface

47
Q

What are the 5 variants of the patch-clamp technique?

A
  1. On-cell patch
  2. Inside-out patch
  3. Whole-cell clamp
  4. Outside-out patch
  5. Perforated patch
48
Q

What characterises the on-cell patch technique?

A

Cell-attached patch recording:

- we record single ion channel activity

49
Q

What characterises the inside-out patch technique?

A

Membrane patch is off the cell
- access to intracellular side of the patch

-> we can apply drugs and record single channel activity

50
Q

What characterises the whole-cell clamp technique?

A

We break through the membrane with patch attached to the whole cell
- access to intracellular space -> record all ion channels in the cell’s membrane

> Whole cell patch clamp recording electrodes can be used in current-clamp and voltage-clamps mode

51
Q

What characterises the outside-out patch technique?

A

We pull off a small patch of membrane with 1 or 2 ion channels in it
-> outside of the membrane is exposed to extracellular space (normal for the cell)

52
Q

What characterises the perforated patch technique?

A

There is a pore forming antibiotic in electrode

  • we make a gigaseal on cell’s membrane, wait for the antibiotic to diffuse to the membrane
  • > membrane forms pores in itself

> Contents of cell are dialysed (separated) by electrode solution, BUT it still allows for electrical activity to be recorded

53
Q

With the perforated patch technique, why do you not loose the cell’s contents?

A

The whole on the cell’s membrane made by the antibiotic (from electrode) are small enough

54
Q

How can the whole cell patch clamp recording electrodes be used in voltage-clamp mode?

A

Acid stimulus:

  • pH change evokes acid-sensing ion channels (ASICs) that generate current when open
  • increasing acidity of the compounds increases the current’s size
55
Q

How can the whole cell patch clamp recording electrodes be used in current-clamp mode?

A

Intracellular calcium measurement
- Ca2+ entry during AP is related to number of APs activated in that cell

-> simultaneous recording intracellular Ca2+ levels and neuron’s APs

56
Q

How does the single channel recording technique work?

A

You can record a single channel conductance and measure its voltage dependance with voltage change in the channels

e.g.:
> Vp -10: cell depolarised by 10mV -> single channel conductance quite low, channel closed most of time

> Vp -20: one or both channels open ; increased activity ; channel current larger

> Vp -30: depolarised cell ; channel opened more ; more current

57
Q

What are the 4 consecutive modes of the in vivo patch clamp technique?

A
  1. Search mode
  2. “strike”
  3. Cell attached mode
  4. Whole cell mode
58
Q

What characterises the search mode of the in vivo patch clamp technique?

A

Positive pressure applied on the electrode
- forces air into electrode - pushes out fluid to keep path clear

-> the electrode can be moved through the tissue

59
Q

What characterises the “strike” mode of the in vivo patch clamp technique?

A

Electrode hits the cell -> pulse at heartbeat frequency

- we go back to a neutral pressure on the electrode

60
Q

What characterises the cell attached mode of the in vivo patch clamp technique?

A

Electrode giga-ohm seal is formed on cell’s membrane

61
Q

What characterises the whole cell mode of the in vivo patch clamp technique?

A

We’re sucking the solution up - suction on electrode
-> destroys the membrane patch made under the seal = whole cell mode

=> recording of sophisticated responses in vivo

62
Q

Which electrophysiology techniques can be applied on humans in vivo?

A

Only extracellular recording, as part of treatment

63
Q

Which electrophysiology techniques can be applied on non-humans in vivo?

A
  • Extracellular recording (implanted / anaesthetic)
  • Intracellular recording (anaesthetic)
  • Single cell recording (anaesthetic)
64
Q

Which electrophysiology techniques can be applied in vitro (including use of human tissue)?

A

Extracellular, intracellular, and single cell recording

65
Q

What is the disadvantage of the current clamp technique?

A

Cannot record voltage

66
Q

What is the disadvantage of the voltage clamp technique?

A

Unstable

67
Q

What are the advantages of the sharp electrode technique?

A
  • Reusable

- Simple electrode solution

68
Q

What are the disadvantages of the sharp electrode technique?

A
  • High resistance
  • Can be difficult to make
  • Some damage to cell
69
Q

What are the advantages of the patch electrode technique?

A
  • Low resistance
  • Relatively easy to make
  • Less damage to cell
70
Q

What are the disadvantages of the patch electrode technique?

A
  • Not reusable

- Complex electrode solution

71
Q

What are the advantages of the single channel technique?

A
  • Allows recording in real time of the functional activity of a single protein
  • Elucidates drug action at molecular level
72
Q

What is the disadvantage of the single channel technique?

A

Complex and lengthy analysis

73
Q

What are the advantages of the electrophysiological approach?

A

Electrophysiology is:

  • dynamic
  • functional
  • based on international system of units
  • real-time
  • high-fidelity and high temporal resolution

It can be used simultaneously or in conjunction with optical, molecular, biochemical and pharmacological approaches

=> essential to the understanding of the nervous system

Techniques in Neuroscience (6 decks)

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