Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

ESA 2- Membranes and Receptors > Electrical Excitability > Flashcards

Electrical Excitability Flashcards

1
Q

What is an action potential?

A

A change in voltage across a membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What does the action potential depend on?

A

Ionic gradients

The relative permeability of the membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is meant by action potentials being ‘all or nothing’?

A

There is no half, or double, action potentials etc

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What happens once an action potential has been generated?

A

It is propagated without loss of amplitude

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What happens once the membrane has been depolarised to threshold voltage?

A

Voltage gated Na channels open

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the effect of the opening of voltage gated Na channels?

A

It allows Na influx as Na ions attempt to move to their equilibrium potential

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the equilibrium potential of Na ions?

A

+61mV

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does the influx of Na ions cause?

A

It depolarises the membrane further, causing more voltage gated Na channels to open and even more depolarisation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

By what process does depolarisation cause more Na ion channels to open?

A

Positive feedback

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the positive feedback causing further Na channels to open to basis of?

A

The all or nothing characteristic of the action potential

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What happens in maintained depolarisation?

A

Na channels close by a mechanisms called inactivation

Voltage gated K channels are opened

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What happens when voltage gated K channels are opened?

A

There is K efflux, as K attempts to move towards its own equilibrium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the equilibrium potential of K?

A

-88mV

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What does the combination of K efflux and Na channel inactivation cause?

A

Repolarisation of the membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is happening in the upstoke of the action potenital?

A

Na channels open

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the result of the Na channels that open to cause depolarisation being voltage gated?

A

As the moment potential becomes more positive, positive feedback means that more channels will open until they all are

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Why can depolarisation not stop half way?

A

At any voltage above threshold, it will be at a voltage where more channels open, thus causing more depolarisation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is true of Na channels in the absolute refractory period?

A

Nearly all N channels are in the inactive state

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What level is excitability at in the absolute refractory period?

A

0

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is true of the Na channels in the relative refractory period?

A

They are recovering from inactivation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What happens to excitability in the relative refractory period?

A

It returns to normal as the number of channels in the inactivated state decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What happens as a stimulus gets longer?

A

A larger depolarisation is necessary to initiate an action potential

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Why does a longer stimulus mean a larger depolarisation is required to initiate an action potential?

A

Because Na channels become inactivated during the stimulus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

How are Na and Ca voltage gated channels similar?

A

In structure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Describe the structure of a Na/Ca voltage gated channel?

A

They main pore forming subunit is one peptide consisting of four homologous repeats.
Each repeat consists of 4 transmembrane domains

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What gives the Na/Ca channel its voltage sensitive properties?

A

One of the transmembrane domains is able to sense voltage across the membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What does a functional Na/Ca channel require?

A

One subunit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

How do voltage gated K channels compare to Na/Ca channels?

A

They are similar in structure, except each repeat is actually a separate subunit.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Describe the structure of voltage gated K channels

A

Each subunit has 6 transmembrane domains, one of which is voltage sensitive.

30
Q

What does a functional K channel require?

A

4 subunits

31
Q

Give an example of a local anaesthetic?

A

Procaine

32
Q

How do local anaesthetics act?

A

By binding to and blocking Na channels, thereby stopping action potential generation

33
Q

In what order to local anaesthetics block conduction in nerve fibres?

A

Small myelinated axons
Non-myelinated axons
Large myelinated axons

34
Q

What is the result of local anaesthetics blocking conduction in nerve fibres in the order that they do?

A

They tend to effect sensory before motor neurons

35
Q

What kind of molecules are local anaesthetics?

A

Weak bases

36
Q

How do localised anaesthetics cross the membrane?

A

In their unionised form

37
Q

When do local anaesthetics block the Na channels?

A

When the channel is open

38
Q

Do local anaesthetics have a high affinity to the activated or inactivated state of the Na channel?

A

Inactivated

39
Q

What are electrodes used for in extracellular recording of action potentials?

A

To raise the membrane to threshold to generate an action potential

40
Q

How can conduction velocity be calculated?

A

By recording changes in potential between the stimulating (cathode, -ve), and recording (anode, +ve) electrodes along an axon, and using the equation conduction velocity = distance / time

41
Q

What does the depolarisation of a small region of membrane produce?

A

Transmembrane currents in neighbouring regions

42
Q

What is the result of transmembrane currents being produced in neighbouring regions?

A

As Na channels are voltage gated, it opens more channels, causing propagation of the action potenital

43
Q

What happens if the local current spreads further?

A

The conduction velocity of the axon is faster

44
Q

What properties of an axon lead to a high conduction velocity?

A

A high membrane resistance
A high axon diameter
A low membrane capacitance

45
Q

Why does a high axon diameter lead to a high conduction velocity?

A

Has a low cytoplasmic resistance

46
Q

What is Ohm’s Law?

A

V=IR

47
Q

What does Ohm’s Law state?

A

The higher the resistance of the membrane, the higher the potential difference across it

48
Q

What does more voltage across the membrane result in?

A

More voltage gated Na channels being open

49
Q

What is the result of more voltage gated Na channels being opened?

A

It is easier to reach the threshold to fire an AP

50
Q

What effect does an increase in number of Na channels have on conduction velocity?

A

It increases it

51
Q

Why does large axon diameter increase conduction velocity?

A

Ohm’s Law states that the lower the resistance, the larger the current, and therefore the action potential will travel further, increasing action potential

52
Q

What is capacitance?

A

The ability to store charge

53
Q

What will a membrane with high capacitance do?

A

Take more current to charge, or a longer time for a given current

54
Q

What happens to a the time taken to charge in membrane with a low capacitance, for a given current?

A

It is shorter, thus increasing conduction velocity

55
Q

What happens to conduction velocity with myelination of axons?

A

It increases considerably

56
Q

What kind of axons are myelinated?

A

Large diameter axons, such as motor neurones

57
Q

What kind of axons are not myelinated?

A

Smaller ones, such as sensory neurones

58
Q

Why does myelination increase conduction velocity?

A

It reduces capacitance and increases membrane resistance of the axon

59
Q

What does myelination allow for?

A

Saltatory conduction

60
Q

What is saltatory conduction?

A

Where the AP ‘jumps’ between Nodes of Ranvier

61
Q

Why does saltatory conduction occur?

A

Because the myelin sheath acts as a good insulator, causing the local circuit current to depolarise the next node above threshold and generate an AP

62
Q

What do Nodes of Ranvier have?

A

High density of voltage gated Na channels

63
Q

How does Na channel density differ from Nodes of Ranvier in unmyelinated axons?

A

They have an even distribution of channels

64
Q

Which cells myelinate peripheral axons?

A

Schwann cells

65
Q

Which cells myelinate axons in the CNS?

A

Oligodendrocytes

66
Q

How do cells myelinate axons?

A

They envelop axons in their plasmalemma

67
Q

Give an example of a disease that strips areas of some axons of their myelin sheaths

A

Multiple Sclerosis

68
Q

What type of disease is MS?

A

Autoimmune

69
Q

What happens in MS?

A

Myeline is destroyed in certain areas of the CNS

70
Q

What effects can demyelination have?

A

Can have dramatic effects on the ability of previously myelinated axons to conduct action potentials properly, leading to decreased conduction velocity, complete block or cases where only some action potentials are transmitted

ESA 2- Membranes and Receptors (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions