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ICPP > The Action Potential > Flashcards

The Action Potential Flashcards

1
Q

What is an action potential? How long does it usually take?

A

A rapid change in the membrane potential

0.5ms in an axon

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2
Q

What is meant by the ‘all or nothing’ rule of action potentials?

A

Only occurs if a threshold level is reached

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3
Q

If sufficient depolarisation takes place and action potential will be initiated. Where do this occur?

A

At the axon hillock

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4
Q

If the conductance of an ion is increased, the membrane potential will move ________ the equilibrium potential for that ion

A

Towards

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5
Q

What causes an action potential to start?

A

A large increase in permeability to Na+ ions

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6
Q

What two channels are involved in an action potential?

A

Voltage dependent Na+ channels

Voltage dependent K+ channel

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7
Q

What does depolarisation do to voltage gated channels?

A

Open them

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8
Q

What does hyperpolarisation do to voltage dependent channels?

A

Close them

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9
Q

What happens to Na+ channels after they open?

A

They inactivate

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10
Q

Do K+ channels inactivate?

A

No

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11
Q

K+ channels are ______ in their closing causing ______

A

Delayed

Hyperpolarisation

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12
Q

How many ions need to flow to cause an action potential?

A

A small amount

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13
Q

What can be used to measure membrane currents at a set membrane potential?

A

Voltage clamps

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14
Q

Depolarisation is caused by…

A

An influx of sodium ions

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15
Q

Repolarisation is caused by….

A

Inactivation of sodium channels

(Slower) opening of K+ channels

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16
Q

Hyperpolarisation is caused by…

A

Increased K+ conductance

Delayed closing of K+ channels

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17
Q

What are the two periods of recovery for Na+ channels after an action potential? How long does each period last?

A

ARP - Absolute refractory period (1ms)

RRP - Relative refractory period (4ms)

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18
Q

What happens during the ARP?

A

Na+ channels inactivated
0 membrane excitability
No further action potentials can be sent

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19
Q

What happens during RRP?

A

Na+ channels recovering from inactivation
Recover once mp= -ve
Strong stimulus may result in action potential

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20
Q

What forms the functional part of a voltage gated Na+ channel?

A

1 peptide —-> 1 alpha subunit

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21
Q

What forms the functional part of a voltage gated K+ channel?

A

4 alpha subunits

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22
Q

How many repeats are found in a voltage gated Na+ channel?

A

4

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23
Q

How many repeats are found in a voltage gated K+ channel?

A

1

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24
Q

The 4th transmembrane region of each repeat on both voltage gated sodium and potassium channels contains…

A

Many positives amino acids, acts as a voltage sensor

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25
Q

What does a voltage gated Na+ channel contain to allow it to become inactivated?

A

An inactivation particle between repeats 3 and 4

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26
Q

Which region on both voltage gated sodium and potassium channels allows ions through?

A

The pore region

27
Q

Many local anaesthetics work by blocking the action of which channels? Give an example?

A

Na+ channels

Procaine

28
Q

Local anaesthetics block different axons in which order?

A

First… small myelinated axons —> unmyelinated axons —-> large myelinated axons

29
Q

What is the local current theory?

A

Injection of a current to one part of axon, will result in a spread of charge and therefore immediate changes and depolarisation of adjacent parts of the axon

30
Q

What is the length constant?

A

The distance it takes for the potential (of an injection of current) to drop to 37% of its original value

31
Q

_______ membrane resistance = increased conduction velocity/spread of charge

A

Increased

32
Q

________ membrane capacitance = increased conduction velocity/spread of charge

A

Decreased

33
Q

What is capacitance?

A

A property of the lipid bilayer (ability to store charge)

34
Q

What does resistance of a membrane depend upon?

A

The number of open channels

E.g. High resistance = less channels open

35
Q

Why does high capacitance result in decreased conduction velocity?

A

Voltage changes more slowly in response to current injection

36
Q

What affect does high resistance have on the spread of charge?

A

Spreads further along the axon

37
Q

What is responsible for the propagation of the action potential?

A

Local currents

38
Q

How does myelination increase the conduction velocity?

A

Increases membrane resistance

Decreases membrane capacitance

39
Q

The myelin sheath is produced by which cells in the PNS?

A

Schwann Cells

40
Q

The myelin sheath is produced by which cells in the CNS?

A

Oligodendricytes

41
Q

There is a high density of _______ at the nodes of Ranvier of myelinated axons

A

Na+ channels

42
Q

How are Na+ channels distributed along an unmyelinated axon?

A

Evenly

43
Q

What does saltatory conduction describe? What does it result in?

A

The jumping of the local circuit current from node to node

Increased conduction velocity

44
Q

In a myelinated axon, the diameter is ______ to the conduction velocity

A

Proportional

45
Q

In an unmyelinated axon, the conduction velocity is proportional to ______ of the diameter

A

Square root

46
Q

What is an example of a demyelinating disease? Which nerves does it affect? What does it result in?

A

Multiple sclerosis

Affects all cns nerves

Poorer transmission of action potentials (doesn’t reach threshold)

47
Q

What is a neuromuscular junction?

A

The synapse between a nerve and skeletal muscle cell (fibre)

48
Q

What channels are present at NERVE TERMINALS?

A

Voltage gated Na+ channels
Voltage gated K+ channels
A high density of voltage gated Ca2+ channels

49
Q

What does the opening of voltage gated calcium channels at nerve terminals result in?

A

Calcium into the cell

Release of neurotransmitter

50
Q

What does an increased frequency of action potentials result in?

A

Increases calcium entry at nerve terminals

More transmitter released

Bigger response

51
Q

What is the structure of a voltage gated Ca2+ channel?

A

Similar to structure of Na+ channel

1 alpha subunit makes a function channel

52
Q

What effect does nifedipine have on calcium channels? What is used to treat?

A

Blocks L type calcium channels

High blood pressure

53
Q

A pore forming alpha subunit is necessary for a functional channel, what is the function of other subunits?

A

They regulate the activity of the channel through phosphorylation/glycosylation of parts of the sub unit

54
Q

How do calcium channels activate/inactivate in comparison to sodium channels?

A

More slowly
At more positive membrane potentials

Inactivate more slowly as well

55
Q

What is voltage gated calcium channel inactivation dependent on?

A

The intracellular concentration of calcium

56
Q

During neurotransmitter release what does calcium bind to after its entry into the cell? What does this result in?

A

Synaptotagmin

Vesicle is brought close to the membrane?

57
Q

What happens for a vesicle of neurotransmitter to be released at a membrane?

A

Snare complex makes a fusion pore at the membrane

Transmitter released through the pore

58
Q

How are nicotinic acetylcholine receptors activated?

A

Binding of two molecules of ACh —> conformational change

Channels opens to Na+ and K+ ions

59
Q

How does crurare cause paralysis?

A

Blocks transmission between nerve and muscle

60
Q

Nicotinic ACh receptors can be blocked by which two methods, give an example of a drug that acts by each method?

A

Competitive blocker (tubocurarine)

Depolarising blocker (succinylcholine)

61
Q

How does competitive blocking of nicotinic ACh receptors by drugs such as tubocurarine work? How can it be overcome?

A

Blocking of ligand binding sites —> channel cannot open

Increasing [ACh]

62
Q

How does depolarising blocking of nicotinic ACh receptors by drugs such as succinylcholine work?

A

Binds to ligand binding sites activating the receptors and causing depolarisation

Stays bound, maintained depolarisation will not activate Na+ channels as they are inactivated

63
Q

What is mayasthenia gravis? What are its symptoms?

A

Autoimmune disease targeting nAChR

Muscle weakness and fatigue

ICPP (8 decks)

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