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A-level Biology > 6B - Synaptic transmission > Flashcards

6B - Synaptic transmission Flashcards

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1
Q

What is a synapse?

A

A junction between a neurone and the next cell (another neurone or an effector cell - muscle or gland cell).

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2
Q

What is the tiny gap between the cells at a synapse called?

A

The synaptic cleft.

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3
Q

What is the swelling on the presynaptic neurone called?

A

A synaptic knob.

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4
Q

What does the synaptic knob contain?

A

Synaptic vesicles.

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5
Q

What are synaptic vesicles filled with?

A

Chemicals called neurotransmitters.

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6
Q

When an AP reaches the end of a neurone it causes what?

A

Neurotransmitters to be released into the synaptic cleft.

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7
Q

Where are neurotransmitters released from?

A

Synaptic vesicles.

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8
Q

Where are neurotransmitters released to?

A

The synaptic cleft.

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9
Q

What do neurotransmitters do once released into the synaptic cleft?

A

They diffuse across to the postsynaptic membrane and bind to specific receptors.

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10
Q

What do neurotransmitters bind to?

A

Specific receptors on the postsynaptic neurone.

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11
Q

What happens when neurotransmitters bind to receptors in the postsynaptic neurone?

A

They might trigger an AP in a neurone, cause muscle contraction in a muscle cell, or cause a hormone to be secreted from a gland cell.

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12
Q

What is the benefit of receptors only being on the postsynaptic membranes?

A

Synapses make sure impulses are unidirectional - the impulse can only travel in one direction.

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13
Q

What does it mean is an impulse is unidirectional?

A

It can only travel in one direction.

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14
Q

What makes sure that impulses are unidirectional?

A

The receptors being only on the postsynaptic membranes.

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15
Q

Why are neurotransmitters removed from the cleft?

A

So the response doesn’t keep happening.

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16
Q

What happens to neurotransmitters when they are removed from the cleft?

A

they are taken back into the presynaptic neurones or they are broken down by enzymes and the products are taken into the neurone.

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17
Q

What happens to neurotransmitters in the cleft?

A

They are removed.

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18
Q

Give examples of neurotransmitters

A

Acetylcholine (ACh) and noradrenaline.

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19
Q

What are synapses that use acetylcholine called?

A

Cholinergic synapses.

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20
Q

What does ACh stand for?

A

Acetylcholine

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21
Q

What is acetylcholine shortened to?

A

ACh

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22
Q

What does ACh do?

A

Transmits the nerve impulse across a cholinergic synapse.

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23
Q

What is a cholinergic synapse?

A

A synapse that uses acetylcholine.

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24
Q

Explain how a nerve impulse is transmitted across a cholinergic synapse

A

1) An AP arrives at the synaptic knob of the presynaptic neurone.
2) This AP stimulates voltage-gated calcium ion channels in the presynaptic neurone to open.
3) Calcium ions diffuse into the synaptic knob (they’re pumped out afterwards by active transport).
4) The influx of calcium ions into the synaptic knob causes the synaptic vesicles to move to the presynaptic membrane. They then fuse with the presynaptic membrane.
5) The vesicles release acetylcholine into the synaptic cleft - this is called exocytosis.
6) ACh diffuses across the cleft and binds to specific cholinergic receptors on the postsynaptic membrane - binds to receptors on the sodium ion protein channels.
7) This causes the sodium ion channels in the postsynaptic neurone to open - sodium ions diffuse into the postsynaptic neurone.
8) The influx of sodium ions into the postsynaptic membrane causes depolarisation. An AP on the postsynaptic membrane is generated if the threshold is reached.
9) ACh is removed from the synaptic cleft so the response doesn’t keep happening. It is hydrolysed by an enzyme called acetylcholinesterase (AChE) into ethanoic acid (acetyl) and choline. These diffuse back back across the cleft and and re-absorbed by the presynaptic neurone.
10. ATP released from the mitochondria is used to recombine choline and ethanoic acid to acetylcholine.

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25
Q

What is acetylcholine broken down (hydrolysed) into?

A

Ethanoic acid (acetyl) and choline.

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26
Q

What enzyme hydrolyses acetylcholine?

A

Acetylcholinesterase (AChE).

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27
Q

What is acetylcholinesterase and what does it do?

A

It is an enzyme that breaks down acetylcholine into ethanoic acid (acetyl) and choline.

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28
Q

What types of neurotransmitters are there?

A

Excitatory, inhibitory and both.

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29
Q

What do excitatory neurotransmitters do to the postsynaptic membrane?

A

Depolarise it, making it fire an AP if the threshold is reached.

30
Q

When is acetylcholine an excitatory neurotransmitter?

A

Excitatory at cholinergic synapses in the CNS and at neuromuscular junctions.

31
Q

Why is acetylcholine an excitatory neurotransmitter at cholinergic synapses in the CNS?

A

It binds to receptors to cause an AP in the postsynaptic membrane.

32
Q

What do inhibitory neurotransmitters do to the postsynaptic membrane?

A

Hyperpolarise it (making the potential difference more negative), preventing it from firing an AP.

33
Q

When is acetylcholine an inhibitory neurotransmitter?

A

Inhibitory at cholinergic synapses in the heart.

34
Q

What type of neurotransmitter is acetylcholine?

A

Both excitatory and inhibitory.

35
Q

Why is acetylcholine an inhibitory neurotransmitter at cholinergic synapses in the heart?

A

When it binds to receptors here, it can cause potassium ion channels to open on the postsynaptic membrane, hyperpolarising it.

36
Q

What happens in terms of neurotransmitters if a stimulus is weak?

A

Only a small amount of neurotransmitter will be released from a neurone into the synaptic cleft. This might not be enough to excite the postsynaptic membrane to the threshold level and stimulate an AP.

37
Q

What is summation?

A

Where the effect of a neurotransmitter released from many neurones (or one neurone that’s stimulated a lot in a short period of time) is added together.

38
Q

How many types of summation are there?

A

2

39
Q

What are the 2 types of summation?

A

Spatial summation and temporal summation.

40
Q

Explain spatial summation

A

1) Sometimes many neurones connect to one neurone.
2) The small amount of NT released from each of these neurones can be enough altogether to reach the threshold in the postsynaptic neurone and trigger an AP.
3) If some neurones release an inhibitory NT then the total effect of all the NT’s might be no AP.

41
Q

When in terms of spatial summation will there be an AP?

A

If many neurones release enough NT.

42
Q

When in terms of spatial summation will there not be an AP?

A

If there are more inhibitory NT released (-) than excitatory NT’s (+).

43
Q

What is temporal summation?

A

Where 2 or more nerve impulses arrive in quick successions from the same presynaptic neurone.

44
Q

Why does temporal summation make an AP more likely?

A

Because more NT is released into the synaptic cleft.

45
Q

When is an AP produces in terms of temporal summation?

A

If there is a high frequency of weak impulses produced.

46
Q

What do both types of summation mean for the response they cause?

A

Means synapses accurately process information, finely tuning the response.

47
Q

What are neuromuscular junctions?

A

Synapses between a motor neurone and a muscle cell.

48
Q

What NT do neuromuscular junctions use?

A

Acetylcholine.

49
Q

What does ACh bind to in a neuromuscular junction?

A

Cholinergic receptors called nicotinic cholinergic receptors.

50
Q

What are the differences between the way in which a neuromuscular junction works in comparison to a cholinergic synapse in the CNS?

A
  • The postsynaptic membrane has lots of folds that form clefts. These clefts store the enzyme that breaks down ACh (AChE).
  • The postsynaptic membrane has more receptors than other synapses.
  • ACh is always excitatory at a neuromuscular junction. So when a motor neurone fires an AP, it normally triggers a response in a muscle cell. This isn’t always the case for a synapse between two neurones.
51
Q

What do the folds that form clefts (in a neuromuscular junction) do?

A

Store the enzyme that breaks down Ach (acetylcholinesterase - AChE).

52
Q

Do neuromuscular junctions or cholinergic synapses have more receptors on the postsynaptic membrane?

A

Neuromuscular junctions.

53
Q

Is ACh excitatory or inhibitory at a neuromuscular junction?

A

Always excitatory.

54
Q

Explain what happens because ACh is always excitatory at a neuromuscular junction.

A

So when a motor neurone fires an AP, it normally triggers a response in a muscle cell. This isn’t always the case for a synapse between two neurones.

55
Q

What is the postsynaptic membrane in a neuromuscular junction also called?

A

The motor end plate.

56
Q

In what ways can drugs affect the action of NT’s at synapses?

A
  • Some are the same shape as the NT so they mimic their action at receptors.
  • Some block receptors so they can’t be activated by NT.
  • Some inhibit the enzyme that breaks down NT.
  • Some stimulate the release of NT from the presynaptic neurone so more receptors are activated.
  • Some inhibit the release of NT for fewer receptors are activated.
57
Q

How does some drugs being the same shape as neurotransmitters affect the action of neurotransmitters at synapses?

A

They mimic their action at receptors. This means more receptors are activated.

58
Q

What are drugs that are the same shape as NT that mimic their action at receptors called?

A

Agonists.

59
Q

What are agonists (drugs)?

A

Drugs that are the same shape as NT that mimic their action at receptors.

60
Q

Give an example of how drugs being the same shape as NT affects NT action

A

Nicotine mimics acetylcholine so binds to nicotinic receptors in the brain.

61
Q

How do drugs that block receptors affect the action of neurotransmitters at synapses?

A

The receptors can’t be activated by NT. This means that fewer receptors (if any) can be activated.

62
Q

What are drugs that block receptors called?

A

Antagonists.

63
Q

What are antagonists (drugs)?

A

Drugs that block receptors.

64
Q

Give an example of how drugs that block the receptors affect NT action

A

Curare blocks the effects of acetylcholine by blocking nicotinic cholinergic receptors at neuromuscular junctions, so muscle cells can’t be stimulated. This results in the muscle being paralysed.

65
Q

How do drugs that inhibit the enzyme that breaks down NT affect the action of neurotransmitters at synapses?

A

They stop the enzyme from working, This means that there are more NT in the synaptic cleft to bind to receptors and they’re there for longer.

66
Q

Give an example of how drugs that inhibit the enzyme that breaks down NT affect NT action

A

Nerve gases stop acetylcholine from being broken down in the synaptic cleft. This can lead to loss of muscle control.

67
Q

How do drugs that stimulate the release of NT from the presynaptic neurone affect the action of neurotransmitters at synapses?

A

More receptors are activated.

68
Q

Give an example of drugs that stimulate the release of NT from the presynaptic neurone affect NT action

A

Amphetamines.

69
Q

How do drugs that inhibit the release of NT from the presynaptic neurone affect the action of neurotransmitters at synapses?

A

Fewer receptors are activated.

70
Q

Give an example of drugs that inhibit the release of NT from the presynaptic neurone affect NT action

A

Alcohol.

A-level Biology (42 decks)

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