Biology > Synapses > Flashcards

Synapses Flashcards

(44 cards)

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1
Q

What is a synapse?

A

The junction between a neurone and another neurone (or a neurone and an effector cell)

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2
Q

What is the gap between cells at a synapse known as?

A

The synaptic cleft

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3
Q

What does the presynaptic neurone have?

A

A swelling, called a synaptic knob

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4
Q

What does the synaptic knob contain?

A

Synaptic vesicles filled with chemicals called neurotransmitters

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5
Q

What happens when an action potential reaches the end of a neurone?

A

Causes neurotransmitters to be released into the synaptic cleft

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6
Q

What do neurotransmitters do once they have been released into the synaptic cleft?

A

Diffuse across to the postsynaptic membrane and bind to specific receptors
(might cause an action potential, muscle contraction, or hormone to be secreted)

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7
Q

How do synapses make sure impulses are unidirectional?

A

Receptors only found on postsynaptic membranes

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8
Q

How does the neurone ensure that the response doesn’t keep happening when neurotransmitters are in the synaptic cleft?

A

Neurotransmitters are removed

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9
Q

What is the neurotransmitter that we need to know about and what does it bind to?

A

Acetylcholine (ACh) - binds to cholinergic receptors

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10
Q

What are synapses that use ACh known as?

A

Cholinergic synapses

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11
Q

What are the 3 stages at cholinergic synapses?

A
  1. Arrival of an action potential
  2. Fusion of the vesicles
  3. Diffusion of Ash
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12
Q

What is the arrival of an action potential event at the presynaptic neurone in cholinergic synapses?

A
  • Action potential arrives at the synaptic knob
  • Stimulates voltage-gated calcium ion channels to open
  • Ca2+ diffuse into synaptic knob
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13
Q

What is the fusion of the vesicles event in cholinergic synapses?

A
  • Influx of Ca2+ into the knob cause synaptic vesicles to fuse with the presynaptic membrane
  • Vesicles release ACh into the synaptic cleft by exocytosis
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14
Q

In cholinergic synapses, what does ACh do after being released by the presynaptic neurone?

A

Diffuses across synaptic cleft and binds to specific cholinergic receptors on postsynaptic membrane

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15
Q

What does the binding of ACh to the postsynaptic membrane cause?

A

Na+ channels in neurone opens

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16
Q

What is the result of the Na+ channels opening in the postsynaptic neurone in cholinergic synapses?

A
  • Influx of Na+ into the membrane causes depolarisation
  • Action potential on the postsynaptic membrane is generated if threshold is reached
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17
Q

What happens to ACh after it has bound to cholinergic receptors (after some time)?

A

Removed from the synaptic cleft so response doesn’t keep happening

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18
Q

What is ACh broken down by and what happens to the products?

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A

Acetylcholinesterase
Products are re-absorbed by presynaptic neurone and used to make more ACh

19
Q

What are the 2 types of neurotransmitters?

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A

Excitatory and Inhibitory

20
Q

What are excitatory neurotransmitters?

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A

They depolarise the postsynaptic membrane, making it fire an action potential if the threshold is reached
(e.g. ACh)

21
Q

What are inhibitory neurotransmitters?

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A

Hyper polarise the postsynaptic membrane, preventing it from firing an action potential

22
Q

What is an example of an inhibitory neurotransmitter?

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A

GABA - when it binds to receptors, it causes K+ channels to to open on the postsynaptic membrane, hyper polarising the neurone

23
Q

What is an inhibitory synapse?

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A

A synapse where inhibitory neurotransmitters are released from the presynaptic membrane following an action potential

24
Q

What is summation at synapses?

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A

Where the effect of neurotransmitters released from many neurones (or one neurone thats stimulated a lot in a short period of time) is added together

25
What are the 2 types of summation?
Spatial and Temporal
26
What is spatial summation?
Where 2 or more presynaptic neurones release their neurotransmitters at the same time onto the postsynaptic neurone
27
What is the effect of spatial summation?
The small amount of neurotransmitter from each neurone can be enough altogether to reach the threshold in the postsynaptic neurone and trigger an action potential
28
What happens if some neurones release an inhibitory neurotransmitter in spatial summation?
The total effect of all neurotransmitters might be no action potential
29
What is temporal summation?
Where 2 or more nerve impulses arrive in quick succession from the same presynaptic neurone - must happen very quickly
30
Why does a temporal summation make an action potential more likely?
More neurotransmitter is released into the synaptic cleft
31
What is a neuromuscular junction?
Specialised cholinergic synapse between a motor neurone and a muscle cell
32
What do neuromuscular junction use?
Acetylcholine
33
What does acetylcholine bind to at neuromuscular junctions?
Cholinergic receptors, known as nicotine cholinergic receptors
34
How do neuromuscular junctions work?
In the same way as cholinergic synapses
35
How is ACh broken down at neuromuscular junctions?
In the synaptic cleft by the enzyme acetylcholinesterase (AChe)
36
What are the differences at the postsynaptic membrane of a neuromuscular junction compared to that of a cholinergic synapse?
- At a neuromuscular, membrane has lots of folds that form clefts - These cleft store AChe - membrane has more receptors
37
What is normally the result in a neuromuscular junction when a motor neurone fires an action potential and why?
Normally triggers a response in a muscle cell - ACh is always excitatory (isn't always the case for a synapse between 2 neurones
38
What can drugs affect?
Synaptic transmission
39
What are the various ways drugs can affect synaptic transmission?
Same shape as neurotransmitters Block receptors Inhibiting enzymes Stimulating release of neurotransmitters Inhibiting release of neurotransmitters
40
How do drugs the same shape as neurotransmitters affect synaptic transmission?
Mimic their action at receptors so more receptors are activated - these drugs known as agonists
41
How do drugs that block receptors affect synaptic transmission?
Receptors can't be activated by neurotransmitters - these drugs are called antagonists
42
How do drugs that inhibit enzymes affect synaptic transmission?
- Inhibit enzyme that breaks down neurotransmitters - More of them in the synaptic cleft to bind to receptors - There for longer as well
43
How do drugs that stimulate release of neurotransmitters affect synaptic transmission?
Stimulate release from presynaptic neurone so more receptors activated
44
How do drugs that inhibit release of neurotransmitters affect synaptic transmission?
Inhibit release from presynaptic neurone so fewer receptors activated
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