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202 - Theme 1 > Synaptic Transmission > Flashcards

Synaptic Transmission Flashcards

1
Q

What is a synapse?

A

A specialised junction where one part of a neuron contact and communicates with another neuron or cell type (muscle or glandular cell).

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2
Q

What are the two general categories of synapses?

A

Electrical and Chemical

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3
Q

Draw two diagrams, one showing an electrical synapse and one showing a chemical synapse.

A
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4
Q

What are the six properties of an electrical synapse?

A
  • Simpler structure and function
  • Faster
  • Passive signal transmission - This means that energy isn’t required for transmission, but it also means that a signal can’t be amplified.
  • Bidirectional
  • Minority, but particularly common in development(found in the adult retina)
  • Allow synchronised electrical activity among populations of neurons.
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5
Q

What are the three ways we classify synapses by location? Draw a simple diagram that shows them.

A
  1. Axodendritic
  2. Axosomatic
  3. Axoaxonic
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6
Q

What is synaptic weight, and give an example where a synapse, due to its location, would have a lot of it?

A

Synaptic weight is how potent a connection between two neurones is. An axosomatic neurone proximal to the axon hillock would have a larger synaptic weight than an axodendritic synapse.

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7
Q

How many neurones are there approximately in the human brain?

A

>80 billion

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8
Q

What is the ratio of neurones to glia?(Elaborate)

A

There is a ratio of glia to neurones of 1:1. This value has been fluctuating for 50 years.

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9
Q

How many synapses are there in the huma brain?

A

There are about 100 trillion(1014) synapses in the brain.

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10
Q

What is meant by the terms upstream and downstream when describing neurones?

A

upstream = presynaptic neuron

downstream = postsynaptic neuron

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11
Q

What are the six structures that make up the chemical synapse?

A
  1. synaptic button
  2. cytoskeleton
  3. mitochondria
  4. synaptic vesicles
  5. Active zone
  6. Synaptic cleft
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12
Q

How wide is the synaptic cleft of the chemical synapse and how does this compare with the electrical synapse?

A

The synaptic cleft is 20-50nm wide. Approximately, 10 times larger than the electrical synapse

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13
Q

How big are synaptic vesicles?

A

~50nm in diameter

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14
Q

What are secretory granules?

A

These are also known as dense-core vesicles; these contain neuropeptides.

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15
Q

How big are secretory granules?

A

100nm in diameters

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16
Q

Draw and label the neuromuscular junction.

A

There are also shallow folds at the motor-end plate to increase surface area to maximise electrical propagation.

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17
Q

What are the three ways neurotransmitters can affect the post-synaptic neuron?

A
  1. Excite the post-synaptic neurone via depolarisation
  2. Inhibit the post-synaptic neurone via hyperpolarisation
  3. Neuromodulation - this is where the neuron’s ability to release neurotransmitters is altered.
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18
Q

What are the four criteria for something to be a neurotransmitter?

A
  1. It must be synthesised in the neuron.
  2. It must be released and have a defined effect on the post-synaptic neuron/ effector organ.
  3. If a drug - It must mimic the actions of the neurotransmitter
  4. There must be a specific mechanism for it to be removed from the synapse.
19
Q

Describe what is happening at each step of the diagram.

A
20
Q

Where are vesicles stored before an action potential?

A

They are anchored to the cytoskeleton by synapsin.

21
Q

How do action potentials cause vesicles to dock at the active zone?

A
  1. An action-potential causes voltage-gated calcium channels to open, allowing an influx of calcium ions.
  2. Calcium activates calcium calmodulin activated kinase II (CaMKII)
  3. CaMKII phosphorylates synapsin to P-synapsin.
  4. P-Synpasin cannot bind to the cytoskeleton.
  5. Vesicles dock to the active zone.
22
Q

Draw a labelled diagram showing the release and recycling of synaptic vesicles.

A
23
Q

What does CaMKII stand for?

A

Calcium Calmodulin activate kinase II

24
Q

What do SNARE complexes do?

A

They dock vesicles to the plasma membrane.

25
Q

What does SNARE stand for?

A

Soluble NSF Attachment protein REceptor

26
Q

What does NSF stand for?

A

N-ethylmaleimide Sensitve Factor

27
Q

What are the two types of SNAREs?

A

T-SNAREs (Target)

V-SNAREs(Vesicles)

28
Q

What are the four complexes that make up the SNARE complex?

A
  1. Synaptotagmin
  2. Synaptobrevin
  3. Syntaxin
  4. SNAP-25 (SyNaptosome-Associated Protein of 25 kDa)
29
Q

What are the names of the 2 T-SNARES?

A
  1. Syntaxin(medially)
  2. SNAP-25(Laterally)
30
Q

What is the name of the V- SNARE?

A

Synaptobrevin

31
Q

Draw and label diagrams showing the four steps of docking and vesicle-membrane fusion.

A
32
Q

What does SNAP-25 stand for?

A

Synaptosome-associated protein of 25kDa

33
Q

What do clostridial toxins do?

A

They cleave SNARE complexes, preventing the docking synaptic vesicles and therefore inhibiting neurotransmitter release.

34
Q

What are the two main types of clostridial toxins?

A

Botulinum Toxin(BoTX)

Tetanus Toxin(TeTX)

35
Q

Where does the botulinum toxin(BoTX) act in the body?

A

At the neuromuscular junction, inhibiting Acetyl-choline release. This causes the muscle to be completely relaxed.

36
Q

Where does the Tetanus toxin(TeTX) act in the body?

A

At interneurons of the spine, inhibiting GABA and Glycine. This dis-inhibits muscles causing them to be permanently contracted.

37
Q

Name five diseases that affect the presynaptic neurone. How do they work?

A
  1. Congenital myasthenic syndromes - dues to issues of recycling vesicles - causes muscle weakness
  2. latrotoxin triggers membrane fusion
  3. Botulinum and tetanus toxin affect SNARE complexes.
  4. Cognitive disorders impair transsynapatic signalling.
  5. Lambert-Eaton myasthenic syndrome(LEMS) affects presynaptic calcium ion channels. causing muscle weakness
38
Q

What are the two types of membrane transporters in the presynaptic neuron?

A

Vesicle transporter

plasma membrane transporter

39
Q

How do vesicular transporters work?

A

ATPase proton pumps power them. These make the inside of the vesicle more acidic than the outside. An exchanger protein then exchanges a hydrogen ion for the neurotransmitter.

40
Q

How do plasma membrane transporters work?

A

They are powered by the electrochemical gradient. Two sodium ions are co-transported in with the neurotransmitter.

41
Q

Explain the concept of the tripartite synapse.

A

This expands the concept of synapses being only the pre and post-synapses but also includes the role of the glial cells. which release and respond to neurotransmitters.

42
Q

What four things do glia cells do? (Elaborate)

A
  1. They have receptors for neurotransmitters, and they can release calcium ions in response.
  2. They coordinate the formation of and elimination of synapses via secretion and cell surface associated signals.
  3. Aids in the recycling of neurotransmitters. for example glutamate to glutamine to the presynaptic neurone via the metabotropic glutamate receptor.
  4. Maintaining ion concentration via moderating potassium ions and pH.
43
Q

What are six examples of glial-derived diseases? Classify them as you go on.

A
  1. Reactive gliosis after injury
  2. Aberrant synapse formation - seen in epilepsy and neuropathic pain
  3. Brain cancer
  4. HIV-induced dementia
  5. Neuroinflammtory response in depression
  6. Aberrant synaptic stripping - causing Alzheimer’s, glaucoma and prion disease.
44
Q

Explain what signal integration is.

A

When combining numerous excitatory, inhibitory and modulating signals. What will be the overall effect?

202 - Theme 1 (2 decks)

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