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Neurosciences > Synaptic Transmission > Flashcards

Synaptic Transmission Flashcards

1
Q

What do synapses do?

A

They connect two nerve cells and allow them to communicate

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2
Q

What two types of synapses are there?

A
  1. Electrical Synapse

2. Chemical Synapse

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3
Q

Describe the function of an electrical synapse

A

Electrical synapses perform a direct exchange of ions and small molecules by the passive flow between post and presynaptic cell

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4
Q

What are a few characteristics of an electrical synapse?

A
  1. Gap junction
  2. Extremely fast signal relay
  3. One-to-one transmission exchange
  4. Bi-directionality
  5. A signal is always transmitted because of the open pores
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5
Q

Describe the function of a chemical synapse

A

Chemical synapses use signaling molecules (neurotransmitters) to relay a message

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6
Q

What are the two signal translation steps in a chemical synapse?

A
  1. The Presynaptic cell releases neurotransmitters

2. The postsynaptic cell receives the neurotransmitters on a receptor and relays the signal

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7
Q

What happens after the post-synaptic receptors are activated?

A

Ions start flowing on the other side of the membrane

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8
Q

What are electrical synapses used for?

A

They are used in cellular networks for fast response and fast synchronization

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9
Q

What are a few characteristics of a chemical synapse?

A
  1. Cells are not in direct contact
  2. Neurotransmitters and receptors
  3. The signal can be regulated better (plasticity)
  4. There is not always a post-synaptic response
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10
Q

What are chemical synapses best used for?

A

Regulated neuronal activity.

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11
Q

Why is the ionic flow lower in the post-synaptic cell compared to the presynaptic cell?

A

Because there is some sort of resistance present that prevents the ions from flowing in as powerfully as the presynaptic cell.

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12
Q

What two types of receptors are present on the postsynaptic cell?

A
  1. Ligand-gated ion channels (ionotropic receptors)

2. G-protein-coupled receptors (metabotropic)

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13
Q

What properties should neurotransmitters have?

A
  1. stored in the presynaptic neuron
  2. should be released upon depolarization and calcium influx
  3. there should be very specific receptors on the postsynaptic neuron
  4. the neurotransmitters should only be active for a limited amount of time, after which it should be removed
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14
Q

Where would electrical synapses be important?

A

In places where reflexes are transmitted

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15
Q

What is meant by “plasticity” in chemical synapses signaling?

A
  1. Signals can be amplified
  2. Signals can be suppressed
  3. Signals can be altered
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16
Q

Describe the difference in biogenesis between small-molecule transmitters and peptide transmitters

A

Small molecule transmitters are locally recycled at the site of the synapse and do not require the Endoplasmatic Reticulum. Peptide Neurotransmitters on the other hand are produced in the cell’s ER and Golgi, then transported via vesicles by microtubules along the axon, to be released in the synapse.

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17
Q

What is the difference between small core vesicles and dense core vesicles?

A

Small core vesicles contain small molecules and dense core vesicles usually contain large molecules and peptides

18
Q

Why are recyclable neurotransmitters more often present?

A

So that fast signal relay is guaranteed. Peptide neurotransmitters can take days to reach the presynaptic cell.

19
Q

Roughly describe a synaptic vesical cycle

A
  1. Budding (from synaptic endosome)
  2. Docking (attachment to the membrane)
  3. Priming ( ready to be released)
  4. Fusion (fuses with membrane under the signal of Ca2+)
  5. Budding (Endocytosis)
20
Q

Why is it important that the amount of endocytosis and exocytosis in the synapse is in balance?

A

Because the membrane of the vesicle fuses with the cell membrane, the cell membrane will grow. There has to be a balance to prevent infinte expansion of the cell membrane

21
Q

What effect does the diameter of an axon have on signal velocity?

A

The wider the axon is, the faster a signal will be transduced (mostly present in aquatic animals, like frogs and squids)

22
Q

What is the readily releasable pool (RRP)?

A

The readily releasable pool is all the vesicles that are ready to be released

23
Q

Which three proteins are part of the SNARE group?

A
  1. Synaptobrevin
  2. Syntaxin
  3. SNAP-25
24
Q

What do the SNARE proteins do?

A

The SNARE proteins are a set of proteins that pull the presynaptic vesicle towards the membrane, to catalyze the fusion reaction.

25
Q

What is Synaptotagmin?

A

This protein is a Ca2+ sensor

26
Q

What prevents vesicles from fusing with the membrane without proteins?

A

The negative charge of the lipid bilayer is a repelling force that keeps the vesicles from fusing with the membrane

27
Q

On what structures are the three SNARE proteins found?

A
  1. Synaptobrevin is found on the vesicle itself and binds to the other two
  2. Syntaxin and SNAP-25 are found on the inside of the cell membrane and bind to the synaptobrevin
28
Q

How does Ca2+ lead to a fusion reaction?

A

Ca2+ binds to the Synaptotagmin molecules, which change the curvature of the membrane, bringing the two lipid bilayers together. Ca2+ then offers a positive charge to the molecule to neutralize the repelling negative charges, thus leading to fusion

29
Q

Why do only Small Vesicles get released in Low-Frequency stimulation? (Ca2+ signal frequency)

A

During Low-Frequency stimulation, only a small bit of calcium enters the cell to give a signal. This bit of calcium is quickly cleared away and only reaches the Small Vesicles that are primed on the membrane.

30
Q

Explain the difference between Low-Frequency and High-Frequency Calcium stimulation

A

During Low-Freq, the calcium that enters is quickly cleared away and doesn’t have the time to diffuse. During High-Freq, calcium enters and is cleared away, but doesn’t have enough time to clear all of it, so there will be some left. Multiple signals lead to calcium diffusing more in the cell.

31
Q

What types of vesicles are being released during High-Frequency stimulation?

A

Both Dense Core and Small Vesicles

32
Q

What are some characteristics of Dense Core vesicles?

A
  1. The core is really darkly stained and dense
  2. The Dense Core vesicles contain peptides and big molecules
  3. They do not recycle fast and require some sort of metabolism
  4. They require prolonged Ca2+ signaling to be released
33
Q

What do post-synaptic ion channels do, to let the ions in?

A

They change the permeability for an ion, so it goes in and relays a signal.

34
Q

What is End-Plate Current (EPC)?

A

the (macroscopic) current caused by all the open ion channels on the membrane

35
Q

What happens at a positive EPC?

A

A loss of positive ions or gain of negative ions to the cytoplasm

36
Q

What happens at a negative EPC?

A

A gain of positive charge or loss of negative charge to the cytoplasm

37
Q

What happens to the reversal potential when you elevate the extracellular concentration of K+?

A

There will be less of a driving force because the concentrations are less different.

38
Q

What are some characteristics of Excitatory Synapses?

A
  1. They are mainly operated by Glutamate

2. They operate mainly via Na+ and Ca2+ channels

39
Q

What are some characteristics of Inhibitory Synapses?

A
  1. They are mainly operated by GABA

2. They operate mainly via Cl- ion channels.

40
Q

What is meant by the summation of synaptic input?

A

To stimulate a post-synaptic neuron, you need a summation of all the synaptic input in order to evoke an action potential. This can be lowered by the number of inhibitory synapses and increased by the amount of excitatory synapses

Neurosciences (7 decks)

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