Synaptic Transmission

Question 1

Do chemical or electrical synapse provide a faster transmission of a signal?

Answer 1

• electrical synapse: pre and post synaptic membrane are physically connected via gap junctions

Question 2

Do chemical or electrical synapse have more biological flexibility?

Answer 2

• chemical

Question 3

What is the name given to where the pre and post synapse meet in an electrical synapse?

1. gap junctions made from connexin36
2. gap junctions made from tight junction
3. synaptic cleft made from connexin36
4. synaptic cleft made from tight junction

Answer 3

1. gap junctions made from connexin36
   - essentially holes for ions to flow through

Question 4

Electrical synapses are connected by gap junctions between the pre and post synapse. They are gap junctions that connect the pre and post synapse at electrical synapse composed of connexin 36. How many subunits do these gap junctions have?

1. 1
2. 3
3. 6
4. 9

Answer 4

3. 6
   - referred to as a connexon

Question 5

When an action potential travels down the pre-synpatic terminal and transfers it to the post synapse, what is this action potential then called?

1. pre-synaptic termination
2. post-synaptic termination
3. post-synaptic potential
4. excitatory post synaptic potential

Answer 5

3. post-synaptic potential (PSP)

• can also be referred to as a post-synaptic potential (PSP)
• causes change in voltage in post-synaptic cell and an action potential occurs

Question 6

If a cell receives a postsynaptic potential (PSP) in the post synaptic cell, will this be sufficient to generate an action potential in the post synaptic cell if it only generates 1mV?

Answer 6

• no
• requires synaptic integration from lots of graded potentials
• an action potential follows

Question 7

In a chemical synapse, what is the gap between the pre and post synapse called?

Answer 7

• synaptic cleft
• aprox 30nm wide

Question 8

In a chemical synapse, what is an active zone?

1. site where neurotransmitters bind
2. site of neurotransmitter release
3. site where neurotransmitters are made
4. site where neurotransmitters are recycled

Answer 8

2. In Chemical synapse

active zone is site of

neurotransmitter release

Question 9

There are 3 locations on a neuron where chemical synapses can take place, including the soma, dendrites or axon. Label the 3 sites using the labels below:

• axondendritic synapse (axon to dendritic)
• axonsomatic synapse (axon to soma)
• axoaxonic synapse (axon to axon)

Answer 9

a = axondendritic synapse (axon to dendritic)

b = axonsomatic synapse (axon to soma)

c = axoaxonic synapse (axon to axon)

Question 10

Are there more chemical or electrical synapse in the body?

Answer 10

• chemical

Question 11

Where are small molecule neurotransmitters synthesised?

1. pre-synaptic terminal
2. axon hillock
3. cell body
4. axon

Answer 11

1. pre-synaptic terminal

Question 12

Where are neuropeptides neurotransmitters synthesised?

1. pre-synaptic terminal
2. axon hillock
3. cell body
4. axon

Answer 12

4. cell body

Question 13

Once neurotransmitters have been synthesised in the cell body of the neuron, where are they transported to and found in their highest concentrations?

1. pre-synapse
2. axon hillock
3. cell body
4. axon

Answer 13

1. pre-synapse

Question 14

Once neurotransmitters are released at the pre synapse, do they randomly bind to any receptor?

Answer 14

• no
• selectively bind to specific targets

Question 15

To be characterised as a neurotransmitter, if a neurotransmitter is administered, what should it do to its target receptors?

Answer 15

• should mimic the endogenously released ligand

Question 16

To be characterised as a neurotransmitter, if a neurotransmitter is released into the synaptic cleft, what must happen to the neurotransmitter once the action potential has finished?

Answer 16

• it will be removed/recycled from the synaptic cleft

Question 17

Large neuropeptide neurotransmitters and small peptide neurotransmitters are synthesised in the cell body and pre-synaptic terminal, respectively, before being transported to the pre-synapse where they can be found in the highest concentrations. What does the neuronal cell use to transport the vesicles containing the neurotransmitters along the microtubules to the pre synapse?

1. kinesin Antegrade (away from the cell body)
2. dynenin Retrograde (to the the cell body)
3. kinestain Retrograde (away from the cell body)
4. dynenin Retrograde (away from the cell body)

Answer 17

1. kinesin Antegrade (away from the cell body)

Question 18

Neurotransmitters that are produced in the cell body and then transported to the pre synapse by kinesin along the microtubules, which is referred to as Antegrade (AWAY from cell body). They can also be recycled and may need to travel back to the cell body. What does the neuronal cell use to transport the vesicles containing the neurotransmitters along the microtubules back to the cell body?

1. kinesin Antegrade (away from the cell body)
2. dynenin Retrograde (to the the cell body)
3. kinestain Retrograde (away from the cell body)
4. dynenin Retrograde (away from the cell body)

Answer 18

2. dynenin Retrograde (to the the cell body)

Question 19

Once an action potential is received at the pre synapse, what channels open to allow vesicles containing neurotransmitters to fuse with the pre synapse membrane causing exocytosis of the neurotransmitter into the synaptic cleft?

1. Na+ channels
2. K+ channels
3. Ca²⁺ channels
4. Cl- channels

Answer 19

3. Ca²⁺ channels

Question 20

The active zone is the site where neurotransmitters are released at the pre synapse. Once the action potential is received, a specific channel opens allowing cations to flow in. What is this cation?

1. Na+
2. K+
3. Ca²⁺
4. Mg+

Answer 20

3. Ca²⁺

Question 21

The active zone is the site where neurotransmitters are released at the pre-synapse. Ca2+ is released and causes a conformation change in 2 proteins that are important for vesicles to fuse with the pre-synaptic membrane and release their neurotransmitters into the synaptic cleft. What are these 2 proteins called?

1. snaps and snappers
2. snappers and snares
3. snares and cyndricals
4. snares and snaps

Answer 21

4. snares and snaps

Question 22

Once a neurotransmitter has been released into the synaptic cleft, it will need to be removed once the action potential has finished. Which glial cell is able to take up the neurotransmitters and recycle them?

1. astrocytes
2. oligodendrocytes
3. microglia
4. gliomas

Answer 22

1. astrocytes
   - uptake, enzyme degradation and recycled back into pre synapse

Question 23

Once a neurotransmitter has been released into the synaptic cleft, it will need to be removed once the action potential has finished. If it is not recycled by astrocytes or at the pre-synapse, what can happen to it?

Answer 23

• degraded in the synaptic cleft to make it inactive
• example, is acetylcholinesterase in the image

Question 24

Once a neurotransmitter has been released into the synaptic cleft, it will need to be removed once the action potential has finished. What are the 2 approaches that can be used to recycle the neurotransmitter by the pre synapse?

Answer 24

1 - endocytosis and repackaged into vesicles

2 - endocytosis and degraded and made inactive

Question 25

What is a motor end plate?

Answer 25

- site where the pre-synapse meets a muscle at the neuromuscular junction

Question 26

At the axon terminal of a neuromuscular junction, do Schwann cells completely encompass the axon terminals?

Answer 26

- no - protects the nerve from the fluid surrounding the neuromuscular junction

Question 27

At the neuromuscular junctions the synaptic cleft is not flat, which is the case in nerve pre to post synapse. Instead it has grooves that resemble the crypts in the GI tract, called subjunctional folds/subneural clefts. What is the purpose of this?

Answer 27

- increase surface area for neurotransmitter action - increases the chance of an action potential

Question 28

In the image below, what is the dense bar also referred to as? 1. active zone 2. synaptic cleft 3. synaptic membrane 4. snaps zone

Answer 28

1. active zone * where neurotransmitters are released from pre-synapse

Question 29

From one action potential, roughly how many vesicles are likely to bind with the pre synapse and release neurotransmitters at a neuromuscular junction?

Answer 29

- _\>_ 125

Question 30

Acetylcholine (ACh) is able to bind with [_ionotropic_](https://en.wikipedia.org/wiki/Ionotropic_receptor) receptors on the post-synapse. These are Na+ channels that are present at the neuromuscular junction. The receptors are composed of 2 alpha, 1 gamma, 1 beta and delta subunit. What 2 subunits of the ACh receptor does ACh bind with? 1. one alpha and one beta 2. both alpha 3. alpha and gamma 4. gamma and beta

Answer 30

2. both alpha

Question 31

Acetylcholine (ACh) binds with sodium channels that are present at the neuromuscular junction. ACh binds with 2 alpha subunits on the Na+ channels, but is it only Na+ that can pass through these channels?

Answer 31

- no - K⁺ and Ca²⁺ can also pass, but mainly Na⁺

Question 32

At the neuromuscular junction, once an action potential has been received, ACh has been released and binds at the post synaptic cleft causing depolarisartion. There is a graded potential which causes the Na+ channels to open increasing the action potential, which leads to a muscle contraction. What is this called? 1. post-synaptic action potential 2. post-synaptic excitatory potential 3. end plate potential 4. active zone potential

Answer 32

3. end plate potential

Question 33

Synapses can be either chemical or electrical. Which type is faster? Why is the slower type better?

Answer 33

Electrical synapses are faster but chemical synapses allow for greater biological flexibility and therefore may be better in this regard.

Question 34

Gap junctions that form electrical synapses are made from how many subunits? What are these called?

Answer 34

Six connexin subunits form the channel and this is known as a connexon.

Question 35

Electrical synapses are bidirectional. What does this mean?

Answer 35

Gap junctions allow for the movement of ions in both directions.

Question 36

In electrical synapses the post-synaptic potentials are of a low amplitude and may not generate an AP in the post-synaptic cell so how does this occur?

Answer 36

Many low amplitude PSPs are integrated which when added together will cause an AP if the threshold is reached. Integration is required to determine if there is an AP.

Question 37

In nanometres roughly how large is the synaptic cleft?

Answer 37

30nm (0.00003mm)

Question 38

What is the active zone of a synapse?

Answer 38

Site of neurotransmitter release.

Question 39

Label A , B & C

Answer 39

a) Axodendritic synapse b) Axosomatic synapse c) axoaxonic synapse

Question 40

What is a Neurotransmitter?

Answer 40

These are molecules that cross the synaptic cleft and bind to receptor targets on the postsynaptic membrane. They are: • Synthesised in a neuron • Concentrated in the presynaptic termini • Acts on specific targets on the postsynaptic cell • If administered exogenously then it mimics the action of endogenously released ligand • Removed from the synaptic cleft to prevent constant stimulation

Question 41

Neurotransmitters are usually small molecules but they can also be...

Answer 41

Small peptides.

Question 42

Where are Neurotransmitters synthesised and how are they moved from one end of the neuron to the other?

Answer 42

Neurotransmitters are synthesised in the soma and vesicles carry them to the axon terminus. The vesicles are moved by microtubules. This is called axonal transport. The protein kinesin helps move the protein anterograde (towards the axon terminus) and dynein helps move the NTs retrograde (towards the soma).

Question 43

Define biological flexibility in terms of the events at the synapse...

Answer 43

Biological flexibility refers to the ability of other neurons to modulate each other.

Question 44

How do we molecular map chemical synapses?

Answer 44

Using biomarkers that allow us to image animal brains using fluorescent markers and in humans the most common way is via PET scanning.

Question 45

What is the job of snap and snare proteins?

Answer 45

They hold docked vesicles containing NT at the active zone and aid in exocytosis when the Ca2+ concentration increases.

Question 46

Label

Answer 46

1) Neurotransmitter in vesicle 2) Docking 3) Priming 4) Priming 5) Influx of Ca2+ 6) Exocytosis 6) Endocytosis 7) Recycling

Question 47

Neurotransmitters must be cleared from the synaptic cleft to prevent over activation of ion channels on the post-synaptic membrane. There are four main ways in which this is done - what are they?

Answer 47

1. Enzymic degradation in the synaptic cleft 2. Uptake into glial cells (with subsequent enzymic degradation) 3. Absorption into the presynaptic cell for repackaging 4. Absorption into the presynaptic cell for degradation

Question 48

The axon at the neuromuscular junction is myelinated except for the last bit - what occurs here?

Answer 48

On the final part of the axon near the skeletal muscle fibres there is partial myelination where a Schwann cell rests on top of the axon but does not wrap around it protecting it from the fluid in this area without fully myelinating the axon.

Question 49

Why does the neuromuscular junction have subjunction folds?

Answer 49

They increase the surface area for the neurotransmitter to be released.

Question 50

Why does the neuromuscular junction have subneural clefts?

Answer 50

These are present on the post-synaptic membrane and increase the surface area on which the neurotransmitter can act.

Question 51

There are approximately 300000 synaptic vesicles containing ACh at the neuromuscular junction. From one action potential roughly how many of these are released?

Answer 51

125

Question 52

What is the Dense Bar?

Answer 52

Essentially this is the active zone but present in the neuromuscular junction specifically. It is filled proteins and is the site at which the vesicles dock.

Question 53

The ACh receptor is composed of five identical units, two alpha, one beta, gamma and delta. To which subunit does ACh bind? What ions pass through this receptor?

Answer 53

ACh binds to the alpha subunits. This receptor principally allows the movement of Na+ ions but can also allow K+ and Ca2+.

Question 54

What is it that causes the end plate potential at the neuromuscular junction?

Answer 54

The influx of Na+ via the ACh receptors results in local depolarisation called end plate potential. Following this remaining Na+ channels open which results in muscle fibre contraction.