Lecture 5: Synaptic Transmissions | (General Features)

Question 1

What are the two different types of synapses?

Answer 1

• electrical synapse (gap junction)

- chemical synapse

Question 2

Describe an electrical synapse

Answer 2

it is the junction between cells, the holes/pores between neighbouring cells

Question 3

What are gap junctions/electrical synapses made of?

Answer 3

specialised proteins in the membrane which make pores by linking onto the proteins of the neighbouring cell’s gap junction

Question 4

What is the communication via a gap junction? How fast is this?

Answer 4

it is the flow of ions from cell to cell to transmit and this is very fast

Question 5

Briefly describe a chemical synapse

Answer 5

synaptic vesicles fuse to the membrane which the AP arrives which releases the neurotransmitter across the synaptic cleft to the post synaptic cell

Question 6

what are five key features of the chemical synapse?

• it is _______ than the electrical synapse
• it relies on a _________ crossing the _______ _______
• it is a complex series of _________
• the _________ is packaged in _________
• the __________ strength can be ________

Answer 6

• it is slower than the electrical synapse
• it relies on a chemical crossing the synaptic cleft
• it is a complex series of events
• the neurotransmitter is packages in vesicles
• the synapse strength can be modified

Question 7

Are gap junctions always open?

Answer 7

no

Question 8

Do gap junctions spend more time open or closed?

Answer 8

closed

Question 9

What four things can open the gap junctions?

Answer 9

• voltage
• pH
• Ca2+
• receptors

Question 10

What happens to the electrical synapses when the pre synaptic cell becomes depolarised?

Answer 10

there is a conformational change to open the pore so the depolarisation can be passed on

Question 11

What are the three types of neurotransmission?

Answer 11

• classical neurotransmission
• gaseous neurotransmission
• neuropeptide neurotransmission

Question 12

What type of neurotransmitter is associated with classical neurotransmission?

Answer 12

small-molecule neurotransmission

Question 13

What types of molecule is associated with neuropeptide neurotransmission?

Answer 13

neuropeptides

Question 14

What type of molecule is associated with gaseous neurotransmission?

Answer 14

gasses

Question 15

Describe the process of classical neurotransmission

Answer 15

• vesicle transporter concentrates neurotransmitter into vesicles
• the small molecule neurotransmitters diffuse across the synaptic cleft and bind to post-synaptic receptors

Question 16

Describe the process of neuropeptide neurotransmission

Answer 16

• neuropeptides released into the synaptic cleft to bind to synaptic receptors and/or
• peptides diffuse in the extracellular space and bind to non-synaptic receptors

Question 17

Describe the process of gaseous neurotransmission

Answer 17

• these do not get released at the synapse, instead (eg.) NO is released which acts as a neurotransmitter to diffuse out of the cell of origin and directly into other cells
• they can act inside the cell of origin or in the cells distant from the point of release

Question 18

Can the same neuron release both small molecule neurotransmitter and neuropeptides?

Answer 18

yes, this is very common in the central nervous system (although they could be serving slightly different functions)

Question 19

How does gaseous transmission take effect?

Answer 19

it interacts with second messenger pathways (intracellular machinery) in the post-synaptic cell, rather than through receptor interactions that the small molecule and neuropeptides work

Question 20

If there is a high concentration of gaseous neurotransmitters, would they diffuse further than if there was a low concentration of neurotransmitter?

Answer 20

yes

Question 21

Where do the neurotransmitters go that were inside vesicles?

Answer 21

don’t get inside the post-synaptic cell and the things that are not in the vesicles just diffuse across and do get inside the post-synaptic cell

Question 22

What happens after exocytosis has occurred?

Answer 22

re-uptaken and refilled

Question 23

What are the two different types of neurotransmitter exocytosis and recycling?

Answer 23

• fusion and collapse (full fusion)

- kiss and run (partial fusion)

Question 24

What is competence maturation?

Answer 24

the vesicles are getting prepared

Question 25

Where are the vesicles located in the presynaptic cell?

Answer 25

some vesicles are sitting by the surface, ready to be released (right near where they need to fuse to the membrane) and some are further up by the axon terminal so have to physically move to the surface before they can fuse with the membrane

Question 26

Describe the exocytosis part of classical (full) fusion

Answer 26

the vesicles fuse to the membrane and flattens out to become part of the membrane so that everything inside the vesicle gets spilled out into the extracellular space

Question 27

Describe the recycling part of the classical (full) fusion

Answer 27

a protein called clathrin which marks that bit of the membrane as “special” and this helps machinery inside the cell fold that bit of membrane back into vesicle shape to be retaken up into the presynaptic terminal and filled with more neurotransmitter. It then hangs out in the reserve pool and then makes it’s way down closer to the surface (readily releasable pool)

Question 28

Describe the exocytosis part of partial fusion

Answer 28

the vesicle fuses to the membrane surface, opens a whole but doesn’t flatten out like another bit of the membrane - it stays like a vesicle stuck to the inside of the membrane

Question 29

Is is more difficult for the contents of the vesicle to get out in full or partial fusion? Therefore, which method delivers less neurotransmitter into the synaptic cleft?

Answer 29

partial fusion (especially if this is a neuropeptide)

Question 30

Describe the recycling part of the partial fusion

Answer 30

The vesicle comes off the membrane and back into the pool. It is unsure whether it goes into the reserve pool or hangs about near the surface of the membrane in the readily releasable pool (because these are likely to still have a little bit of neurotransmitter in them) but likely to be in readily releasable pool

Question 31

What is the first in the sequence of events during classical chemical neurotransmission?

Answer 31

an action potential is propagated down the axon, to the presynaptic terminal

Question 32

In the sequence of events during classical chemical neurotransmission, what occurs after an action potential is propagated down the axon to the presynaptic terminal? What number is this in the sequence of events?

Answer 32

the presynaptic terminal is depolarised and voltage-gated Ca2+ channels open
this is the second thing in the sequence

Question 33

In the sequence of events during classical chemical neurotransmission, what occurs after the presynaptic terminal is depolarised and the voltage-gated Ca+ channels open? What number is this in the sequence of events?

Answer 33

the Ca2+ ions trigger vesicle fusion with the presynaptic membrane
this is the third thing in the sequence

Question 34

In the sequence of events during classical chemical neurotransmission, what occurs after the Ca2+ ions trigger vesicle fusion with the presynaptic membrane? What number is this in the sequence of events?

Answer 34

the neurotransmitter is released into the synaptic cleft, the vesicle is recycled (kiss and run) usually happens within one second
this is the fourth thing in the sequence

Question 35

In the sequence of events during classical chemical neurotransmission, what occurs after the neurotransmitter is released into the synaptic cleft and the vesicles are recycled? What number is this in the series of events?

Answer 35

the neurotransmitter diffuses within the synaptic cleft

this is the fifth thing in the sequence

Question 36

In the sequence of events during classical chemical neurotransmission, what occurs after the neurotransmitter diffuses within the synaptic cleft? What number is this in the series of events?

Answer 36

the neurotransmitter binds to its specific receptors on the postsynaptic membrane
this is the sixth thing in the sequence

Question 37

In the sequence of events during classical chemical neurotransmission, what occurs after the neurotransmitter binds to its specific receptor on the postsynaptic membrane? What number is this in the series of events?

Answer 37

1. Glutamate opens the Na+ channels on the postsynaptic cells which causes a local postsynaptic cell depolarisation (the excitatory post-synaptic potential: EPSP)

or

2. GABA opens the K+ or Cl- channels on the post-synaptic cells which causes a local postsynaptic cell hyperpolarisation (the inhibitory post synaptic potential: IPSP)

this is the seventh thing in the sequence

Question 38

In the sequence of events during classical chemical neurotransmission, what occurs after the EPSP or IPSP? What number is this in the series of events?

Answer 38

the neurotransmitter is degraded or taken up (by glia or the presynaptic terminal)
this is the eighth thing in the sequence

Question 39

In the sequence of events during classical chemical neurotransmission, what occurs after the neurotransmitter is degraded or taken up? What number is this in the series of events?

Answer 39

recycling and refilling of the vesicles (clathrin-mediated) in roughly 20 seconds
This is the ninth (last) thing to occur in the sequence

Question 40

Electrical synapses are faster than chemical synapses BECAUSE electrical synapses conduct ions directly from cell to cell but chemical synapses release neurotransmitters to activate postsynaptic receptors

Answer 40

both of these statements are true and the second causes the first

Question 41

Define temporal summation

Answer 41

summation between EPSPs from the same input (synapse) that occur close enough in time

Question 42

Define spatial summation

Answer 42

summation between events that occur close together in space from different inputs (this still requires them to be close in time)

Question 43

What is synaptic modulation?

Answer 43

insertion of new proteins into the post-synapse (insertion of more receptors)

Question 44

How long down synaptic modulation last?

Answer 44

hours to days to even months or years