Lecture 5: Synaptic Transmissions | (General Features) Flashcards
What are the two different types of synapses?
- electrical synapse (gap junction)
- chemical synapse
Describe an electrical synapse
it is the junction between cells, the holes/pores between neighbouring cells
What are gap junctions/electrical synapses made of?
specialised proteins in the membrane which make pores by linking onto the proteins of the neighbouring cell’s gap junction
What is the communication via a gap junction? How fast is this?
it is the flow of ions from cell to cell to transmit and this is very fast
Briefly describe a chemical synapse
synaptic vesicles fuse to the membrane which the AP arrives which releases the neurotransmitter across the synaptic cleft to the post synaptic cell
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 ________
- 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
Are gap junctions always open?
no
Do gap junctions spend more time open or closed?
closed
What four things can open the gap junctions?
- voltage
- pH
- Ca2+
- receptors
What happens to the electrical synapses when the pre synaptic cell becomes depolarised?
there is a conformational change to open the pore so the depolarisation can be passed on
What are the three types of neurotransmission?
- classical neurotransmission
- gaseous neurotransmission
- neuropeptide neurotransmission
What type of neurotransmitter is associated with classical neurotransmission?
small-molecule neurotransmission
What types of molecule is associated with neuropeptide neurotransmission?
neuropeptides
What type of molecule is associated with gaseous neurotransmission?
gasses
Describe the process of classical neurotransmission
- vesicle transporter concentrates neurotransmitter into vesicles
- the small molecule neurotransmitters diffuse across the synaptic cleft and bind to post-synaptic receptors
Describe the process of neuropeptide neurotransmission
- 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
Describe the process of gaseous neurotransmission
- 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
Can the same neuron release both small molecule neurotransmitter and neuropeptides?
yes, this is very common in the central nervous system (although they could be serving slightly different functions)
How does gaseous transmission take effect?
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
If there is a high concentration of gaseous neurotransmitters, would they diffuse further than if there was a low concentration of neurotransmitter?
yes
Where do the neurotransmitters go that were inside vesicles?
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
What happens after exocytosis has occurred?
re-uptaken and refilled
What are the two different types of neurotransmitter exocytosis and recycling?
- fusion and collapse (full fusion)
- kiss and run (partial fusion)
What is competence maturation?
the vesicles are getting prepared
Where are the vesicles located in the presynaptic cell?
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
Describe the exocytosis part of classical (full) fusion
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
Describe the recycling part of the classical (full) fusion
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)
Describe the exocytosis part of partial fusion
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
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?
partial fusion (especially if this is a neuropeptide)
Describe the recycling part of the partial fusion
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
What is the first in the sequence of events during classical chemical neurotransmission?
an action potential is propagated down the axon, to the presynaptic terminal
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?
the presynaptic terminal is depolarised and voltage-gated Ca2+ channels open
this is the second thing in the sequence
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?
the Ca2+ ions trigger vesicle fusion with the presynaptic membrane
this is the third thing in the sequence
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?
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
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?
the neurotransmitter diffuses within the synaptic cleft
this is the fifth thing in the sequence
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?
the neurotransmitter binds to its specific receptors on the postsynaptic membrane
this is the sixth thing in the sequence
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?
- Glutamate opens the Na+ channels on the postsynaptic cells which causes a local postsynaptic cell depolarisation (the excitatory post-synaptic potential: EPSP)
or
- 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
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?
the neurotransmitter is degraded or taken up (by glia or the presynaptic terminal)
this is the eighth thing in the sequence
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?
recycling and refilling of the vesicles (clathrin-mediated) in roughly 20 seconds
This is the ninth (last) thing to occur in the sequence
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
both of these statements are true and the second causes the first
Define temporal summation
summation between EPSPs from the same input (synapse) that occur close enough in time
Define spatial summation
summation between events that occur close together in space from different inputs (this still requires them to be close in time)
What is synaptic modulation?
insertion of new proteins into the post-synapse (insertion of more receptors)
How long down synaptic modulation last?
hours to days to even months or years
