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NTT Exam Questions & Answers 2024/2025 Synapses - ANSWERSFundamental aspect of all brain functionbecause they transmit information between neurons (and to muscle)• act as information filters based on theirindividual properties• one of these properties is the release probability, Pr - a...

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NTT Exam Questions & Answers
2024/2025

Synapses - ANSWERSFundamental aspect of all brain functionbecause they transmit information
between neurons (and to muscle)•



act as information filters based on theirindividual properties• one of these properties is the release
probability, Pr - average number of vesicles released per spike• can change their properties: both in the
short-term and long-term dysfunction and a target for many drugs



- short-term changes (depression,facilitation) act in seconds to alter how signals flow through circuits



- long-term changes (potentiation)are the basis for learning andmemory• are also major sites for sites
for nervous system



The basic picture of synaptic transmission - ANSWERSIt is the influx of Ca2+ down its concentration
gradient and triggered by depolarization that drives the transmission process.



The Vesicle Hypothesis - ANSWERSElectron Microscopy: Early electron microscopy studies provided the
first direct visual evidence of vesicles in nerve cells. Researchers observed small, membrane-enclosed
structures in nerve terminals, which were later confirmed to be synaptic vesicles involved in the release
of neurotransmitters.

Neurotransmitter Release: Experiments have demonstrated that when neurons are stimulated,
neurotransmitters are released into the synaptic cleft, the small gap between nerve cells. This release
occurs in a quantal fashion, supporting the idea that neurotransmitters are packaged into vesicles and
released in discrete amounts.



Vesicle Fusion: The process of vesicle fusion with the cell membrane, also known as exocytosis, has been
extensively studied. Researchers have identified specific proteins like SNARE proteins that mediate the
fusion process, providing molecular evidence of vesicle involvement in neurotransmitter release.



Pharmacological Studies: Various drugs and toxins, such as botulin

,How was Ca-sensitive molecule controlling fast neurotransmission identified? - ANSWERS·
Synaptotagmin

· Binds to 10's of micromolar concentrations of calcium (affinity)

· Is cooperative to 3 or 4 ions

· Could do a knockout test to find if it is responsible for fast transmission rather than just involved.

· Describe key experiment

· Voltage clamp

· In wildtype, a single simultaneous peak

· But in the knockout there were many small asynchronous peaks

o LOOK AT KEY EXPERIMENTS

· This also shows that there is a calcium independent pathway

· This component is slower and requires lower levels of calcium, as it will spill over in the initial release
before the late firing happens.

· This could be because the other calcium sensitive molecules may be further from the membrane

· Can talk about how to sensor acts - complexin



Depolarisation and ACh release - ANSWERSDepolarisation depletes vesicle population of nerve terminal -
which is seen to be reversible as 60 minutes after the end of stimulation, the vesicle pool at the terminal
has refilled.



Depolarisation then fast freezing: we can visualise fusion between vesicle and membrane. Depolarisation
makes fusion more frequent. The frequency in which the 'omega' shapes of fusing vesicles is seen
increases dramatically immediately after a stimulus is applied



Imaging vesicle fusion - ANSWERSThe 'slammer' is what's used in fast freezing. It drops the
neuromuscular junction from a plunger into liquid helium. Once the plunger is dropped theres a very
fixed delay between the stimulus and the freezing.



Freeze fracture: Splitting sample apart down a weak structural plane, one of these planes just happens
to be the synaptic junction. This allows visualisation of calcium channels at rest, then pits showing
exocytosis and the pits moving to the side showing endocytosis. these pits move to allow another AP to
transmit NT

,Reducing external [Ca 2+] conc - ANSWERSLeads to lowering the release probability, meaning most
stimuli would fail to evoke release.



An alternative approach to testing this is increasing the external conc of magnesium, which antagonises
the effect of calcium. Doing this demonstrates the quantal nature of vesicle release, as the amplitude
frequency histogram shows 4 peaks, each being multiples of eachother (EG: the fourth peak is 4x the size
of the first)



Role of calcium in ACh release - ANSWERSHow do we know Ca2+ entry is needed for transmitter release?



Here's the experiment:

Neuromuscular junction perfused with Ca2+-free solution



Recording in muscle fibre (postsynaptically)



Stimulus applied to nerve



Iontophoretic application of Ca2+ before or after stimulus



With no calcium present, no EPP is observed after depolarising stimulus applied



When Ca is applied just before the pulse we get an EPP



When calcium is applied just after the pulse, no EPP is observed



Therefore, Ca 2+ entry is necessary for ACh release and has to be applied before the pulse. It also must
be present DURING nerve depolarisation

So depolarisation-induced Ca 2+ entry is involved: This means voltage-gated Ca 2+ channels

, Evidence that Calcium influx is necessary for NT release - ANSWERSOne type:

Manipulate voltage-gated calcium channels in squid giant synapse on presynaptic and postsynaptic
neurons.



the neuron was voltage clamped and a 3ms depolarisation performed. In the control, it elicited an EPSP,
but when a Ca 2+ channel blocker was added, no EPSP was elicited.



Evidence that Calcium influx is sufficient for NT release - ANSWERSManipulate calcium INSIDE the
terminal.



Calcium buffers (such as EGTA or BAPTA) are small molecules that bind CA 2+ ions with high-affinity,
thereby preventing them from binding to proteins inside the cell. The internal Ca 2+ concentration is
measured with aequorin.



In the control, a presynaptic membrane potential was recorded, followed by a postsynaptic membrane
potential about 1ms later. When a calcium buffer was added, the presynaptic potential was recorded,
but no postsynaptic potential occurred.



Visualising calcium channels and calcium influx in the presynaptic terminal - ANSWERSusing toxins that
bind to different channels to visualise them. Example given was calcium ion channels in green and ACh
receptors in red - images were then superimposed. We cna then see rises in calcium concentration in
relation to positinos of these receptors



Calcium alone is sufficient for ACh release - ANSWERSSquid giant synapse



Nitrophen - "caged" Ca2+



Nitrophen releases Ca2+ in response to a UV flash



Response to nitrophen is an EPSP (excitatory post-synaptic potential)



Depolarisation is not essential for ACh release, Ca 2+ alone is enough.

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