Synaptic transmission

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  • Created by: Hindleyc
  • Created on: 10-04-19 10:46
What is a synapse
Junction between 1 neurone and another
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What can a synapse do
pass signals onwards or they can block signals
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eg
traffic police controlling the pathways that nerve impulses travel along
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What might synapses between neurones do
direct an impulse to just one neurone or spread it out to several
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What is another type of synapse , similar in function but with a different structure
occur at junctions between motor neurones and muscle fibre where they are called neuromuscular junction
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As well as controlling deliberate movement like picking up an object what are synapses just as important in
regulating involuntary movement such as heart beat
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What is movement of this sort
Under the control of the autonomic nervous system
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What don't cells do at a synapse
join
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What is there
A physical gap 20nm between 1 neurone and another
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What is this called
synaptic cleft that occurs between the fine branches at the end of an axon and dendrites or cell body of the next neurone
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What is there a large number of and what does this provide
Synapses (billions), large surface area for this transfer of information
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eg
Over 1000 synapses may be found on dendrites and cell body of 1 motor neurone in the spinal cord
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What do synapse consist of
swelling at the end of a nerve fibre called a synaptic knob
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How do impulses cross this gap
As chemical transmitters
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Why is there a gap
not in direct contact with each other
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Why is it chemical
Potential difference can't cross from 1 neurone to other so electrical to chemical
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Steps
Presynaptic neurone, synaptic cleft(gap), post synaptic neurones
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What does the cytoplasm of synaptic knob have
large number of mitochondria
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What is stored in it
transmitters in tiny bags of membrane called synaptic vesicles
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What is the membrane of the synaptic knob nearest the synapse called
presynaptic membrane
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What is the membrane of the dendrite called
Postsynaptic membrane
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6 main stages of transmission of the impulse across the gap
Action potential arrives at the end of the presynaptic neurone , This action potential causes calcium gated channels in the membrane to open resulting in an influx of Ca ions,
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Then
Calcium ions cause the synaptic vesicles to move towards the presynaptic membrane fuse with it and release the transmitter substance into the synaptic cleft(acetyl choline), Transmitter substance diffuses across the cleft to the post S-M
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then
Transmitter molecules bind to protein molecules on the post synaptic membrane, Na+ channels on post synaptic membrane open causing na+ to move into the cell causing it to depolarise (depolarisation of PSM) starting new impulse in PostSM-AP generated
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What can the different ways in synapses connect neurones to others or to muscles can be used to
produce a range of responses
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What can transmitters have
Either an excitatory (increase the activity of the next cell) or inhibitory effect (decrease the activity of the next cell)
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What does it depend on
the properties of the receptor site
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What does this enable synapses
to either pass of signals or to block them
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If effect is inhibitory what does this mean
That hyperopolaraisation of the postsynaptic membrane occurs and the inside becomes more -ve and therefore even less likely to set up a nerve impulse
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Why does this happen
Because transmitter increases the permeability to postsynaptic membrane to Cl- ions (rush in) and K+ to rush out
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What. does this make
Potential difference -90mv so neurone less likely to trigger an action potential (more -ve)
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What is there a delay of
around 1/2 Ms while an impulse crosses a synapse (time needed for the transmitter to diffuse from the pre synaptic membrane across the gap, bind to a receptor protein on the post synaptic membrane and activate or inhibit the next cell)
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What does the arrival of acetyl choline neurotransmitter cause
Change in the shape of the receptor site which results in ion channels opening up in post synaptic membrane
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What then
Entry of Na+ through post synaptic membrane causes depolarisation of the membrane which excites the cell making it more likely to set up a nerve impulse (AP)
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What are quickly removed from the synapses
Transmitters after they have produced the change in the permeability of the post synaptic membrane
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What if they were not
Neurones would keep on firing impulses uncontrolablly
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What happens then
Broken down by enzyme into acetyl and chloline in cleft
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What is this why
Mitochondria are needed as requires ATP for the 3 R's
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What are the 3 R's
Reabsorb A+C, Resynthesise AC, Repackage- into pre ready for next AP arrival
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What is this principle
Same whatever the NT but different enzyme
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What can synapses become
tired
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When does this happen
When so many AP arrive in so short a time that the cell runs out of transmitter substance
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What can the impulse no longer do
Cross the synapse
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What is this loss of response at a synapse called
Adaptation
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What does this mean, why
Animals ignore stimuli that go on for a long Time eg clothes bc these stimuli irrelevant to our survival but sudden changes in the environment are more important to our survival eg car
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As the transmitter is removed almost as quickly as it is released what might be needed to produce enough transmitter to trigger the next cell
Several AP needed in quick succession
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What is temoral summation
Rapid release of transmitter from the same synaptic knob and their effects added together give rise to an AP
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Also known as
Summation through time
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What is spacial summation
The transmitter from 2 or more neurones acting side by side- feeding same next neurone- adding together
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What are they related through
Space at same time
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Therefore how can impulses be set up in a post synaptic neurone
By either weak stimulation by several pre synaptic neurone or repeated stimulation by 1 pre synaptic neurone
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What can some NT cause
CL- ion channel to open in the post s N making it less likely that an AP will fire as the neurone becomes hyper polarised
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What are these types of transmitters
Inhibitory
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Why do synapses have property of uni-directionality
Since NT is only released from the Pre S M and receptors for NT are only found on the Post S M- only one release and only 1 detect NT
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In temporal what does NT do
Stay in cleft
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What does temporal do
Stop it getting overloaded- AP not always fired respond when stimulus needs to be responded to
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What may the neurones do
Synapse with 100s/1000s of other neurones
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What is summation important for
Healthy brain functioning- ignore weak stimulus but stronger stimulus may cause injury so requires response
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What does a strong stimulus (Change in environment) send
A high freq of nerve impulses to the brain
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When temporal summation has released enough neurotransmitters to cross the synapse what happens
The brain registers pain and brings about avoiding action
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eg spatial
deer drinking needs all 3 conditions met so could be controlled by 3 neurones and when all fire together enough transmitter builds up to fire drinking neurone
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Other cards in this set

Card 2

Front

What can a synapse do

Back

pass signals onwards or they can block signals

Card 3

Front

eg

Back

Preview of the front of card 3

Card 4

Front

What might synapses between neurones do

Back

Preview of the front of card 4

Card 5

Front

What is another type of synapse , similar in function but with a different structure

Back

Preview of the front of card 5
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