15.5- Structure and function of synapses

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What is a synapse?
The point where one neurone communicates with another or with an effector
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How do synapses transmit information?
By chemicals called neurotransmitters
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Name two types of neurotransmitter
- Acetylcholine - Noradrenaline
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What is the synaptic cleft?
The small gap separating neurones
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What is the name of the neurone which releases the neurotransmitter?
Presynaptic neurone
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What protein is present on the presynaptic membrane?
Calcium ion protein channels
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What is the neurone at the other side of the synapse called?
Postsynaptic neurone
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What protein is present on the postsynaptic membrane?
sodium ion protein channels
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What is the synaptic knob?
The swollen portion at the end of an axon at the synapse
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What two organelles in the synaptic knob contribute to the manufacure of the neurotransmitter?
Mitochondria and endoplasmic reticulum
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Where is the neurotransmitter stored in the synaptic knob?
Inside synaptic vesicles
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How are neurones unidirectional?
The nerve impulse and neurotransmitter via the synapse travel in one direction only- from the presynaptic neurone to the postsynaptic neurone
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What three features ensures unidirectionality?
- Synaptic vesicles containing neurotransmitter only produced in presynaptic neurone - Receptor proteins for neurotransmitter only in postsynaptic neurone - Channel proteins for Na+ ions only on postsynaptic membrane
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Why is summation sometimes necessary?
As low-frequency action potentials often lead to the release of insufficient concentrations of neurotransmitter to trigger a new action potential in the postsynaptic neurone, but summation can enable this action potential to be created
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What are the two types of summation?
- Spatial summation - Temporal summation
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What is spatial summation?
In which a number of different presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the postsynaptic neurone to trigger a new action potential
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What is temporal summation?
In which a single presnaptic neurone releases neurotransmitter many times over a very short period to exceed the concentration of the threshold value of the postsynaptic neurone to trigger a new action potential
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What do inhbitory synapses do?
They make it less likely that a new action potential will be created on the postsynaptic neurone
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Describe how an inhibitory synapse works
- The presynaptic neurone releases a neurotransmitter that binds to Cl- ion channels on the postsynaptic membrane - The channels open allowing Cl- ions into the postsynaptic neurone by facillitated diffusion - The neurotransmitter also causes K+ -->
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ion channels to open allowing K+ ions to move out of the postsynaptic neurone into the synapse - As Cl- ions diffuse in and K+ ions diffuse out of the postsynaptic neurone this makes it more negative inside than its normal resting potential; it -->
becomes hyperpolrised - It is less likely a new action potential will be created as a larger influx of sodium ions would be needed to depolarise the membrane to create an action potential
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How do synapses transmit information?

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By chemicals called neurotransmitters

Card 3

Front

Name two types of neurotransmitter

Back

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Card 4

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What is the synaptic cleft?

Back

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Card 5

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What is the name of the neurone which releases the neurotransmitter?

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