Nerve junctions

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  • Created by: Steff06
  • Created on: 19-05-16 17:10
What is a neurotransmitter?
A chemical that diffuses across the cleft of a synapse to transmit a signal to the postsynaptic neurone.
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What do cholingeric synapses use as their neurotransmitter?
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Describe the synaptic knob
A swelling at the end of the presynaptic membrane.
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What is the definition of a synapse?
A junction between 2 or more neurones.
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What is the gap in between 2 neurones called?
The synaptic cleft
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How does an action potential get from one neurone to another?
The presynaptic action potential causes the release of a chemical (transmitter) that diffuses across the gap and generates a new action potential in the postsynaptic neurone.
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Describe the specialised features of the synaptic knob (4)
Has many mitochondria as ATP is required, large amount of smooth endoplasmic reticulum, vesicles of acetylcholine and voltage-gated calcium channels in the membrane.
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What does the post synaptic membrane contain and what do these do?
Contains specialised sodium ion channels. These respond to the transmitter substance.
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How many polypeptide molecules do the channels consist of and which are specific to acetylcholine?
Channels consist of 5 polypeptides. 2 have a specific receptor site to acetylcholine. They have a complementary shape to acetylcholine and can bind into the site.
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What happens when acetylcholine binds to the 2 receptors?
The sodium ion channels open.
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Describe the transmission across the synapse from the presynaptic knob to calcium ions in the synaptic knob.
Action potential arrives at the synaptic knob. Voltage-gated calcium ion channels open. Calcium ions diffuse into the synaptic knob
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What happens after the calcium ions have diffused into the knob?
Calcium ions cause the synaptic vesicles to move to and fuse with the presynaptic membrane. Acetylcholine is released by exocytosis.
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What happens after acetylcholine choline is released?
Acetylcholine molecules diffuse across the cleft and bind to the receptor sites on the sodium ion channels in the postsynaptic membrane.
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What happens after the binding occurs?
Sodium ion channels open and sodium diffuses across the postsynaptic membrane into the postsynaptic neurone.
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What is then created?
A generator potential is created. If sufficient generator potentials combine, the potential across the postsynaptic membrane reaches the threshold potential. A new action potential is created.
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What happen after an action potential is created?
It will pass down the postsynaptic neurone.
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What is acetylcholinesterase and where is it found?
An enzyme found in the synaptic cleft.
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What is the function of aceetylcholinesterase?
To hydrolyse the acetylcholine into ethanoic acid and choline.
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What does this stop?
Stops the transmission of signals so that the synapse does not continue to produce action potentials in the postsynaptic neurone.
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What happens to the ethanoic acid and choline?
They are recycled. Re-enter the synpatic knob by diffusion and are recombined to acetylcholine using ATP from respiration in mitochondria.
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Where does this recycled acetylcholine go?
Is stored in synaptic vesicles for future use.
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Card 2


What do cholingeric synapses use as their neurotransmitter?



Card 3


Describe the synaptic knob


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Card 4


What is the definition of a synapse?


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Card 5


What is the gap in between 2 neurones called?


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