Synapses (4.1.2)

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What size is the synapse?
About 20nm wide.
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What crosses a synapse?
Neurotransmitters are released from the pre-synaptic membrane and diffuse across the synapse. It triggers Na+ ions to enter the post-synaptic membrane, this starts another action potential.
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What are cholinergenic synapses?
Synapses that use acetylcholine as their transmitter substance.
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Describe the specialised features of the pre-synaptic knob?
Many mitochondria, for ATP. Large amount of smooth ER. Vesicles of acetylcholine, which will diffuse across. Voltage-gated Ca+ channels in the membrane.
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Describe the structure of the post-synaptic membrane.
Contains special Na+ channels that respond to acetylcholine. These channels consist of 5 polypeptides, two of these make up the receptor site.
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Summarise the transmission of an action potential across a synapse.
A.P arrives at synaptic knob. V-gated Ca2+ channels open- Ca2+ diffuses into pre-synaptic memb. Ach vesicles fuse with memb., contents released- exocytosis. Ach diffuses across synapse to post-synaptic memb. Attaches to receptors, Na+ channels open.
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How does the action potential continue after a synapse?
Once the Ach attaches to receptors, the Na+ channels open and Na+ diffuses in, triggering an action potential.
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What is acetylcholine broken down into?
Ethanol and choline, using the acetylcholinesterase enzyme.
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Why is it important to break down acetylcholine?
To prevent continuous transmission of action potentials in next neurone.
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Why does the cytoplasm of the synaptic knob contain lots of mitochondria?
Aerobic respiration happens here and releases ATP energy which is needed to repackage the neurotransmitter.
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Why does the cytoplasm of the synaptic knob contain lots of smooth ER?
Used to make lipids. Needed to make the membranes around the vesicles to repackage neurotransmitter.
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What is a neuromuscular junction?
Where the end of a motor neurone reaches a muscle. The plasma membrane of the muscle fibre is the post-synaptic membrane.
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Give 3 uses of synapses.
There can be many pre-synaptic neurones at one synapse- leading to a coordinated response. Synapses ensure the action potential is transmitted in one direction. They help to filter out low-level stimuli.
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Give 2 more uses of synapses.
Prevent repeated stimulation of the nervous system- once neurotransmitter released, takes time to be repackaged. Several neurones meeting at a synapse can cause summation to amplify stimulus.
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What is temporal summation?
Action potentials separated by time. A.P occur close together and collectively cause a response.
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What is spatial summation?
Action potentials from different regions. Several neurones meet at one synapse and collectively cause a response.
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Card 2

Front

What crosses a synapse?

Back

Neurotransmitters are released from the pre-synaptic membrane and diffuse across the synapse. It triggers Na+ ions to enter the post-synaptic membrane, this starts another action potential.

Card 3

Front

What are cholinergenic synapses?

Back

Preview of the front of card 3

Card 4

Front

Describe the specialised features of the pre-synaptic knob?

Back

Preview of the front of card 4

Card 5

Front

Describe the structure of the post-synaptic membrane.

Back

Preview of the front of card 5
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