Gap which separates axon of one neurone from the dendrite of next neurone - approx 20-30nm
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What is the presynaptic neurone?
Neurone along which the impulse has arrived on
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What is the postsynaptic neurone?
Neurone that recieves the neurotransmitter
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What is the synaptic knob?
Swollen end of presynaptic which contains many mt & E.R. to enable it produce nt
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What are synaptic vesicles?
They contain nt which fuses with the presynaptic membrane to release the nt's into the cleft
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What are neurotransmitter receptors?
Receptor molecules which the nt's bind to in the postsynpatic membrane
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What are the two types of neurotransmitters?
1) Excitatory 2) Inhibitory
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What do excitatory neurontransmitters do?
Result in the depolarisation of the postsynaptic neurone. If threshold value is reached in postsy mem an action potential is triggered. Acetylcholine (ACh)
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What do inhibitory neurotransmitters do?
Result in the hyperpolarisation of postsy mem. Prevents action potential being triggered. Gamma-aminobutyric acid (GABA) is an example and is found in some synapses in the brain
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Transmission of impulses across synapse: 1
Act. pot. reaches end of presy neurone - depo. of presy mem = Ca2+ channels open & Ca2+ diffuse into presy knob - influx causes syn vesicles to move & fuse with presy mem & release nt into cleft via exocytosis
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Transmission of impulse across synapse: 2
The nt diffuses across the cleft & binds with specific receptor molecules on postsy mem - causes Na+ channels to open & Na+ diffuse into postsy neurone - triggers act. pot. & impulse is propagated along postsy neurone
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Why does the neurontransmitter have to be removed from the cleft after it has triggered an action potential?
So the stimulus is not maintained and another stimulus can arrive and affect the synapse
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How is actylcholine removed?
ACh is broken down by the enzyme called acetylcholinesterase into acetyl (ethanoic acid) and choline, which are taken back into the synaptic knob to be recycled
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What is a cholinergic synapse?
A synapse that uses the neurotransmitter acetylcholine (ACh)
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Where are cholinergic synpases found in the body?
Are common in the CNS in vertebates & at neuromuscular junctions
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Transmission across a cholinergic synapse: 1
Arrival of act. pot. at presy = Ca2+ channels to open & Ca2+ enter knob - Ca2+ influx into presy = syn vesicles fuse with mem & release ACh into cleft - ACh mols fuse with rec. sites on Na+ channel in postsy mem = Na+ channels open
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Transmission across a cholinergic synapse: 2
Na+ diffuse in rapidly along conc grad = generates new act. pot. in postsy - Acetylcholinesterase hydrolyses ACh -> choline & ehtanoic acid which diffuse back across cleft into presy to recycle & reforme into ACh by ATP - Na+ channels close
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What are the role of synapses?
Ensures impulses are unidirecitonal - Allow an impulse from one neurone be transmitted to a no. of neurones at multiple synapses - No. of neurone's may feed into same synapse w/ single postsy neurone = stimuli from different rec's interact = 1 result
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What is summation?
Build up of neurotransmitter in a synapse to sufficient levels to trigger an action potential
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What is spatial summation?
When no. of presy n's connect to 1 postsy n, each release nt which builds up to high enough level in sy to trigger act. pot. in the single postsy neurone
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What is temporal summation?
When 1 presy neurone release nt as result of act. pot. several times over short period. Builds up in sy until quantity is sufficient to trigger act. pot.
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Other cards in this set
Card 2
Front
How are nerve impulses transmitted across a synapse?
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