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Summary Notes on Synaptic Transmission - AQA A Level Biology
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Synaptic transmission- Nervous impulse arrives in presynaptic neuron and depolarises membrane
- Voltage gated calcium ion channels open
- Ca2+ ions move into presynaptic knob by facilitated diffusion
- Causes vesicles containing Ach to move and fuse with presynaptic neuron
- Ach is released into synaptic clef by exocytosis
- Ach diffuses across synaptic cleft and binds to receptor sites on ligand-gated sodium ion
channels on postsynaptic membrane
- Na+ enter the post synaptic neuron by facilitated diffusion causing depolarisation
- Depolarisation ends as Ach is broken down into acetate and choline by acetylcholinesterase
- Synaptic knob reabsorbs choline from synaptic clef and use it to synthesise new molecules of
Ach
- If the depolarisation is above threshold then a new action potential is produced
Exocytosis
- Where vesicles move and fuse to membrane of post synaptic neurone
Synapse
- Gap between neurones that allows connections to be formed between neurones
Electrical impulses cannot cross the gap, so they have to be converted to chemical energy, then back
into electrical energy again
Features of the cholinergic synapse:
- Info travels across cholinergic synapses by a way of neurotransmitter called acetylcholine
- Neurotransmitter is synthesised and stored in vesicles in the enlarged ends of the axon
terminals called synaptic knobs
- Synaptic knobs contain many mitochondria to generate ATP for synthesis of
neurotransmitter and large amount of endoplasmic reticulum
- Presynaptic membrane contains voltage-gated calcium ion channels
- Post-synaptic membrane contains receptors which are associated with sodium ion channels
- Synaptic cleft contains an enzyme called acetylcholinesterase which breaks down the
neurotransmitter (acetylcholine)
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