Synaptic transmission

• Synaptic transmission involves the release of neurotransmitters into the synaptic cleft, which diffuse across to the post-synaptic membrane and bind to specific receptors.
• Neurotransmitters can trigger an action potential, cause muscle contraction or cause a hormone to be secreted.
• Synapses make sure impulses are unidirectional- impulse can only travel in one direction.
• Neurotransmitters are removed from the cleft so the response doesn’t keep on happening- taken back into the presynaptic neurone or they are broken down by enzymes.
• Synapses that use acetylcholine are cholinergic synapses.
• An action potential arrives at the synaptic knob of the post-synaptic neurone.
• The action potential stimulates voltage gated calcium ion channels in the presynaptic neurone to open.
• Calcium ions diffuse into the synaptic knob.
• The fusion of the vesicles is triggered by the influx of calcium ions into the presynaptic knob, causing the synaptic vesicles to fuse with the presynaptic membrane and release Ach into the synaptic cleft by exocytosis.
• Ach diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane in the postsynaptic neurone to open.
• The influx of sodium ions into the post-synaptic membrane causes depolarisation.
• An action potential on the post-synaptic membrane is generated if threshold is met and Ach is removed from the synaptic cleft so the response doesn’t keep happening.
• Ach is broken down in the synaptic cleft by AchE and the products are re-absorbed by the post-synaptic neurone to make more Ach.
• Neuromuscular junction is a specialised cholinergic synapse between a motor neurone and a muscle cell, where Ach binds to cholinergic receptors called nicotinic cholinergic receptors.
• Neuromuscular junction has folds in the post-synaptic membrane that form clefts, where AchE is stored.
• The postsynaptic membrane has more receptors than other synapses, making it always excitatory.
• When a motor neurone fires an action potential, it triggers a response in a muscle cell.
• This isn’t always the case for a synapse between two neurones.