the action potential & impulse/signal propagation learning objective be able to describe what a...
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The Action Potential & Impulse/Signal Propagation
Learning ObjectiveBe able to describe what a synapse is.
Be able to describe how an action potential causes the activation of synapses.
Be able to explain how signals cross the synapse.
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• A synapse is the point where neurons connect together.
• An action potential travels across an axon and arrives at the synapse.
• The synapse is the opposing membranes of two neurons separated by a gap.
• Because of this gap signals must be passed on chemically
A Synapse
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• The synapse is made of several parts.
• The Pre-Synaptic membrane is on the neurone where the signal is coming from.
• The Post-Synaptic membrane is on the neurone where the signal is going to.
• Between these two membranes is the synaptic cleft
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Synapse Depolarisation
• On the pre synaptic membrane are Calcium pumps which pump calcium out of the cell
• When the action potential arrives at the synapse is causes a voltage gates calcium channel to open
• This causes calcium to flood into the cell
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Neurotransmitter Secretion
• As the intracellular levels of calcium rise this triggers special synaptic vesicles containing neurotransmitters to fuse with the pre-synaptic membrane
• This causes neurotransmitters to be released (by exocytosis) into the synaptic cleft
• This exocytosis process uses ATP derived from mitochondria
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Synapse Mechanism
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Neurotransmitter Receptors
• Receptors on the post-synaptic membrane detect the neurotransmitters
• Sodium channels are then opened which cause a sodium to enter the cell creating a threshold potential
• This then sets off an action potential along the next membrane
• To stop the neurotransmitters effects, enzymes (e.g. acetylcholinase) break them down. This also stop neurone cross firing