M1, Communication and homoeostasis: Nerve junctions.

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Nerve Junctions

Key terms for this topic:

Neurotransmitter: (transmitter substance) chemical that diffuses across the cleft of the synapse to transmit a signal to the postsynaptic neurone.

Cholinergic synapses: those that use acetylcholine as their transmitter substance

Synaptic knob: swelling at the end of the presynaptic neurone.

Acetylcholinesterase: enzyme in synaptic cleft. breaks down the transmitter substance acetylcholine.

Structure of a cholinergic synapse:

A synapse is a junction between one or more neurones, it is where one neurone can communicate with, or signal to, another neurone.

  • the synaptic cleft (small gap between two neurones) is 20nm wide
  • the action potential produced by movements of ions accross neurone membrane
  • note, the action potential cannot bridge the gap between two neurones, the presynaptic action potential causes release of the transmitter substance that diffuses across the gap and generates a new action potential in postsynaptic neurone.
  • synapses that use acetylcholine as the neurotransmitter are called cholinergic synapses.

The synaptic Knob contains a number of specialised features:


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