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The key points covered of this video include:
1. Introduction to Synapse
2. The Presynaptic Bulb
3. The Synaptic Cleft
4. The Postsynaptic Neurone
Introduction to Synapses
A synapse links two or more neurones together. It allows the action potentials from one neurone to be communicated to the next. Information travels from the pre-synaptic neurone, across the synaptic cleft, to the post-synaptic neurone.
The Presynaptic Bulb
The pre-synaptic bulb (or knob) is a swelling at the end of the axon of the pre-synaptic neurone. It is filled with synaptic vesicles - these are vesicles filled with neurotransmitters. Neurotransmitters - like acetylcholine - are chemicals that stimulate the post-synaptic neurone. These vesicles are made in the smooth endoplasmic reticulum. The release of these vesicles requires ATP, so there are mitochondria in the pre-synaptic bulb. The final feature of synaptic bulbs is the presence of voltage-gated calcium channels. These detect when an action potential arrives at the end of the axon.
The Synaptic Cleft
When neurotransmitters are released from the pre-synaptic bulb they go into the synaptic cleft. It is about 20-30 nm wide - about the width of a bacterial flagellum. Also contained in the synaptic cleft are enzymes that break down the neurotransmitter.
The Postsynaptic Neurone
Once the neurotransmitter diffuses across the synaptic cleft it reaches the membrane of the post-synaptic neurone. On the membrane of the post-synaptic neurone there are neurotransmitter receptors. These are specialised ion channels that close or open when a neurotransmitter binds to them. In the case of a cholinergic synapse, an acetylcholine receptor opens up when acetylcholine binds. This causes sodium to enter into the cell.
Summary
Nerve impulses are transmitted from the pre-synaptic bulb, across the synaptic cleft, to the post-synaptic neurone
The pre-synaptic bulb contains vesicles of neurotransmitter
These are released into the synaptic cleft
Neurotransmitter then binds to receptors on the post-synaptic neurone