This is an extract of our Neurotransmitters And Synapses document, which we sell as part of our BIOL10832 Excitable Cells Notes collection written by the top tier of University Of Manchester students.
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e-learning V - Neurotransmitters and Synapses
Serotonin, or 5-hydroxytryptamine (5HT) is an important neurotransmitter and neuromodulator. Defects in serotonin transmission are thought to be one of the causes of depression and many antidepressant therapies are aimed at boosting synaptic levels of serotonin. The brain has a vast array of serotonin receptors and they are a real pain to remember.
Chemical Transmission Revisited
In lectures to date you've been given an overview of "classic" transmission at chemical synapses.
The picture you've seen looks something like this:
In this model, an action potential reaching the presynaptic terminal causes the vesicles filled with neurotransmitter to fuse with the membrane. The neurotransmitter is released into the synapse and diffuses across to bind with receptors on the post-synaptic neurone.
Activation of these receptors causes signalling to continue in the postsynaptic neurone.
As you might already have guessed, things in the real world are a little more complicated! One of the added complications is that the nervous system has a variety of mechanisms for controlling the release of neurotransmitter from the pre-synaptic nerve terminal.
Our first example of the regulation of neurotransmitter release is a type of presynaptic receptor known as an autoreceptor.
Autoreceptors are receptors for the neurotransmitter released by the nerve terminal in whose membrane they reside and when activated, these receptors regulate the release of that neurotransmitter. Usually, this regulation takes the form of inhibition (ie: negative feedback), but there are some instances where positive feedback is seen. Though the presynaptic autoreceptor binds the same neurotransmitter as the postsynaptic receptor, it is often a different member of the same receptor family.
The figure sets out the general mechanism by which autoreceptors work:
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