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The Role Of Neurotransmitters In The Body
What Are Neurotransmitters? by Jane Thurnell-Read
Neurotransmitters are small molecules that transmit information across the junction that separates one nerve cell (neuron) from:
Neurotransmitters include serotonin, acetylcholine, dopamine and GABA. Some neurotransmitters (e.g. noradrenaline) also function as hormones. Most neurons use only one compound as their neurotransmitter.
Neurotransmitters are manufactured from compounds such as amino acids, glucose and choline, e.g. serotonin is derived from the amino acid tryptophan, GABA is made from glucose, and acetylcholine has choline as its precursor (raw material).
The site where neurons meet is called the synapse and consists of:
Molecules of neurotransmitters are stored in small "packages" called vesicles. When an electrical impulse travelling along a nerve reaches the axon, the vesicle fuses with the membrane of the axon terminal, spilling the neurotransmitter into the synaptic cleft. The neurotransmitter travels across the synapse. When enough of the neurotransmitter has made this journey, it either prompts or inhibits the electrical impulses along the new nerve. This allows impulses to be passed from one cell to the next throughout the nervous system.
Some neurotransmitters can be both excitatory and inhibitory, e.g. acetylcholine is excitatory at nerve/muscle junctions, but can be excitatory or inhibitory at nerve/nerve junctions.
A similar process happens if the post-synaptic cell is a muscle cell or a glandular cell rather than a neuron. An excitatory neurotransmitter will cause the muscle to contract or the cell to secrete its contents. An inhibitory neurotransmitter will damp down the activity of the muscle or secreting cell.
Once they have had the desired effect the neurotransmitters are cleared by: