Neurotransmitters play an important role in transmitting information between neurons across the synaptic cleft. Various regions and pathways in the brain use different patterns of neurotransmitters and different receptor subclasses, which helps to identify the role specific neurotransmitters play in various psychiatric conditions in neuroimaging studies and can also make medication more specific.
Neurotransmitters are stored in synaptic vesicles in the axon terminal. Following a chemical or electric signal, the vesicles fuse with the membrane and release the neurotransmitter into the synaptic cleft. At the other end of the synapse, they bind to receptors on the membrane. The usual information transmission path is thus that a wave of electrical depolarisation migrates down the nerve fibre of one neuron, triggers a release of the neurotransmitter into the synapse, which is then picked up by the receptors on the nerve fibre of the next cell, where it leads to an electrical depolarisation or chemical signal. Information can be passed by this mechanism from one cell to the next along the nerve fibres of the cells contained in the neural network, while the neurotransmitter system allows to finetune and control it.
Presynaptic receptors may help in the autoregulation of the quantity of neurotransmitters released from an axon terminal into the synapse. They can, for example, inhibit the availability and release of neurotransmitters, when the neurotransmitter concentration outside the neuron is too high.
