To date, scientists have identified more than 60 distinct types of neurotransmitters in the human brain, and most experts say there are more left to discover. The neuropeptides, small molecules like insulin and oxytocin, work more subtly, modulating, or adjusting, how cells communicate at the synapse. Small-molecule transmitters, like dopamine and glutamate, typically act directly on neighboring cells. Neurotransmitters, at the highest level, can be sorted into two types: small-molecule transmitters and neuropeptides. Scientists call this phenomenon “neurotransmitter switching.” Types of Neurotransmitters Some cells change the type of neurotransmitters they release depending on the circumstances, sometimes releasing up to five different kinds. But new work in the field has uncovered that neurons are not fixed when it comes to the chemicals they release. Today, the majority of neuroscientists will tell you that most neurons release the same neurotransmitter from their axons-which is why you may see some neurons referred to as “dopaminergic” or “serotonergic,” releasing dopamine or serotonin, respectively. Eccles later revised Dale’s Law to say that specific neurons release a similar set of neurotransmitter types at their synapses, if not a single neurotransmitter. But as technologies and techniques in the field advanced, scientists saw that neurons can synthesize and release more than one type of neurotransmitter. This theory, called Dale’s Law, was suggested by Australian neurophysiologist and Nobel Laureate John Eccles based on the previous work of neuroscientist Henry Hallett Dale. When scientists first studied these powerful little neurochemicals, they believed each type of neuron released a single, unique neurotransmitter over its lifetime. Specific receptors on neighboring cells can then take up the neurotransmitters, which can increase or decrease the signal being passed along a particular circuit. When a cell is activated, these neurochemicals are released into the synapse from specialized pouches clustered near the cell membrane called synaptic vesicles. Neurotransmitters are endogenous-produced inside the neuron itself.
There are many types of neurotransmitters in the brain, but they do have a few things in common. Those chemical messages are unique molecules called neurotransmitters.
Those billions of brain cells communicate by passing chemical messages at the synapse, the small gap between cells, in a process called neurotransmission.
The human brain contains an estimated 86 billion neurons.
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