Humans (Homo sapiens) are the most abundant and widespread species of primates, characterized by bipedality and large, complex brains enabling the development of advanced tools, culture and language.

Numerous small molecules synthesized in the cytosol of axon terminals function as neurotransmitters at various chemical synapses. The “classic” neurotransmitters are stored in synaptic vesicles, uniformly sized organelles, 40 – 50 nm in diameter.