Template:Synapse map Neurotransmitters are endogenous chemicals
which transmit signals from a neuron to a target cell across a
synapse. Neurotransmitters are packaged into synaptic vesicles
clustered beneath the membrane on the presynaptic side of a
synapse, and are released into the synaptic cleft, where they
bind to receptors in the membrane on the postsynaptic side of
the synapse. Release of neurotransmitters usually follows
arrival of an action potential at the synapse, but may also
follow graded electrical potentials. Low level "baseline"
release also occurs without electrical stimulation.
Neurotransmitters are synthesized from plentiful and simple
precursors, such as amino acids, which are readily available
from the diet and which require only a small number of
biosynthetic steps to convert. Until the early 20th century,
scientists assumed that synaptic communication was electrical.
However, through the careful histological examinations of Ramón
y Cajal (1852–1934), a 20 to 40 nm gap between neurons, kn