Neurotransmitter

A neurotransmitter is a molecule used for signalling between nerve cells or neurons. Neurotransmitter molecules pass between neurons at synapses. Within the cell they are packaged in vesicles and released by rapid exocytosis upon the arrival of a nerve impulse, after which they diffuse across the synaptic gap to bind neurotransmitter receptors[?] or other ligand gated ion channels. The synaptic gap is permeated with neurotransmitter-degenerating enzymes, so that a neurotransmitter does not continue to stimulate or inhibit the firing of the postsynaptic neuron[?] for a long time.

Neurotransmitters may be either excitatory or inhibitory; that is, they may be of a type that fosters the initiation of a nerve impulse in the receiving neuron, or they may inhibit such an impulse (more at synapse). Most are small molecules derived from or related to amino acids. GABA and glycine are well-known inhibitory neurotransmitters.

There are many neurotransmitters; some of the important ones are:

• Amino acids:
  • aspartate[?]
  • glutamate
  • GABA
  • glycine

• Monoamines (in the order of their synthesis):
  • from phenylalanine:
    • dopamine
    • epinephrine
    • norepinephrine
  • from tryptophan:
    • serotonin
  • from histidine:
    • histamine[?]

• Other:
  • acetylcholine
  • nitric oxide