a chemical substance that transmits information from one neuron to another neuron at a very short distance. Neurotransmitters are released by nerve cells into the extra cellular space at synapses. The release of neurotransmitter then produces either excitation or inhibition of an immediately neighbouring nerve cell. Many substances act both as hormone in the blood and neurotransmitters in either the central or peripheral nervous systems. Neurotransmitters in the brain can be generally divided into two large classes. Classical neurotransmitters, such as norepinephrine, are synthesized in nerve terminals close to the synapse, whereas the neuropeptide neurotransmitters, such as the endorphins, are synthesized in body of the nerve cell.