Glutamate: is also referred to as Glutamic Acid and is an essential amino acid. It is also the fastest neurotransmitter in the nervous system. It is stored in vesicles (like sacs) and then released once is reaches the end of the presynaptic neuron. It then crosses the space between the neurons and goes to the postsynaptic neuron.

Cited: Wikipedia.org. Updated 2006. Accessed 3 Dec 2006. http://en.wikipedia.org/wiki/Glutamate#As_a_neurotransmitter