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[[File:Synapse.png|thumb|250px|A synapse junction (terms are in French)]]

'''Neurotransmitters''' are [[chemical]] messengers. They send [[information]] between [[neuron]]s by crossing a [[synapse]]. Electrical signals are not able to cross the gap between most neurons. They are changed into chemical signals to cross the gap. Neurotransmitters act mostly on [[chemical synapse]]s. Once they reach the next neuron they are absorbed. The neuron then changes this chemical signal back into an electrical signal called an [[action potential]]. The action potential passes across the next neuron and to the next synapse.

Many neurotransmitters are made from [[amino acid]]s, which are part of your diet and it takes only a few steps to convert them. Neurotransmitters play a major role in shaping everyday life and functions. Scientists do not yet know exactly how many neurotransmitters exist, but more than 100&nbsp;chemical messengers have been identified.<ref>{{cite web|last1=Cherry|first1=Kendra|title=What is a neurotransmitter?|url=http://psychology.about.com/od/nindex/g/neurotransmitter.htm|accessdate=6 October 2014|archive-date=4 March 2016|archive-url=https://web.archive.org/web/20160304200131/http://psychology.about.com/od/nindex/g/neurotransmitter.htm|url-status=dead}}</ref>

Each neurotransmitter has a different function. For example: [[dopamine]] is used in reward and pleasure and [[noradrenaline]] is used in an animal's "[[Fight or flight response|fight or flight]]" response. Neurotransmitters also regulate the passing of messages. This is because an action potential must be a certain strength before the neurotransmitters are released. The strength required to release the neurotransmitter is called a threshold.

The most common transmitter is [[glutamate]], which is excitatory at well over 90% of the synapses in the human [[brain]].<ref>Robert Sapolsky 2005. ''Biology and human behavior: the neurological origins of individuality''. 2nd ed, The Teaching Company, pages 13 & 14 of guide book.</ref> The next most prevalent is called [[GABA]], which inhibits at more than 90% of the synapses that do not use glutamate.

Neurotransmitters are transported within neurons by small "sacks" called [[vesicles]]. When these vesciles come into contact with the neuron's [[cell membrane]], it opens. This releases the neurotransmitters into the [[synaptic cleft]].

==Discovery==
Until the early 20th century, scientists assumed that the majority of synaptic communication in the brain was electrical. However, through the careful [[Histology|histological]] examinations by [[Ramón y Cajal]] (1852–1934), a 20 to 40&nbsp;nm gap between neurons, known today as the [[synaptic cleft]], was discovered. The presence of the gap suggested chemical messengers moved across the synaptic cleft. In 1921 German pharmacologist [[Otto Loewi]] (1873–1961) confirmed that neurons can communicate by releasing chemicals. By experiments involving the [[vagus nerve]]s of frogs, Loewi was able to slow the [[heart rate]] of frogs by controlling the amount of [[saline]] solution present around the vagus nerve.

Loewi asserted that [[sympathetic nervous system|sympathetic]] regulation of cardiac function can be mediated through changes in chemical concentrations. Otto Loewi also discovered [[acetylcholine]] (ACh)—the first known neurotransmitter.<ref>Saladin, Kenneth S. 2009. ''Anatomy and physiology: the unity of form and function''. McGraw Hill. {{ISBN|0-07-727620-5}}</ref> Some neurons do, however, communicate by [[electrical synapse]]s through the use of [[gap junction]]s, which allow specific [[ions]] to pass directly from one cell to another.<ref name="gap">{{cite web |url=http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/J/Junctions.html |title=Junctions Between Cells |accessdate=22 November 2010 |archive-date=8 August 2011 |archive-url=https://web.archive.org/web/20110808065154/http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/J/Junctions.html |url-status=dead }}</ref>

== References ==
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[[Category:Neuroscience]]