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Neurotransmitter
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<p>A neurotransmitter is a <a href="/facts/Signaling_molecule/6oYAVP9I">signaling molecule</a> secreted by a <a href="/facts/Neuron/G7CyTVdH">neuron</a> to affect another cell across a <a href="/facts/Chemical_synapse/M1x5rhz7">synapse</a>. The cell receiving the signal, or target cell, may be another neuron, but could also be a <a href="/facts/Gland/gfq2of7k">gland</a> or <a href="/facts/Muscle_cell/cP7Jea3q">muscle cell</a>. </p><p>Neurotransmitters are released from <a href="/facts/Synaptic_vesicles/zE6oSYCG">synaptic vesicles</a> into the <a href="/facts/Synaptic_cleft/M1x5rhz7">synaptic cleft</a> where they are able to interact with <a href="/facts/Neurotransmitter_receptor/6a6WnCwT">neurotransmitter receptors</a> on the target cell. Some neurotransmitters are also stored in <a href="/facts/Large_dense_core_vesicles/m4TrnRNw">large dense core vesicles</a>. The neurotransmitter's effect on the target cell is determined by the receptor it binds to. Many neurotransmitters are synthesized from simple and plentiful precursors such as <a href="/facts/Amino_acid/WDxYwBny">amino acids</a>, which are readily available and often require a small number of <a href="/facts/Biosynthetic/aFk7Tk7f">biosynthetic</a> steps for conversion. </p><p>Neurotransmitters are essential to the function of complex neural systems. The exact number of unique neurotransmitters in humans is unknown, but more than 100 have been identified. Common neurotransmitters include <a href="/facts/Glutamate_(neurotransmitter)/GRqBSJ1P">glutamate</a>, <a href="/facts/GABA/vRTeQQUG">GABA</a>, <a href="/facts/Acetylcholine/v1d3wRUd">acetylcholine</a>, <a href="/facts/Glycine/3nXI1hqW">glycine</a>, <a href="/facts/Dopamine/5gNy8Xkd">dopamine</a> and <a href="/facts/Norepinephrine/AjTIC9ox">norepinephrine</a>. </p>