Polarized light micrograph of glycine crystals. This is the smallest amino acid, which is not essential in the human diet. Glycine is a major postsynaptic inhibitory neurotransmitter, acting in the spinal cord, brain stem, and retina. Glycine is used as a food additive (flavoring agent and antioxidant), in the elaboration of pet food and animal feed, and in pesticides like pyrethroid insecticides, the fungicide iprodione, and the herbicide glyphosate. Glycine may have antispastic, antipsychotic, anti-inflammatory, and antacid activities. It is therefore used to treat myasthenia gravis, progressive muscular atrophy, and hyperacidity. In space, glycine has been identified in comet Wild 2 (by the Stardust spacecraft), in the Murchison meteorite, and in comet 67P/Churyumov-Gerasimenko (by the Rosetta spacecraft). Field of view size: 0.30 x 0.45 mm (0.012 x 0.018 in)