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| chenhongxia Quote | Reply | | Neurotransmitters posted on: 8/6/2008 11:37:46 PM Neurotransmitters are chemical messengers produced by the nervous systems of higher organisms in order to relay a nerve impulse from one cell to another cell. The two cells may be nerve cells, also called neurons, or one of the cells may be a different type, such as a muscle or gland cell. A chemical messenger is necessary for rapid communication between cells if there are small gaps of 20 to 50 nanometers (7.874 ¡Á 10−7¨C19.69 ¡Á10−7 inches), called synapses or synaptic clefts, between the two cells. The two cells are referred to as either presynaptic or postsynaptic. The term "presynaptic" refers to the neuron that produces and releases the neurotransmitter, whereas "postsynaptic" refers to the cell that receives this chemical message.Neurotransmitters include small molecules with amine functional groups such as acetylcholine , certain amino acids, amino acid derivatives, and peptides. Through a series of chemical reactions, the amino acid tyrosineis converted into the catecholamine neurotransmitters dopamine and norepinephrine or into the hormone epinephrine. Other neurotransmitters that are amino acid derivatives include ¦Ã-aminobutyric acid, made from glutamate, and serotonin, made from the amino acid tryptophan.Peptide neurotransmitters include the enkephalins, the endorphins, oxytocin, substance P, vasoactive intestinal peptide, and many others. The gaseous free radical nitric oxide is one of the more recent molecules to be added to the list of possible neurotransmitters. It is commonly believed that there may be fifty or more neurotransmitters. Although there are many different neurotransmitters, there is a common theme by which they are released and exert their actions. In addition, there is always a mechanism for termination of the chemical message.(from chemistryexplain) |
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