A cousin of the GABAA receptor, nAChRs are also made of five subunits that surround a central pore. This receptor permits the flow of sodium, rather than chloride, and because sodium ions carry a positive charge, nAChRs are excitatory. Nicotine activates these receptors by substituting for acetylcholine and thereby increasing neuronal activity. Also reminiscent of the GABAA receptor, much of the structural and functional diversity of nAChRs arises from the many possible subunit combinations; in this case, there are sixteen different subunits. These combine to form different nAChR subtypes,
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