▁are ▁two ▁main ▁kinds ▁of ▁" ch ol iner g ic " ▁re cept ors . ▁ ▁Re ceptor ▁types ▁M ole cular ▁bi ology ▁has ▁shown ▁that ▁the ▁nic ot in ic ▁and ▁mus car in ic ▁re cept ors ▁belong ▁to ▁distinct ▁protein ▁super famil ies . ▁Nic ot in ic ▁re cept ors ▁are ▁of ▁two ▁types : ▁N m ▁and ▁N n . ▁N m ▁is ▁located ▁in ▁the ▁neur om us cular ▁j unction ▁which ▁causes ▁the ▁contra ction ▁of ▁ske let al ▁mus cles ▁by ▁way ▁of ▁end - plate ▁potential ▁( EP P s ). ▁N n ▁causes ▁dep olar ization ▁in ▁autonom ic ▁gang lia ▁resulting ▁in ▁post ▁gang l ionic ▁imp ulse . ▁Nic ot in ic ▁re cept ors ▁cause ▁the ▁release ▁of ▁c ate ch ol am ine ▁from ▁the ▁ad ren al ▁med ulla , ▁and ▁also ▁site ▁specific ▁exc itation ▁or ▁in hib ition ▁in ▁brain . ▁Both ▁N m ▁and ▁N n ▁are ▁Na + ▁and ▁Ca 2 + ▁channel ▁linked ▁but ▁N n ▁is ▁also ▁linked ▁with ▁an ▁extra ▁K + ▁channel . ▁ ▁n A Ch R ▁ ▁The ▁n A Ch R s ▁are ▁lig and - g ated ▁ion ▁channels , ▁and , ▁like ▁other ▁members ▁of ▁the ▁" c ys - loop " ▁lig and - g ated ▁ion ▁channel ▁super family , ▁are ▁composed ▁of ▁five ▁protein ▁sub un its ▁symmet r ically ▁arranged ▁like ▁st aves ▁around ▁a ▁bar rel . ▁The