, ▁many ▁of ▁these ▁processes ▁including ▁mus cle ▁relax ation , ▁hy pert ension , ▁ins ul in ▁secret ion ▁etc . ▁Some ▁examples ▁of ▁pot ass ium ▁ion ▁channels ▁within ▁bi ological ▁systems ▁include ▁K AT P ▁channels , ▁Big ▁pot ass ium ▁channels , ▁and ▁E ther - à - go - go ▁pot ass ium ▁channels ▁ ▁Na + ▁Ch annels ▁ ▁S od ium ▁ion ▁channels ▁provide ▁an ▁integral ▁service ▁through ▁the ▁body , ▁as ▁they ▁transmit ▁dep olar izing ▁imp uls es ▁at ▁the ▁cell ular ▁and ▁int rac ell ular ▁level . ▁This ▁allows ▁sod ium ▁ ions ▁to ▁coordinate ▁much ▁more ▁int ensive ▁processes ▁such ▁as ▁movement ▁and ▁cogn ition . ▁S od ium ▁ion ▁channels ▁consist ▁of ▁various ▁sub un its , ▁however , ▁only ▁the ▁principle ▁sub unit ▁is ▁required ▁for ▁function . ▁These ▁sod ium ▁ion ▁channels ▁consist ▁of ▁four ▁internally ▁hom olog ous ▁domains , ▁each ▁of ▁which ▁containing ▁six ▁transm emb rane ▁segments ▁and ▁res emb ling ▁a ▁single ▁sub unit ▁of ▁a ▁voltage - dependent ▁pot ass ium ▁ion ▁channel . ▁The ▁four ▁domains ▁fol d ▁together , ▁forming ▁a ▁central ▁p ore . ▁That ▁central ▁p ore ▁of ▁the ▁sod ium ▁ ions ▁dict ates ▁the ▁select ivity ▁of ▁the ▁channel : ▁both ▁ion ic ▁radius ▁and ▁ion ic ▁charge ▁are ▁key ▁in ▁channel ▁select ivity . ▁ ▁Cl - ▁Ch annels ▁ ▁Ch lor ide ▁ion ▁channels ▁vary ▁from ▁many ▁other ▁ion ▁channels ▁due ▁to ▁being ▁controlled ▁by