The muscarinic antagonists compete with neurally released  acetylcholine ( ACh )   for access to muscarinic cholinoceptors and block  ACh’s  effects. The results are faster heart rate, sedation,  and dry mouth. With the exception of the quaternary  ammonium compounds that do not readily cross the  blood-brain barrier and have few actions on the CNS,  there is no significant specificity of action among these  drugs; they block all muscarinic effects with equal efficacy,  although there are some quantitative differences in  effect.