title: Cellular pacemakers: introduction.
mesh_terms: D000200:Action Potentials; D000818:Animals; D006321:Heart / Q000502:physiology*; D006801:Humans; D009130:Muscle, Smooth / Q000502:physiology*; D009474:Neurons / Q000502:physiology* / Q000648:ultrastructure; D010507:Periodicity; D013569:Synapses / Q000502:physiology