The document discusses ionotropic receptors, which are binding sites that open when ions attach. Ionotropic receptors directly activate ion channels, allowing molecules to move in and out. Metabotropic receptors are part of binding sites for neurotransmitters and indirectly regulate ion channels through complex processes. The autonomic nervous system controls smooth muscle, cardiac muscle, and organs through the sympathetic and parasympathetic branches, which use ionotropic and metabotropic receptors to regulate functions throughout the body.