Receptor operated channels (ROCs) such as the nicotinic acetylcholine, glutamate ionotropic NMDA and AMPA or the ionotropic purinergic (P2X) receptors are ligand-activated ion channels which in the open state allow for the flow of ions, including Ca2+ to which they are permeable. In addition the group I metabotropic glutamate receptors, which are G protein-coupled (GPCR), stimulate phospholipase activity to generate IP3 and DAG second messengers. IP3 leads to calcium entry into the cell by activating IP3 receptors in the ER.
These channels are not presented here but will be within the context of neurotransmitters/small molecule signaling pathways with which they are associated.
For more details on ROCs involvement in Ca2+ transport and signaling, check PMIDs 22435804, 18083096 and references therein.