magnesium ion (Mg2+)

A magnesium atom that has lost two electrons. In the nervous system, a single magnesium ion blocks the opening of each of the cell’s NMDA receptor, preventing the influx of calcium ions into the cell. This magnesium ion is removed only when the electrical charge inside the cell rises above a certain value. This increase in charge is mediated by the binding of glutamate to non-NMDA receptors.