The N-methyl-D-aspartate receptor (NMDA receptor) is a type of glutamate receptor in the brain that plays a crucial role in synaptic plasticity, which is essential for learning and memory. It is a ligand-gated ion channel that allows the flow of calcium, sodium, and potassium ions when activated by its specific neurotransmitter, glutamate, and a co-agonist, typically glycine or D-serine. NMDA receptors are unique because they require both ligand binding and a change in membrane potential to open. This dual requirement makes them important for detecting coincident signals in neuronal activity. Dysfunction of NMDA receptors is associated with various neurological disorders, including Alzheimer's disease and schizophrenia.