Illustration showing the mechanism behind long term potentiation (LTP), the persistent strengthening of a synapse. An influx of calcium ions (red) through an NMDA (N-methyl-D-aspartate) receptor (left) leads to the ions binding to a calmodulin (CaM) molecule, which in turn binds to a calcium/calmodulin-dependent protein kinase II (CaMKII) molecule, activating it. The activated CaMKII molecule phosphorylates AMPA (a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors (right), increasing their activity and therefore strengthening the synapse. LTP plays an important role in learning and memory.