View larger image | A nerve signal is passed from one cell to another at the synapse. As the signal approaches, ion channels open. An influx of ions triggers the release of a neurotransmitter, in this case glutamate. The glutamate stimulates receptors on the next nerve cell, causing ions to flow in and pass on the signal. One genetic variant linked to migraine may reduce the clearing of glutamate in the synapse by glial cells. Credit: T. Dubé