Astrocyte/neuron synapse in the brain. Artwork of a nerve cell (neuron, yellow) synapse in the brain with an associated regulatory astrocyte cell (red). The neuron passes its signal (arrows) from the top cell to the bottom one by releasing the neurotransmitter chemical glutamate (green balls). This binds to receptors on the target cell, creating a new nerve signal. The process is regulated by the actions of the astrocyte cell. This can take up excess glutamate (as at right), sequester it using a protein (purple rings, left), or produce a chemical (white balls) that reduces its production (upper right). It can also increase the signal by releasing its own glutamate, as at upper left.