Illustration of the central nervous system, from the brain to the synapse. Top right is the brain seen in profile, then a close-up of the neuronal system. A neuron and its axon are visible around which oligodendrocytes (small pinky purple cells) form an insulating sheath allowing a faster electrical signal from one neuron to another. Finally, an illustration of the transmission of a nervous impulse between two neurons.Vesicles release glutamate (orange balls) that fix onto receptors (purple) that open sodium channels allowing Na+ ions to penetrate the B neuron's terminal dendrite buttons, creating an electrical current.